I'm in the process of reading the code, and got some questions/comments.
-Chema
On Fri, Jun 27, 2014 at 5:06 PM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote:
> Safety of eBPF programs is statically determined by the verifier, which detects:
> - loops
> - out of range jumps
> - unreachable instructions
> - invalid instructions
> - uninitialized register access
> - uninitialized stack access
> - misaligned stack access
> - out of range stack access
> - invalid calling convention
>
> It checks that
> - R1-R5 registers statisfy function prototype
> - program terminates
> - BPF_LD_ABS|IND instructions are only used in socket filters
>
> It is configured with:
>
> - bool (*is_valid_access)(int off, int size, enum bpf_access_type type);
> that provides information to the verifer which fields of 'ctx'
> are accessible (remember 'ctx' is the first argument to eBPF program)
>
> - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id);
> reports argument types of kernel helper functions that eBPF program
> may call, so that verifier can checks that R1-R5 types match prototype
>
> More details in Documentation/networking/filter.txt
>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
> ---
> Documentation/networking/filter.txt | 233 ++++++
> include/linux/bpf.h | 48 ++
> include/uapi/linux/bpf.h | 1 +
> kernel/bpf/Makefile | 2 +-
> kernel/bpf/syscall.c | 2 +-
> kernel/bpf/verifier.c | 1431 +++++++++++++++++++++++++++++++++++
> 6 files changed, 1715 insertions(+), 2 deletions(-)
> create mode 100644 kernel/bpf/verifier.c
>
> diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
> index e14e486f69cd..05fee8fcedf1 100644
> --- a/Documentation/networking/filter.txt
> +++ b/Documentation/networking/filter.txt
> @@ -995,6 +995,108 @@ BPF_XADD | BPF_DW | BPF_STX: lock xadd *(u64 *)(dst_reg + off16) += src_reg
> Where size is one of: BPF_B or BPF_H or BPF_W or BPF_DW. Note that 1 and
> 2 byte atomic increments are not supported.
>
> +eBPF verifier
> +-------------
> +The safety of the eBPF program is determined in two steps.
> +
> +First step does DAG check to disallow loops and other CFG validation.
> +In particular it will detect programs that have unreachable instructions.
> +(though classic BPF checker allows them)
> +
> +Second step starts from the first insn and descends all possible paths.
> +It simulates execution of every insn and observes the state change of
> +registers and stack.
> +
> +At the start of the program the register R1 contains a pointer to context
> +and has type PTR_TO_CTX.
> +If verifier sees an insn that does R2=R1, then R2 has now type
> +PTR_TO_CTX as well and can be used on the right hand side of expression.
> +If R1=PTR_TO_CTX and insn is R2=R1+R1, then R2=INVALID_PTR,
> +since addition of two valid pointers makes invalid pointer.
> +
> +If register was never written to, it's not readable:
> + bpf_mov R0 = R2
> + bpf_exit
> +will be rejected, since R2 is unreadable at the start of the program.
> +
> +After kernel function call, R1-R5 are reset to unreadable and
> +R0 has a return type of the function.
> +
> +Since R6-R9 are callee saved, their state is preserved across the call.
> + bpf_mov R6 = 1
> + bpf_call foo
> + bpf_mov R0 = R6
> + bpf_exit
> +is a correct program. If there was R1 instead of R6, it would have
> +been rejected.
> +
> +Classic BPF register X is mapped to eBPF register R7 inside sk_convert_filter(),
> +so that its state is preserved across calls.
> +
> +load/store instructions are allowed only with registers of valid types, which
> +are PTR_TO_CTX, PTR_TO_MAP, PTR_TO_STACK. They are bounds and alignment checked.
> +For example:
> + bpf_mov R1 = 1
> + bpf_mov R2 = 2
> + bpf_xadd *(u32 *)(R1 + 3) += R2
> + bpf_exit
> +will be rejected, since R1 doesn't have a valid pointer type at the time of
> +execution of instruction bpf_xadd.
> +
> +At the start R1 contains pointer to ctx and R1 type is PTR_TO_CTX.
> +ctx is generic. verifier is configured to known what context is for particular
> +class of bpf programs. For example, context == skb (for socket filters) and
> +ctx == seccomp_data for seccomp filters.
> +A callback is used to customize verifier to restrict eBPF program access to only
> +certain fields within ctx structure with specified size and alignment.
> +
> +For example, the following insn:
> + bpf_ld R0 = *(u32 *)(R6 + 8)
> +intends to load a word from address R6 + 8 and store it into R0
> +If R6=PTR_TO_CTX, via is_valid_access() callback the verifier will know
> +that offset 8 of size 4 bytes can be accessed for reading, otherwise
> +the verifier will reject the program.
> +If R6=PTR_TO_STACK, then access should be aligned and be within
> +stack bounds, which are [-MAX_BPF_STACK, 0). In this example offset is 8,
> +so it will fail verification, since it's out of bounds.
> +
> +The verifier will allow eBPF program to read data from stack only after
> +it wrote into it.
> +Classic BPF verifier does similar check with M[0-15] memory slots.
> +For example:
> + bpf_ld R0 = *(u32 *)(R10 - 4)
> + bpf_exit
> +is invalid program.
> +Though R10 is correct read-only register and has type PTR_TO_STACK
> +and R10 - 4 is within stack bounds, there were no stores into that location.
> +
> +Pointer register spill/fill is tracked as well, since four (R6-R9)
> +callee saved registers may not be enough for some programs.
> +
> +Allowed function calls are customized with bpf_verifier_ops->get_func_proto()
> +For example, skb_get_nlattr() function has the following definition:
> + struct bpf_func_proto proto = {RET_INTEGER, PTR_TO_CTX};
> +and eBPF verifier will check that this function is always called with first
> +argument being 'ctx'. In other words R1 must have type PTR_TO_CTX
> +at the time of bpf_call insn.
> +After the call register R0 will be set to readable state, so that
> +program can access it.
> +
> +Function calls is a main mechanism to extend functionality of eBPF programs.
> +Socket filters may let programs to call one set of functions, whereas tracing
> +filters may allow completely different set.
> +
> +If a function made accessible to eBPF program, it needs to be thought through
> +from security point of view. The verifier will guarantee that the function is
> +called with valid arguments.
> +
> +seccomp vs socket filters have different security restrictions for classic BPF.
> +Seccomp solves this by two stage verifier: classic BPF verifier is followed
> +by seccomp verifier. In case of eBPF one configurable verifier is shared for
> +all use cases.
> +
> +See details of eBPF verifier in kernel/bpf/verifier.c
> +
> eBPF maps
> ---------
> 'maps' is a generic storage of different types for sharing data between kernel
> @@ -1064,6 +1166,137 @@ size. It will not let programs pass junk values as 'key' and 'value' to
> bpf_map_*_elem() functions, so these functions (implemented in C inside kernel)
> can safely access the pointers in all cases.
>
> +Understanding eBPF verifier messages
> +------------------------------------
> +
> +The following are few examples of invalid eBPF programs and verifier error
> +messages as seen in the log:
> +
> +Program with unreachable instructions:
> +static struct sock_filter_int prog[] = {
> + BPF_EXIT_INSN(),
> + BPF_EXIT_INSN(),
> +};
> +Error:
> + unreachable insn 1
> +
> +Program that reads uninitialized register:
> + BPF_ALU64_REG(BPF_MOV, BPF_REG_0, BPF_REG_2),
> + BPF_EXIT_INSN(),
> +Error:
> + 0: (bf) r0 = r2
> + R2 !read_ok
> +
> +Program that doesn't initialize R0 before exiting:
> + BPF_ALU64_REG(BPF_MOV, BPF_REG_2, BPF_REG_1),
> + BPF_EXIT_INSN(),
> +Error:
> + 0: (bf) r2 = r1
> + 1: (95) exit
> + R0 !read_ok
> +
> +Program that accesses stack out of bounds:
> + BPF_ST_MEM(BPF_DW, BPF_REG_10, 8, 0),
> + BPF_EXIT_INSN(),
> +Error:
> + 0: (7a) *(u64 *)(r10 +8) = 0
> + invalid stack off=8 size=8
> +
> +Program that doesn't initialize stack before passing its address into function:
> + BPF_ALU64_REG(BPF_MOV, BPF_REG_2, BPF_REG_10),
> + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> + BPF_ALU64_IMM(BPF_MOV, BPF_REG_1, 1),
> + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
> + BPF_EXIT_INSN(),
> +Error:
> + 0: (bf) r2 = r10
> + 1: (07) r2 += -8
> + 2: (b7) r1 = 1
> + 3: (85) call 1
> + invalid indirect read from stack off -8+0 size 8
> +
> +Program that uses invalid map_id=2 while calling to map_lookup_elem() function:
> + BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
> + BPF_ALU64_REG(BPF_MOV, BPF_REG_2, BPF_REG_10),
> + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> + BPF_ALU64_IMM(BPF_MOV, BPF_REG_1, 2),
> + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
> + BPF_EXIT_INSN(),
> +Error:
> + 0: (7a) *(u64 *)(r10 -8) = 0
> + 1: (bf) r2 = r10
> + 2: (07) r2 += -8
> + 3: (b7) r1 = 2
> + 4: (85) call 1
> + invalid access to map_id=2
> +
> +Program that doesn't check return value of map_lookup_elem() before accessing
> +map element:
> + BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
> + BPF_ALU64_REG(BPF_MOV, BPF_REG_2, BPF_REG_10),
> + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> + BPF_ALU64_IMM(BPF_MOV, BPF_REG_1, 1),
> + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
> + BPF_ST_MEM(BPF_DW, BPF_REG_0, 0, 0),
> + BPF_EXIT_INSN(),
> +Error:
> + 0: (7a) *(u64 *)(r10 -8) = 0
> + 1: (bf) r2 = r10
> + 2: (07) r2 += -8
> + 3: (b7) r1 = 1
> + 4: (85) call 1
> + 5: (7a) *(u64 *)(r0 +0) = 0
> + R0 invalid mem access 'map_value_or_null'
> +
> +Program that correctly checks map_lookup_elem() returned value for NULL, but
> +accesses the memory with incorrect alignment:
> + BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
> + BPF_ALU64_REG(BPF_MOV, BPF_REG_2, BPF_REG_10),
> + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> + BPF_ALU64_IMM(BPF_MOV, BPF_REG_1, 1),
> + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
> + BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1),
> + BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0),
> + BPF_EXIT_INSN(),
> +Error:
> + 0: (7a) *(u64 *)(r10 -8) = 0
> + 1: (bf) r2 = r10
> + 2: (07) r2 += -8
> + 3: (b7) r1 = 1
> + 4: (85) call 1
> + 5: (15) if r0 == 0x0 goto pc+1
> + R0=map_value1 R10=fp
> + 6: (7a) *(u64 *)(r0 +4) = 0
> + misaligned access off 4 size 8
> +
> +Program that correctly checks map_lookup_elem() returned value for NULL and
> +accesses memory with correct alignment in one side of 'if' branch, but fails
> +to do so in the other side of 'if' branch:
> + BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
> + BPF_ALU64_REG(BPF_MOV, BPF_REG_2, BPF_REG_10),
> + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> + BPF_ALU64_IMM(BPF_MOV, BPF_REG_1, 1),
> + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
> + BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
> + BPF_ST_MEM(BPF_DW, BPF_REG_0, 0, 0),
> + BPF_EXIT_INSN(),
> + BPF_ST_MEM(BPF_DW, BPF_REG_0, 0, 1),
> + BPF_EXIT_INSN(),
> +Error:
> + 0: (7a) *(u64 *)(r10 -8) = 0
> + 1: (bf) r2 = r10
> + 2: (07) r2 += -8
> + 3: (b7) r1 = 1
> + 4: (85) call 1
> + 5: (15) if r0 == 0x0 goto pc+2
> + R0=map_value1 R10=fp
> + 6: (7a) *(u64 *)(r0 +0) = 0
> + 7: (95) exit
> +
> + from 5 to 8: R0=imm0 R10=fp
> + 8: (7a) *(u64 *)(r0 +0) = 1
> + R0 invalid mem access 'imm'
> +
> Testing
> -------
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 7bfcad87018e..67fd49eac904 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -47,17 +47,63 @@ struct bpf_map_type_list {
> void bpf_register_map_type(struct bpf_map_type_list *tl);
> struct bpf_map *bpf_map_get(u32 map_id);
>
> +/* types of values:
> + * - stored in an eBPF register
> + * - passed into helper functions as an argument
> + * - returned from helper functions
> + */
> +enum bpf_reg_type {
> + INVALID_PTR, /* reg doesn't contain a valid pointer */
> + PTR_TO_CTX, /* reg points to bpf_context */
> + PTR_TO_MAP, /* reg points to map element value */
> + PTR_TO_MAP_CONDITIONAL, /* points to map element value or NULL */
> + PTR_TO_STACK, /* reg == frame_pointer */
> + PTR_TO_STACK_IMM, /* reg == frame_pointer + imm */
> + PTR_TO_STACK_IMM_MAP_KEY, /* pointer to stack used as map key */
> + PTR_TO_STACK_IMM_MAP_VALUE, /* pointer to stack used as map elem */
> + RET_INTEGER, /* function returns integer */
> + RET_VOID, /* function returns void */
> + CONST_ARG, /* function expects integer constant argument */
> + CONST_ARG_MAP_ID, /* int const argument that is used as map_id */
> + /* int const argument indicating number of bytes accessed from stack
> + * previous function argument must be ptr_to_stack_imm
> + */
> + CONST_ARG_STACK_IMM_SIZE,
> +};
> +
> /* eBPF function prototype used by verifier to allow BPF_CALLs from eBPF programs
> * to in-kernel helper functions and for adjusting imm32 field in BPF_CALL
> * instructions after verifying
> */
> struct bpf_func_proto {
> s32 func_off;
> + enum bpf_reg_type ret_type;
> + enum bpf_reg_type arg1_type;
> + enum bpf_reg_type arg2_type;
> + enum bpf_reg_type arg3_type;
> + enum bpf_reg_type arg4_type;
> + enum bpf_reg_type arg5_type;
> +};
> +
> +/* bpf_context is intentionally undefined structure. Pointer to bpf_context is
> + * the first argument to eBPF programs.
> + * For socket filters: 'struct bpf_context *' == 'struct sk_buff *'
> + */
> +struct bpf_context;
> +
> +enum bpf_access_type {
> + BPF_READ = 1,
> + BPF_WRITE = 2
> };
>
> struct bpf_verifier_ops {
> /* return eBPF function prototype for verification */
> const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id);
> +
> + /* return true if 'size' wide access at offset 'off' within bpf_context
> + * with 'type' (read or write) is allowed
> + */
> + bool (*is_valid_access)(int off, int size, enum bpf_access_type type);
> };
>
> struct bpf_prog_type_list {
> @@ -78,5 +124,7 @@ struct bpf_prog_info {
>
> void free_bpf_prog_info(struct bpf_prog_info *info);
> struct sk_filter *bpf_prog_get(u32 prog_id);
> +/* verify correctness of eBPF program */
> +int bpf_check(struct sk_filter *fp);
>
> #endif /* _LINUX_BPF_H */
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index ed067e245099..597a35cc101d 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -381,6 +381,7 @@ enum bpf_prog_attributes {
>
> enum bpf_prog_type {
> BPF_PROG_TYPE_UNSPEC,
> + BPF_PROG_TYPE_SOCKET_FILTER,
> };
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> index 558e12712ebc..95a9035e0f29 100644
> --- a/kernel/bpf/Makefile
> +++ b/kernel/bpf/Makefile
> @@ -1 +1 @@
> -obj-y := core.o syscall.o hashtab.o
> +obj-y := core.o syscall.o hashtab.o verifier.o
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 836809b1bc4e..48d8f43da151 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -554,7 +554,7 @@ static int bpf_prog_load(int prog_id, enum bpf_prog_type type,
> mutex_lock(&bpf_map_lock);
>
> /* run eBPF verifier */
> - /* err = bpf_check(prog); */
> + err = bpf_check(prog);
>
> if (err == 0 && prog->info->used_maps) {
> /* program passed verifier and it's using some maps,
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> new file mode 100644
> index 000000000000..470fce48b3b0
> --- /dev/null
> +++ b/kernel/bpf/verifier.c
> @@ -0,0 +1,1431 @@
> +/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of version 2 of the GNU General Public
> + * License as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + * General Public License for more details.
> + */
> +#include <linux/kernel.h>
> +#include <linux/types.h>
> +#include <linux/slab.h>
> +#include <linux/bpf.h>
> +#include <linux/filter.h>
> +#include <linux/capability.h>
> +
> +/* bpf_check() is a static code analyzer that walks the BPF program
> + * instruction by instruction and updates register/stack state.
> + * All paths of conditional branches are analyzed until 'ret' insn.
> + *
> + * At the first pass depth-first-search verifies that the BPF program is a DAG.
> + * It rejects the following programs:
> + * - larger than BPF_MAXINSNS insns
> + * - if loop is present (detected via back-edge)
> + * - unreachable insns exist (shouldn't be a forest. program = one function)
This seems to me an unnecessary style restriction on user code.
> + * - ret insn is not a last insn
> + * - out of bounds or malformed jumps
> + * The second pass is all possible path descent from the 1st insn.
> + * Conditional branch target insns keep a link list of verifier states.
> + * If the state already visited, this path can be pruned.
> + * If it wasn't a DAG, such state prunning would be incorrect, since it would
> + * skip cycles. Since it's analyzing all pathes through the program,
> + * the length of the analysis is limited to 32k insn, which may be hit even
> + * if insn_cnt < 4K, but there are too many branches that change stack/regs.
> + * Number of 'branches to be analyzed' is limited to 1k
> + *
> + * All registers are 64-bit (even on 32-bit arch)
> + * R0 - return register
> + * R1-R5 argument passing registers
> + * R6-R9 callee saved registers
> + * R10 - frame pointer read-only
> + *
> + * At the start of BPF program the register R1 contains a pointer to bpf_context
> + * and has type PTR_TO_CTX.
> + *
> + * R10 has type PTR_TO_STACK. The sequence 'mov Rd, R10; add Rd, imm' changes
> + * Rd state to PTR_TO_STACK_IMM and immediate constant is saved for further
> + * stack bounds checking
> + *
> + * registers used to pass pointers to function calls are verified against
> + * function prototypes
> + *
> + * Example: before the call to bpf_map_lookup_elem(),
> + * R1 must contain integer constant and R2 PTR_TO_STACK_IMM_MAP_KEY
> + * Integer constant in R1 is a map_id. The verifier checks that map_id is valid
> + * and corresponding map->key_size fetched to check that
> + * [R3, R3 + map_info->key_size) are within stack limits and all that stack
> + * memory was initiliazed earlier by BPF program.
> + * After bpf_table_lookup() call insn, R0 is set to PTR_TO_MAP_CONDITIONAL
> + * R1-R5 are cleared and no longer readable (but still writeable).
> + *
> + * bpf_table_lookup() function returns ether pointer to map value or NULL
> + * which is type PTR_TO_MAP_CONDITIONAL. Once it passes through !=0 insn
> + * the register holding that pointer in the true branch changes state to
> + * PTR_TO_MAP and the same register changes state to INVALID_PTR in the false
> + * branch. See check_cond_jmp_op()
> + *
> + * load/store alignment is checked
> + * Ex: BPF_STX|BPF_W [Rd + 3] = Rs is rejected, because it's misaligned
> + *
> + * load/store to stack bounds checked and register spill is tracked
> + * Ex: BPF_STX|BPF_B [R10 + 0] = Rs is rejected, because it's out of bounds
> + *
> + * load/store to map bounds checked and map_id provides map size
> + * Ex: BPF_STX|BPF_H [Rd + 8] = Rs is ok, if Rd is PTR_TO_MAP and
> + * 8 + sizeof(u16) <= map_info->value_size
> + *
> + * load/store to bpf_context checked against known fields
> + */
> +#define _(OP) ({ int ret = OP; if (ret < 0) return ret; })
+1 to removing the _ macro. If you want to avoid the 3 lines (is there
anything in the style guide against "if ((err=OP) < 0) ..." ?), at
least use some meaningful macro name (DO_AND_CHECK, or something like
that).
> +
> +struct reg_state {
> + enum bpf_reg_type ptr;
> + int imm;
> + bool read_ok;
> +};
> +
> +enum bpf_stack_slot_type {
> + STACK_INVALID, /* nothing was stored in this stack slot */
> + STACK_SPILL, /* 1st byte of register spilled into stack */
> + STACK_SPILL_PART, /* other 7 bytes of register spill */
> + STACK_MISC /* BPF program wrote some data into this slot */
> +};
> +
> +struct bpf_stack_slot {
> + enum bpf_stack_slot_type type;
> + enum bpf_reg_type ptr;
> + int imm;
> +};
> +
> +/* state of the program:
> + * type of all registers and stack info
> + */
> +struct verifier_state {
> + struct reg_state regs[MAX_BPF_REG];
> + struct bpf_stack_slot stack[MAX_BPF_STACK];
> +};
> +
> +/* linked list of verifier states used to prune search */
> +struct verifier_state_list {
> + struct verifier_state state;
> + struct verifier_state_list *next;
> +};
> +
> +/* verifier_state + insn_idx are pushed to stack when branch is encountered */
> +struct verifier_stack_elem {
> + /* verifer state is 'st'
> + * before processing instruction 'insn_idx'
> + * and after processing instruction 'prev_insn_idx'
> + */
> + struct verifier_state st;
> + int insn_idx;
> + int prev_insn_idx;
> + struct verifier_stack_elem *next;
> +};
> +
> +#define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
> +
> +/* single container for all structs
> + * one verifier_env per bpf_check() call
> + */
> +struct verifier_env {
> + struct sk_filter *prog; /* eBPF program being verified */
> + struct verifier_stack_elem *head; /* stack of verifier states to be processed */
> + int stack_size; /* number of states to be processed */
> + struct verifier_state cur_state; /* current verifier state */
> + struct verifier_state_list **branch_landing; /* search prunning optimization */
> + u32 used_maps[MAX_USED_MAPS]; /* array of map_id's used by eBPF program */
> + u32 used_map_cnt; /* number of used maps */
> +};
> +
> +/* verbose verifier prints what it's seeing
> + * bpf_check() is called under map lock, so no race to access this global var
> + */
> +static bool verbose_on;
> +
> +/* when verifier rejects eBPF program, it does a second path with verbose on
> + * to dump the verification trace to the log, so the user can figure out what's
> + * wrong with the program
> + */
> +static int verbose(const char *fmt, ...)
> +{
> + va_list args;
> + int ret;
> +
> + if (!verbose_on)
> + return 0;
> +
> + va_start(args, fmt);
> + ret = vprintk(fmt, args);
> + va_end(args);
> + return ret;
> +}
> +
> +/* string representation of 'enum bpf_reg_type' */
> +static const char * const reg_type_str[] = {
> + [INVALID_PTR] = "inv",
> + [PTR_TO_CTX] = "ctx",
> + [PTR_TO_MAP] = "map_value",
> + [PTR_TO_MAP_CONDITIONAL] = "map_value_or_null",
> + [PTR_TO_STACK] = "fp",
> + [PTR_TO_STACK_IMM] = "fp",
> + [PTR_TO_STACK_IMM_MAP_KEY] = "fp_key",
> + [PTR_TO_STACK_IMM_MAP_VALUE] = "fp_value",
> + [RET_INTEGER] = "ret_int",
> + [RET_VOID] = "ret_void",
> + [CONST_ARG] = "imm",
> + [CONST_ARG_MAP_ID] = "map_id",
> + [CONST_ARG_STACK_IMM_SIZE] = "imm_size",
> +};
> +
> +static void pr_cont_verifier_state(struct verifier_env *env)
> +{
> + enum bpf_reg_type ptr;
> + int i;
> +
> + for (i = 0; i < MAX_BPF_REG; i++) {
> + if (!env->cur_state.regs[i].read_ok)
> + continue;
> + ptr = env->cur_state.regs[i].ptr;
> + pr_cont(" R%d=%s", i, reg_type_str[ptr]);
> + if (ptr == CONST_ARG ||
> + ptr == PTR_TO_STACK_IMM ||
> + ptr == PTR_TO_MAP_CONDITIONAL ||
> + ptr == PTR_TO_MAP)
> + pr_cont("%d", env->cur_state.regs[i].imm);
> + }
> + for (i = 0; i < MAX_BPF_STACK; i++) {
> + if (env->cur_state.stack[i].type == STACK_SPILL)
> + pr_cont(" fp%d=%s", -MAX_BPF_STACK + i,
> + reg_type_str[env->cur_state.stack[i].ptr]);
> + }
> + pr_cont("\n");
> +}
> +
> +static const char *const bpf_class_string[] = {
> + "ld", "ldx", "st", "stx", "alu", "jmp", "BUG", "alu64"
> +};
> +
> +static const char *const bpf_alu_string[] = {
> + "+=", "-=", "*=", "/=", "|=", "&=", "<<=", ">>=", "neg",
> + "%=", "^=", "=", "s>>=", "endian", "BUG", "BUG"
> +};
> +
> +static const char *const bpf_ldst_string[] = {
> + "u32", "u16", "u8", "u64"
> +};
> +
> +static const char *const bpf_jmp_string[] = {
> + "jmp", "==", ">", ">=", "&", "!=", "s>", "s>=", "call", "exit"
> +};
> +
> +static void pr_cont_bpf_insn(struct sock_filter_int *insn)
> +{
> + u8 class = BPF_CLASS(insn->code);
> +
> + if (class == BPF_ALU || class == BPF_ALU64) {
> + if (BPF_SRC(insn->code) == BPF_X)
> + pr_cont("(%02x) %sr%d %s %sr%d\n",
> + insn->code, class == BPF_ALU ? "(u32) " : "",
> + insn->dst_reg,
> + bpf_alu_string[BPF_OP(insn->code) >> 4],
> + class == BPF_ALU ? "(u32) " : "",
> + insn->src_reg);
> + else
> + pr_cont("(%02x) %sr%d %s %s%d\n",
> + insn->code, class == BPF_ALU ? "(u32) " : "",
> + insn->dst_reg,
> + bpf_alu_string[BPF_OP(insn->code) >> 4],
> + class == BPF_ALU ? "(u32) " : "",
> + insn->imm);
> + } else if (class == BPF_STX) {
> + if (BPF_MODE(insn->code) == BPF_MEM)
> + pr_cont("(%02x) *(%s *)(r%d %+d) = r%d\n",
> + insn->code,
> + bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
> + insn->dst_reg,
> + insn->off, insn->src_reg);
> + else if (BPF_MODE(insn->code) == BPF_XADD)
> + pr_cont("(%02x) lock *(%s *)(r%d %+d) += r%d\n",
> + insn->code,
> + bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
> + insn->dst_reg, insn->off,
> + insn->src_reg);
> + else
> + pr_cont("BUG_%02x\n", insn->code);
> + } else if (class == BPF_ST) {
> + if (BPF_MODE(insn->code) != BPF_MEM) {
> + pr_cont("BUG_st_%02x\n", insn->code);
> + return;
> + }
> + pr_cont("(%02x) *(%s *)(r%d %+d) = %d\n",
> + insn->code,
> + bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
> + insn->dst_reg,
> + insn->off, insn->imm);
> + } else if (class == BPF_LDX) {
> + if (BPF_MODE(insn->code) != BPF_MEM) {
> + pr_cont("BUG_ldx_%02x\n", insn->code);
> + return;
> + }
> + pr_cont("(%02x) r%d = *(%s *)(r%d %+d)\n",
> + insn->code, insn->dst_reg,
> + bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
> + insn->src_reg, insn->off);
Can you please add:
+ } else if (class == BPF_LD) {
+ if (BPF_MODE(insn->code) == BPF_ABS) {
+ pr_cont("(%02x) r0 = *(%s *)skb[%d]\n",
+ insn->code,
+ bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
+ insn->imm);
+ } else if (BPF_MODE(insn->code) == BPF_IND) {
+ pr_cont("(%02x) r0 = *(%s *)skb[r%d + %d]\n",
+ insn->code,
+ bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
+ insn->src_reg, insn->imm);
+ } else {
+ pr_cont("BUG_ld_%02x\n", insn->code);
+ return;
+ }
Note that I'm hardcoding r0 (instead of using %d for insn->dst_reg)
because that's how ebpf writes the instructions.
> + } else if (class == BPF_JMP) {
> + u8 opcode = BPF_OP(insn->code);
> +
> + if (opcode == BPF_CALL) {
> + pr_cont("(%02x) call %d\n", insn->code, insn->imm);
> + } else if (insn->code == (BPF_JMP | BPF_JA)) {
> + pr_cont("(%02x) goto pc%+d\n",
> + insn->code, insn->off);
> + } else if (insn->code == (BPF_JMP | BPF_EXIT)) {
> + pr_cont("(%02x) exit\n", insn->code);
> + } else if (BPF_SRC(insn->code) == BPF_X) {
> + pr_cont("(%02x) if r%d %s r%d goto pc%+d\n",
> + insn->code, insn->dst_reg,
> + bpf_jmp_string[BPF_OP(insn->code) >> 4],
> + insn->src_reg, insn->off);
> + } else {
> + pr_cont("(%02x) if r%d %s 0x%x goto pc%+d\n",
> + insn->code, insn->dst_reg,
> + bpf_jmp_string[BPF_OP(insn->code) >> 4],
> + insn->imm, insn->off);
> + }
> + } else {
> + pr_cont("(%02x) %s\n", insn->code, bpf_class_string[class]);
> + }
> +}
> +
> +static int pop_stack(struct verifier_env *env, int *prev_insn_idx)
> +{
> + struct verifier_stack_elem *elem;
> + int insn_idx;
> +
> + if (env->head == NULL)
> + return -1;
> +
> + memcpy(&env->cur_state, &env->head->st, sizeof(env->cur_state));
> + insn_idx = env->head->insn_idx;
> + if (prev_insn_idx)
> + *prev_insn_idx = env->head->prev_insn_idx;
> + elem = env->head->next;
> + kfree(env->head);
> + env->head = elem;
> + env->stack_size--;
> + return insn_idx;
> +}
> +
> +static struct verifier_state *push_stack(struct verifier_env *env, int insn_idx,
> + int prev_insn_idx)
> +{
> + struct verifier_stack_elem *elem;
> +
> + elem = kmalloc(sizeof(struct verifier_stack_elem), GFP_KERNEL);
> + if (!elem)
> + goto err;
> +
> + memcpy(&elem->st, &env->cur_state, sizeof(env->cur_state));
> + elem->insn_idx = insn_idx;
> + elem->prev_insn_idx = prev_insn_idx;
> + elem->next = env->head;
> + env->head = elem;
> + env->stack_size++;
> + if (env->stack_size > 1024) {
> + verbose("BPF program is too complex\n");
> + goto err;
> + }
> + return &elem->st;
> +err:
> + /* pop all elements and return */
> + while (pop_stack(env, NULL) >= 0);
> + return NULL;
> +}
> +
> +#define CALLER_SAVED_REGS 6
> +static const int caller_saved[CALLER_SAVED_REGS] = {
> + BPF_REG_0, BPF_REG_1, BPF_REG_2, BPF_REG_3, BPF_REG_4, BPF_REG_5
> +};
> +
> +static void init_reg_state(struct reg_state *regs)
> +{
> + struct reg_state *reg;
> + int i;
> +
> + for (i = 0; i < MAX_BPF_REG; i++) {
> + regs[i].ptr = INVALID_PTR;
> + regs[i].read_ok = false;
> + regs[i].imm = 0xbadbad;
> + }
> + reg = regs + BPF_REG_FP;
Any reason you switching from the array syntax to the pointer one? I
find "reg = regs[BPF_REG_FP];" more readable (and the one you chose in
the loop).
> + reg->ptr = PTR_TO_STACK;
> + reg->read_ok = true;
> +
> + reg = regs + BPF_REG_1; /* 1st arg to a function */
> + reg->ptr = PTR_TO_CTX;
Wait, doesn't this depend on doing "BPF_MOV64_REG(BPF_REG_CTX,
BPF_REG_ARG1)" (the bpf-to-ebpf prologue), which is only enforced on
filters converted from bpf? In fact, shouldn't this set
regs[BPF_REG_CTX] instead of regs[BPF_REG_1] ?
> + reg->read_ok = true;
> +}
> +
> +static void mark_reg_no_ptr(struct reg_state *regs, int regno)
> +{
> + regs[regno].ptr = INVALID_PTR;
> + regs[regno].imm = 0xbadbad;
> + regs[regno].read_ok = true;
> +}
> +
> +static int check_reg_arg(struct reg_state *regs, int regno, bool is_src)
> +{
> + if (is_src) {
> + if (!regs[regno].read_ok) {
> + verbose("R%d !read_ok\n", regno);
> + return -EACCES;
> + }
> + } else {
> + if (regno == BPF_REG_FP)
> + /* frame pointer is read only */
> + return -EACCES;
> + mark_reg_no_ptr(regs, regno);
> + }
> + return 0;
> +}
> +
> +static int bpf_size_to_bytes(int bpf_size)
> +{
> + if (bpf_size == BPF_W)
> + return 4;
> + else if (bpf_size == BPF_H)
> + return 2;
> + else if (bpf_size == BPF_B)
> + return 1;
> + else if (bpf_size == BPF_DW)
> + return 8;
> + else
> + return -EACCES;
> +}
> +
> +static int check_stack_write(struct verifier_state *state, int off, int size,
> + int value_regno)
> +{
> + struct bpf_stack_slot *slot;
> + int i;
> +
> + if (value_regno >= 0 &&
> + (state->regs[value_regno].ptr == PTR_TO_MAP ||
> + state->regs[value_regno].ptr == PTR_TO_STACK_IMM ||
> + state->regs[value_regno].ptr == PTR_TO_CTX)) {
> +
> + /* register containing pointer is being spilled into stack */
> + if (size != 8) {
> + verbose("invalid size of register spill\n");
> + return -EACCES;
> + }
> +
> + slot = &state->stack[MAX_BPF_STACK + off];
> + slot->type = STACK_SPILL;
> + /* save register state */
> + slot->ptr = state->regs[value_regno].ptr;
> + slot->imm = state->regs[value_regno].imm;
> + for (i = 1; i < 8; i++) {
> + slot = &state->stack[MAX_BPF_STACK + off + i];
> + slot->type = STACK_SPILL_PART;
> + slot->ptr = 0;
> + slot->imm = 0;
> + }
> + } else {
> +
> + /* regular write of data into stack */
> + for (i = 0; i < size; i++) {
> + slot = &state->stack[MAX_BPF_STACK + off + i];
> + slot->type = STACK_MISC;
> + slot->ptr = 0;
> + slot->imm = 0;
> + }
> + }
> + return 0;
> +}
> +
> +static int check_stack_read(struct verifier_state *state, int off, int size,
> + int value_regno)
> +{
> + int i;
> + struct bpf_stack_slot *slot;
> +
> + slot = &state->stack[MAX_BPF_STACK + off];
> +
> + if (slot->type == STACK_SPILL) {
> + if (size != 8) {
> + verbose("invalid size of register spill\n");
> + return -EACCES;
> + }
> + for (i = 1; i < 8; i++) {
> + if (state->stack[MAX_BPF_STACK + off + i].type !=
> + STACK_SPILL_PART) {
> + verbose("corrupted spill memory\n");
> + return -EACCES;
> + }
> + }
> +
> + /* restore register state from stack */
> + state->regs[value_regno].ptr = slot->ptr;
> + state->regs[value_regno].imm = slot->imm;
> + state->regs[value_regno].read_ok = true;
> + return 0;
> + } else {
> + for (i = 0; i < size; i++) {
> + if (state->stack[MAX_BPF_STACK + off + i].type !=
> + STACK_MISC) {
> + verbose("invalid read from stack off %d+%d size %d\n",
> + off, i, size);
> + return -EACCES;
> + }
> + }
> + /* have read misc data from the stack */
> + mark_reg_no_ptr(state->regs, value_regno);
> + return 0;
> + }
> +}
> +
> +static int remember_map_id(struct verifier_env *env, u32 map_id)
> +{
> + int i;
> +
> + /* check whether we recorded this map_id already */
> + for (i = 0; i < env->used_map_cnt; i++)
> + if (env->used_maps[i] == map_id)
> + return 0;
> +
> + if (env->used_map_cnt >= MAX_USED_MAPS)
> + return -E2BIG;
> +
> + /* remember this map_id */
> + env->used_maps[env->used_map_cnt++] = map_id;
> + return 0;
> +}
> +
> +static int get_map_info(struct verifier_env *env, u32 map_id,
> + struct bpf_map **map)
> +{
> + /* if BPF program contains bpf_table_lookup(map_id, key)
> + * the incorrect map_id will be caught here
> + */
> + *map = bpf_map_get(map_id);
> + if (!*map) {
> + verbose("invalid access to map_id=%d\n", map_id);
> + return -EACCES;
> + }
> +
> + _(remember_map_id(env, map_id));
> +
> + return 0;
> +}
> +
> +/* check read/write into map element returned by bpf_table_lookup() */
> +static int check_table_access(struct verifier_env *env, int regno, int off,
> + int size)
> +{
> + struct bpf_map *map;
> + int map_id = env->cur_state.regs[regno].imm;
> +
> + _(get_map_info(env, map_id, &map));
> +
> + if (off < 0 || off + size > map->value_size) {
> + verbose("invalid access to map_id=%d leaf_size=%d off=%d size=%d\n",
> + map_id, map->value_size, off, size);
> + return -EACCES;
> + }
> + return 0;
> +}
> +
> +/* check access to 'struct bpf_context' fields */
> +static int check_ctx_access(struct verifier_env *env, int off, int size,
> + enum bpf_access_type t)
> +{
> + if (env->prog->info->ops->is_valid_access &&
> + env->prog->info->ops->is_valid_access(off, size, t))
> + return 0;
> +
> + verbose("invalid bpf_context access off=%d size=%d\n", off, size);
> + return -EACCES;
> +}
> +
> +static int check_mem_access(struct verifier_env *env, int regno, int off,
> + int bpf_size, enum bpf_access_type t,
> + int value_regno)
> +{
> + struct verifier_state *state = &env->cur_state;
> + int size;
> +
> + _(size = bpf_size_to_bytes(bpf_size));
> +
> + if (off % size != 0) {
> + verbose("misaligned access off %d size %d\n", off, size);
> + return -EACCES;
> + }
> +
> + if (state->regs[regno].ptr == PTR_TO_MAP) {
> + _(check_table_access(env, regno, off, size));
> + if (t == BPF_READ)
> + mark_reg_no_ptr(state->regs, value_regno);
> + } else if (state->regs[regno].ptr == PTR_TO_CTX) {
> + _(check_ctx_access(env, off, size, t));
> + if (t == BPF_READ)
> + mark_reg_no_ptr(state->regs, value_regno);
> + } else if (state->regs[regno].ptr == PTR_TO_STACK) {
> + if (off >= 0 || off < -MAX_BPF_STACK) {
> + verbose("invalid stack off=%d size=%d\n", off, size);
> + return -EACCES;
> + }
> + if (t == BPF_WRITE)
> + _(check_stack_write(state, off, size, value_regno));
> + else
> + _(check_stack_read(state, off, size, value_regno));
> + } else {
> + verbose("R%d invalid mem access '%s'\n",
> + regno, reg_type_str[state->regs[regno].ptr]);
> + return -EACCES;
> + }
> + return 0;
> +}
> +
> +/* when register 'regno' is passed into function that will read 'access_size'
> + * bytes from that pointer, make sure that it's within stack boundary
> + * and all elements of stack are initialized
> + */
> +static int check_stack_boundary(struct verifier_env *env,
> + int regno, int access_size)
> +{
> + struct verifier_state *state = &env->cur_state;
> + struct reg_state *regs = state->regs;
> + int off, i;
> +
> + if (regs[regno].ptr != PTR_TO_STACK_IMM)
> + return -EACCES;
> +
> + off = regs[regno].imm;
> + if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 ||
> + access_size <= 0) {
> + verbose("invalid stack ptr R%d off=%d access_size=%d\n",
> + regno, off, access_size);
> + return -EACCES;
> + }
> +
> + for (i = 0; i < access_size; i++) {
> + if (state->stack[MAX_BPF_STACK + off + i].type != STACK_MISC) {
> + verbose("invalid indirect read from stack off %d+%d size %d\n",
> + off, i, access_size);
> + return -EACCES;
> + }
> + }
> + return 0;
> +}
> +
> +static int check_func_arg(struct verifier_env *env, int regno,
> + enum bpf_reg_type arg_type, int *map_id,
> + struct bpf_map **mapp)
> +{
> + struct reg_state *reg = env->cur_state.regs + regno;
> + enum bpf_reg_type expected_type;
> +
> + if (arg_type == INVALID_PTR)
> + return 0;
> +
> + if (!reg->read_ok) {
> + verbose("R%d !read_ok\n", regno);
> + return -EACCES;
> + }
> +
> + if (arg_type == PTR_TO_STACK_IMM_MAP_KEY ||
> + arg_type == PTR_TO_STACK_IMM_MAP_VALUE)
> + expected_type = PTR_TO_STACK_IMM;
> + else if (arg_type == CONST_ARG_MAP_ID ||
> + arg_type == CONST_ARG_STACK_IMM_SIZE)
> + expected_type = CONST_ARG;
> + else
> + expected_type = arg_type;
> +
> + if (reg->ptr != expected_type) {
> + verbose("R%d type=%s expected=%s\n", regno,
> + reg_type_str[reg->ptr], reg_type_str[expected_type]);
> + return -EACCES;
> + }
> +
> + if (arg_type == CONST_ARG_MAP_ID) {
> + /* bpf_map_xxx(map_id) call: check that map_id is valid */
> + *map_id = reg->imm;
> + _(get_map_info(env, reg->imm, mapp));
> + } else if (arg_type == PTR_TO_STACK_IMM_MAP_KEY) {
> + /*
> + * bpf_map_xxx(..., map_id, ..., key) call:
> + * check that [key, key + map->key_size) are within
> + * stack limits and initialized
> + */
> + if (!*mapp) {
> + /*
> + * in function declaration map_id must come before
> + * table_key or table_elem, so that it's verified
> + * and known before we have to check table_key here
> + */
> + verbose("invalid map_id to access map->key\n");
> + return -EACCES;
> + }
> + _(check_stack_boundary(env, regno, (*mapp)->key_size));
> + } else if (arg_type == PTR_TO_STACK_IMM_MAP_VALUE) {
> + /*
> + * bpf_map_xxx(..., map_id, ..., value) call:
> + * check [value, value + map->value_size) validity
> + */
> + if (!*mapp) {
> + verbose("invalid map_id to access map->elem\n");
> + return -EACCES;
> + }
> + _(check_stack_boundary(env, regno, (*mapp)->value_size));
> + } else if (arg_type == CONST_ARG_STACK_IMM_SIZE) {
> + /*
> + * bpf_xxx(..., buf, len) call will access 'len' bytes
> + * from stack pointer 'buf'. Check it
> + * note: regno == len, regno - 1 == buf
> + */
> + _(check_stack_boundary(env, regno - 1, reg->imm));
> + }
> +
> + return 0;
> +}
> +
> +static int check_call(struct verifier_env *env, int func_id)
> +{
> + struct verifier_state *state = &env->cur_state;
> + const struct bpf_func_proto *fn = NULL;
> + struct reg_state *regs = state->regs;
> + struct bpf_map *map = NULL;
> + struct reg_state *reg;
> + int map_id = -1;
> + int i;
> +
> + /* find function prototype */
> + if (func_id <= 0 || func_id >= __BPF_FUNC_MAX_ID) {
> + verbose("invalid func %d\n", func_id);
> + return -EINVAL;
> + }
> +
> + if (env->prog->info->ops->get_func_proto)
> + fn = env->prog->info->ops->get_func_proto(func_id);
> +
> + if (!fn || (fn->ret_type != RET_INTEGER &&
> + fn->ret_type != PTR_TO_MAP_CONDITIONAL &&
> + fn->ret_type != RET_VOID)) {
> + verbose("unknown func %d\n", func_id);
> + return -EINVAL;
> + }
> +
> + /* check args */
> + _(check_func_arg(env, BPF_REG_1, fn->arg1_type, &map_id, &map));
> + _(check_func_arg(env, BPF_REG_2, fn->arg2_type, &map_id, &map));
> + _(check_func_arg(env, BPF_REG_3, fn->arg3_type, &map_id, &map));
> + _(check_func_arg(env, BPF_REG_4, fn->arg4_type, &map_id, &map));
> +
> + /* reset caller saved regs */
> + for (i = 0; i < CALLER_SAVED_REGS; i++) {
> + reg = regs + caller_saved[i];
> + reg->read_ok = false;
> + reg->ptr = INVALID_PTR;
> + reg->imm = 0xbadbad;
> + }
> +
> + /* update return register */
> + reg = regs + BPF_REG_0;
> + if (fn->ret_type == RET_INTEGER) {
> + reg->read_ok = true;
> + reg->ptr = INVALID_PTR;
> + } else if (fn->ret_type != RET_VOID) {
> + reg->read_ok = true;
> + reg->ptr = fn->ret_type;
> + if (fn->ret_type == PTR_TO_MAP_CONDITIONAL)
> + /*
> + * remember map_id, so that check_table_access()
> + * can check 'value_size' boundary of memory access
> + * to map element returned from bpf_table_lookup()
> + */
> + reg->imm = map_id;
> + }
> + return 0;
> +}
> +
> +/* check validity of 32-bit and 64-bit arithmetic operations */
> +static int check_alu_op(struct reg_state *regs, struct sock_filter_int *insn)
> +{
> + u8 opcode = BPF_OP(insn->code);
> +
> + if (opcode == BPF_END || opcode == BPF_NEG) {
> + if (BPF_SRC(insn->code) != BPF_X)
> + return -EINVAL;
> + /* check src operand */
> + _(check_reg_arg(regs, insn->dst_reg, 1));
> +
> + /* check dest operand */
> + _(check_reg_arg(regs, insn->dst_reg, 0));
> +
> + } else if (opcode == BPF_MOV) {
> +
> + if (BPF_SRC(insn->code) == BPF_X)
> + /* check src operand */
> + _(check_reg_arg(regs, insn->src_reg, 1));
> +
> + /* check dest operand */
> + _(check_reg_arg(regs, insn->dst_reg, 0));
> +
> + if (BPF_SRC(insn->code) == BPF_X) {
> + if (BPF_CLASS(insn->code) == BPF_ALU64) {
> + /* case: R1 = R2
> + * copy register state to dest reg
> + */
> + regs[insn->dst_reg].ptr = regs[insn->src_reg].ptr;
> + regs[insn->dst_reg].imm = regs[insn->src_reg].imm;
> + } else {
> + regs[insn->dst_reg].ptr = INVALID_PTR;
> + regs[insn->dst_reg].imm = 0;
> + }
> + } else {
> + /* case: R = imm
> + * remember the value we stored into this reg
> + */
> + regs[insn->dst_reg].ptr = CONST_ARG;
> + regs[insn->dst_reg].imm = insn->imm;
> + }
> +
> + } else { /* all other ALU ops: and, sub, xor, add, ... */
> +
> + int stack_relative = 0;
> +
> + if (BPF_SRC(insn->code) == BPF_X)
> + /* check src1 operand */
> + _(check_reg_arg(regs, insn->src_reg, 1));
> +
> + /* check src2 operand */
> + _(check_reg_arg(regs, insn->dst_reg, 1));
> +
> + if (opcode == BPF_ADD && BPF_CLASS(insn->code) == BPF_ALU64 &&
> + regs[insn->dst_reg].ptr == PTR_TO_STACK &&
> + BPF_SRC(insn->code) == BPF_K)
> + stack_relative = 1;
> +
> + /* check dest operand */
> + _(check_reg_arg(regs, insn->dst_reg, 0));
> +
> + if (stack_relative) {
> + regs[insn->dst_reg].ptr = PTR_TO_STACK_IMM;
> + regs[insn->dst_reg].imm = insn->imm;
> + }
> + }
> +
> + return 0;
> +}
> +
> +static int check_cond_jmp_op(struct verifier_env *env,
> + struct sock_filter_int *insn, int *insn_idx)
> +{
> + struct reg_state *regs = env->cur_state.regs;
> + struct verifier_state *other_branch;
> + u8 opcode = BPF_OP(insn->code);
> +
> + if (BPF_SRC(insn->code) == BPF_X)
> + /* check src1 operand */
> + _(check_reg_arg(regs, insn->src_reg, 1));
> +
> + /* check src2 operand */
> + _(check_reg_arg(regs, insn->dst_reg, 1));
> +
> + /* detect if R == 0 where R was initialized to zero earlier */
> + if (BPF_SRC(insn->code) == BPF_K &&
> + (opcode == BPF_JEQ || opcode == BPF_JNE) &&
> + regs[insn->dst_reg].ptr == CONST_ARG &&
> + regs[insn->dst_reg].imm == insn->imm) {
> + if (opcode == BPF_JEQ) {
> + /* if (imm == imm) goto pc+off;
> + * only follow the goto, ignore fall-through
> + */
> + *insn_idx += insn->off;
> + return 0;
> + } else {
> + /* if (imm != imm) goto pc+off;
> + * only follow fall-through branch, since
> + * that's where the program will go
> + */
> + return 0;
> + }
> + }
> +
> + other_branch = push_stack(env, *insn_idx + insn->off + 1, *insn_idx);
> + if (!other_branch)
> + return -EFAULT;
> +
> + /* detect if R == 0 where R is returned value from table_lookup() */
> + if (BPF_SRC(insn->code) == BPF_K &&
> + insn->imm == 0 && (opcode == BPF_JEQ ||
> + opcode == BPF_JNE) &&
> + regs[insn->dst_reg].ptr == PTR_TO_MAP_CONDITIONAL) {
> + if (opcode == BPF_JEQ) {
> + /* next fallthrough insn can access memory via
> + * this register
> + */
> + regs[insn->dst_reg].ptr = PTR_TO_MAP;
> + /* branch targer cannot access it, since reg == 0 */
> + other_branch->regs[insn->dst_reg].ptr = CONST_ARG;
> + other_branch->regs[insn->dst_reg].imm = 0;
> + } else {
> + other_branch->regs[insn->dst_reg].ptr = PTR_TO_MAP;
> + regs[insn->dst_reg].ptr = CONST_ARG;
> + regs[insn->dst_reg].imm = 0;
> + }
> + } else if (BPF_SRC(insn->code) == BPF_K &&
> + (opcode == BPF_JEQ || opcode == BPF_JNE)) {
> +
> + if (opcode == BPF_JEQ) {
> + /* detect if (R == imm) goto
> + * and in the target state recognize that R = imm
> + */
> + other_branch->regs[insn->dst_reg].ptr = CONST_ARG;
> + other_branch->regs[insn->dst_reg].imm = insn->imm;
> + } else {
> + /* detect if (R != imm) goto
> + * and in the fall-through state recognize that R = imm
> + */
> + regs[insn->dst_reg].ptr = CONST_ARG;
> + regs[insn->dst_reg].imm = insn->imm;
> + }
> + }
> + if (verbose_on)
> + pr_cont_verifier_state(env);
> + return 0;
> +}
> +
> +/* verify safety of LD_ABS|LD_IND instructions:
> + * - they can only appear in the programs where ctx == skb
> + * - since they are wrappers of function calls, they scratch R1-R5 registers,
> + * preserve R6-R9, and store return value into R0
> + *
> + * Implicit input:
> + * ctx == skb == R6 == CTX
> + *
> + * Explicit input:
> + * SRC == any register
> + * IMM == 32-bit immediate
> + *
> + * Output:
> + * R0 - 8/16/32-bit skb data converted to cpu endianness
> + */
> +
> +static int check_ld_abs(struct verifier_env *env, struct sock_filter_int *insn)
> +{
> + struct reg_state *regs = env->cur_state.regs;
> + u8 mode = BPF_MODE(insn->code);
> + struct reg_state *reg;
> + int i;
> +
> + if (mode != BPF_ABS && mode != BPF_IND)
> + return -EINVAL;
> +
> + if (env->prog->info->prog_type != BPF_PROG_TYPE_SOCKET_FILTER) {
> + verbose("BPF_LD_ABS|IND instructions are only allowed in socket filters\n");
> + return -EINVAL;
> + }
> +
> + /* check whether implicit source operand (register R6) is readable */
> + _(check_reg_arg(regs, BPF_REG_6, 1));
> +
> + if (regs[BPF_REG_6].ptr != PTR_TO_CTX) {
> + verbose("at the time of BPF_LD_ABS|IND R6 != pointer to skb\n");
> + return -EINVAL;
> + }
> +
> + if (mode == BPF_IND)
> + /* check explicit source operand */
> + _(check_reg_arg(regs, insn->src_reg, 1));
> +
> + /* reset caller saved regs to unreadable */
> + for (i = 0; i < CALLER_SAVED_REGS; i++) {
> + reg = regs + caller_saved[i];
> + reg->read_ok = false;
> + reg->ptr = INVALID_PTR;
> + reg->imm = 0xbadbad;
> + }
> +
> + /* mark destination R0 register as readable, since it contains
> + * the value fetched from the packet
> + */
> + regs[BPF_REG_0].read_ok = true;
> + return 0;
> +}
> +
> +/* non-recursive DFS pseudo code
> + * 1 procedure DFS-iterative(G,v):
> + * 2 label v as discovered
> + * 3 let S be a stack
> + * 4 S.push(v)
> + * 5 while S is not empty
> + * 6 t <- S.pop()
> + * 7 if t is what we're looking for:
> + * 8 return t
> + * 9 for all edges e in G.adjacentEdges(t) do
> + * 10 if edge e is already labelled
> + * 11 continue with the next edge
> + * 12 w <- G.adjacentVertex(t,e)
> + * 13 if vertex w is not discovered and not explored
> + * 14 label e as tree-edge
> + * 15 label w as discovered
> + * 16 S.push(w)
> + * 17 continue at 5
> + * 18 else if vertex w is discovered
> + * 19 label e as back-edge
> + * 20 else
> + * 21 // vertex w is explored
> + * 22 label e as forward- or cross-edge
> + * 23 label t as explored
> + * 24 S.pop()
> + *
> + * convention:
> + * 1 - discovered
> + * 2 - discovered and 1st branch labelled
> + * 3 - discovered and 1st and 2nd branch labelled
> + * 4 - explored
> + */
> +
> +#define STATE_END ((struct verifier_state_list *)-1)
> +
> +#define PUSH_INT(I) \
> + do { \
> + if (cur_stack >= insn_cnt) { \
> + ret = -E2BIG; \
> + goto free_st; \
> + } \
> + stack[cur_stack++] = I; \
> + } while (0)
> +
> +#define PEAK_INT() \
> + ({ \
> + int _ret; \
> + if (cur_stack == 0) \
> + _ret = -1; \
> + else \
> + _ret = stack[cur_stack - 1]; \
> + _ret; \
> + })
> +
> +#define POP_INT() \
> + ({ \
> + int _ret; \
> + if (cur_stack == 0) \
> + _ret = -1; \
> + else \
> + _ret = stack[--cur_stack]; \
> + _ret; \
> + })
> +
> +#define PUSH_INSN(T, W, E) \
> + do { \
> + int w = W; \
> + if (E == 1 && st[T] >= 2) \
> + break; \
> + if (E == 2 && st[T] >= 3) \
> + break; \
> + if (w >= insn_cnt) { \
> + ret = -EACCES; \
> + goto free_st; \
> + } \
> + if (E == 2) \
> + /* mark branch target for state pruning */ \
> + env->branch_landing[w] = STATE_END; \
> + if (st[w] == 0) { \
> + /* tree-edge */ \
> + st[T] = 1 + E; \
> + st[w] = 1; /* discovered */ \
> + PUSH_INT(w); \
> + goto peak_stack; \
> + } else if (st[w] == 1 || st[w] == 2 || st[w] == 3) { \
> + verbose("back-edge from insn %d to %d\n", t, w); \
> + ret = -EINVAL; \
> + goto free_st; \
> + } else if (st[w] == 4) { \
> + /* forward- or cross-edge */ \
> + st[T] = 1 + E; \
> + } else { \
> + verbose("insn state internal bug\n"); \
> + ret = -EFAULT; \
> + goto free_st; \
> + } \
> + } while (0)
> +
> +/* non-recursive depth-first-search to detect loops in BPF program
> + * loop == back-edge in directed graph
> + */
> +static int check_cfg(struct verifier_env *env)
> +{
> + struct sock_filter_int *insns = env->prog->insnsi;
> + int insn_cnt = env->prog->len;
> + int cur_stack = 0;
> + int *stack;
> + int ret = 0;
> + int *st;
> + int i, t;
> +
> + if (insns[insn_cnt - 1].code != (BPF_JMP | BPF_EXIT)) {
> + verbose("last insn is not a 'ret'\n");
> + return -EINVAL;
> + }
> +
> + st = kzalloc(sizeof(int) * insn_cnt, GFP_KERNEL);
> + if (!st)
> + return -ENOMEM;
> +
> + stack = kzalloc(sizeof(int) * insn_cnt, GFP_KERNEL);
> + if (!stack) {
> + kfree(st);
> + return -ENOMEM;
> + }
> +
> + st[0] = 1; /* mark 1st insn as discovered */
> + PUSH_INT(0);
> +
> +peak_stack:
> + while ((t = PEAK_INT()) != -1) {
> + if (insns[t].code == (BPF_JMP | BPF_EXIT))
> + goto mark_explored;
> +
> + if (BPF_CLASS(insns[t].code) == BPF_JMP) {
> + u8 opcode = BPF_OP(insns[t].code);
> +
> + if (opcode == BPF_CALL) {
> + PUSH_INSN(t, t + 1, 1);
> + } else if (opcode == BPF_JA) {
> + if (BPF_SRC(insns[t].code) != BPF_X) {
> + ret = -EINVAL;
> + goto free_st;
> + }
> + PUSH_INSN(t, t + insns[t].off + 1, 1);
> + } else {
> + PUSH_INSN(t, t + 1, 1);
> + PUSH_INSN(t, t + insns[t].off + 1, 2);
> + }
> + /* tell verifier to check for equivalent verifier states
> + * after every call and jump
> + */
> + env->branch_landing[t + 1] = STATE_END;
> + } else {
> + PUSH_INSN(t, t + 1, 1);
> + }
> +
> +mark_explored:
> + st[t] = 4; /* explored */
> + if (POP_INT() == -1) {
> + verbose("pop_int internal bug\n");
> + ret = -EFAULT;
> + goto free_st;
> + }
> + }
> +
> +
> + for (i = 0; i < insn_cnt; i++) {
> + if (st[i] != 4) {
> + verbose("unreachable insn %d\n", i);
> + ret = -EINVAL;
> + goto free_st;
> + }
> + }
> +
> +free_st:
> + kfree(st);
> + kfree(stack);
> + return ret;
> +}
> +
> +/* compare two verifier states
> + *
> + * all states stored in state_list are known to be valid, since
> + * verifier reached 'bpf_exit' instruction through them
> + *
> + * this function is called when verifier exploring different branches of
> + * execution popped from the state stack. If it sees an old state that has
> + * more strict register state and more strict stack state then this execution
> + * branch doesn't need to be explored further, since verifier already
> + * concluded that more strict state leads to valid finish.
> + *
> + * Therefore two states are equivalent if register state is more conservative
> + * and explored stack state is more conservative than the current one.
> + * Example:
> + * explored current
> + * (slot1=INV slot2=MISC) == (slot1=MISC slot2=MISC)
> + * (slot1=MISC slot2=MISC) != (slot1=INV slot2=MISC)
> + *
> + * In other words if current stack state (one being explored) has more
> + * valid slots than old one that already passed validation, it means
> + * the verifier can stop exploring and conclude that current state is valid too
> + *
> + * Similarly with registers. If explored state has register type as invalid
> + * whereas register type in current state is meaningful, it means that
> + * the current state will reach 'bpf_exit' instruction safely
> + */
> +static bool states_equal(struct verifier_state *old, struct verifier_state *cur)
> +{
> + int i;
> +
> + for (i = 0; i < MAX_BPF_REG; i++) {
> + if (memcmp(&old->regs[i], &cur->regs[i],
> + sizeof(old->regs[0])) != 0) {
> + if (!old->regs[i].read_ok)
> + continue;
> + if (old->regs[i].ptr == INVALID_PTR)
> + continue;
> + return false;
> + }
> + }
> +
> + for (i = 0; i < MAX_BPF_STACK; i++) {
> + if (memcmp(&old->stack[i], &cur->stack[i],
> + sizeof(old->stack[0])) != 0) {
> + if (old->stack[i].type == STACK_INVALID)
> + continue;
> + return false;
> + }
> + }
> + return true;
> +}
> +
> +static int is_state_visited(struct verifier_env *env, int insn_idx)
> +{
> + struct verifier_state_list *new_sl;
> + struct verifier_state_list *sl;
> +
> + sl = env->branch_landing[insn_idx];
> + if (!sl)
> + /* no branch jump to this insn, ignore it */
> + return 0;
> +
> + while (sl != STATE_END) {
> + if (states_equal(&sl->state, &env->cur_state))
> + /* reached equivalent register/stack state,
> + * prune the search
> + */
> + return 1;
> + sl = sl->next;
> + }
> + new_sl = kmalloc(sizeof(struct verifier_state_list), GFP_KERNEL);
> +
> + if (!new_sl)
> + /* ignore ENOMEM, it doesn't affect correctness */
> + return 0;
> +
> + /* add new state to the head of linked list */
> + memcpy(&new_sl->state, &env->cur_state, sizeof(env->cur_state));
> + new_sl->next = env->branch_landing[insn_idx];
> + env->branch_landing[insn_idx] = new_sl;
> + return 0;
> +}
> +
> +static int do_check(struct verifier_env *env)
> +{
> + struct verifier_state *state = &env->cur_state;
> + struct sock_filter_int *insns = env->prog->insnsi;
> + struct reg_state *regs = state->regs;
> + int insn_cnt = env->prog->len;
> + int insn_idx, prev_insn_idx = 0;
> + int insn_processed = 0;
> + bool do_print_state = false;
> +
> + init_reg_state(regs);
> + insn_idx = 0;
> + for (;;) {
> + struct sock_filter_int *insn;
> + u8 class;
> +
> + if (insn_idx >= insn_cnt) {
> + verbose("invalid insn idx %d insn_cnt %d\n",
> + insn_idx, insn_cnt);
> + return -EFAULT;
> + }
> +
> + insn = &insns[insn_idx];
> + class = BPF_CLASS(insn->code);
> +
> + if (++insn_processed > 32768) {
> + verbose("BPF program is too large. Proccessed %d insn\n",
> + insn_processed);
> + return -E2BIG;
> + }
> +
> + if (is_state_visited(env, insn_idx)) {
> + if (verbose_on) {
> + if (do_print_state)
> + pr_cont("\nfrom %d to %d: safe\n",
> + prev_insn_idx, insn_idx);
> + else
> + pr_cont("%d: safe\n", insn_idx);
> + }
> + goto process_bpf_exit;
> + }
> +
> + if (verbose_on && do_print_state) {
> + pr_cont("\nfrom %d to %d:", prev_insn_idx, insn_idx);
> + pr_cont_verifier_state(env);
> + do_print_state = false;
> + }
> +
> + if (verbose_on) {
> + pr_cont("%d: ", insn_idx);
> + pr_cont_bpf_insn(insn);
> + }
> +
> + if (class == BPF_ALU || class == BPF_ALU64) {
> + _(check_alu_op(regs, insn));
> +
> + } else if (class == BPF_LDX) {
> + if (BPF_MODE(insn->code) != BPF_MEM)
> + return -EINVAL;
> +
> + /* check src operand */
> + _(check_reg_arg(regs, insn->src_reg, 1));
> +
> + _(check_mem_access(env, insn->src_reg, insn->off,
> + BPF_SIZE(insn->code), BPF_READ,
> + insn->dst_reg));
> +
> + /* dest reg state will be updated by mem_access */
> +
> + } else if (class == BPF_STX) {
> + /* check src1 operand */
> + _(check_reg_arg(regs, insn->src_reg, 1));
> + /* check src2 operand */
> + _(check_reg_arg(regs, insn->dst_reg, 1));
> + _(check_mem_access(env, insn->dst_reg, insn->off,
> + BPF_SIZE(insn->code), BPF_WRITE,
> + insn->src_reg));
> +
> + } else if (class == BPF_ST) {
> + if (BPF_MODE(insn->code) != BPF_MEM)
> + return -EINVAL;
> + /* check src operand */
> + _(check_reg_arg(regs, insn->dst_reg, 1));
> + _(check_mem_access(env, insn->dst_reg, insn->off,
> + BPF_SIZE(insn->code), BPF_WRITE,
> + -1));
> +
> + } else if (class == BPF_JMP) {
> + u8 opcode = BPF_OP(insn->code);
> +
> + if (opcode == BPF_CALL) {
> + _(check_call(env, insn->imm));
> + } else if (opcode == BPF_JA) {
> + if (BPF_SRC(insn->code) != BPF_X)
> + return -EINVAL;
> + insn_idx += insn->off + 1;
> + continue;
> + } else if (opcode == BPF_EXIT) {
> + /* eBPF calling convetion is such that R0 is used
> + * to return the value from eBPF program.
> + * Make sure that it's readable at this time
> + * of bpf_exit, which means that program wrote
> + * something into it earlier
> + */
> + _(check_reg_arg(regs, BPF_REG_0, 1));
> +process_bpf_exit:
> + insn_idx = pop_stack(env, &prev_insn_idx);
> + if (insn_idx < 0) {
> + break;
> + } else {
> + do_print_state = true;
> + continue;
> + }
> + } else {
> + _(check_cond_jmp_op(env, insn, &insn_idx));
> + }
> + } else if (class == BPF_LD) {
> + _(check_ld_abs(env, insn));
> + } else {
> + verbose("unknown insn class %d\n", class);
> + return -EINVAL;
> + }
> +
> + insn_idx++;
> + }
> +
> + return 0;
> +}
> +
> +static void free_states(struct verifier_env *env, int insn_cnt)
> +{
> + struct verifier_state_list *sl, *sln;
> + int i;
> +
> + for (i = 0; i < insn_cnt; i++) {
> + sl = env->branch_landing[i];
> +
> + if (sl)
> + while (sl != STATE_END) {
> + sln = sl->next;
> + kfree(sl);
> + sl = sln;
> + }
> + }
> +
> + kfree(env->branch_landing);
> +}
> +
> +int bpf_check(struct sk_filter *prog)
> +{
> + struct verifier_env *env;
> + int ret;
> +
> + if (prog->len <= 0 || prog->len > BPF_MAXINSNS)
> + return -E2BIG;
> +
> + env = kzalloc(sizeof(struct verifier_env), GFP_KERNEL);
> + if (!env)
> + return -ENOMEM;
> +
> + verbose_on = false;
> +retry:
> + env->prog = prog;
> + env->branch_landing = kcalloc(prog->len,
> + sizeof(struct verifier_state_list *),
> + GFP_KERNEL);
> +
> + if (!env->branch_landing) {
> + kfree(env);
> + return -ENOMEM;
> + }
> +
> + ret = check_cfg(env);
> + if (ret < 0)
> + goto free_env;
> +
> + ret = do_check(env);
> +
> +free_env:
> + while (pop_stack(env, NULL) >= 0);
> + free_states(env, prog->len);
> +
> + if (ret < 0 && !verbose_on && capable(CAP_SYS_ADMIN)) {
> + /* verification failed, redo it with verbose on */
> + memset(env, 0, sizeof(struct verifier_env));
> + verbose_on = true;
> + goto retry;
> + }
> +
> + if (ret == 0 && env->used_map_cnt) {
> + /* if program passed verifier, update used_maps in bpf_prog_info */
> + prog->info->used_maps = kmalloc_array(env->used_map_cnt,
> + sizeof(u32), GFP_KERNEL);
> + if (!prog->info->used_maps) {
> + kfree(env);
> + return -ENOMEM;
> + }
> + memcpy(prog->info->used_maps, env->used_maps,
> + sizeof(u32) * env->used_map_cnt);
> + prog->info->used_map_cnt = env->used_map_cnt;
> + }
> +
> + kfree(env);
> + return ret;
> +}
> --
> 1.7.9.5
>
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