This patch adds the bulk of the verifier work for supporting dynamic
pointers (dynptrs) in bpf.
A bpf_dynptr is opaque to the bpf program. It is a 16-byte structure
defined internally as:
struct bpf_dynptr_kern {
void *data;
u32 size;
u32 offset;
} __aligned(8);
The upper 8 bits of *size* is reserved (it contains extra metadata about
read-only status and dynptr type). Consequently, a dynptr only supports
memory less than 16 MB.
There are different types of dynptrs (eg malloc, ringbuf, ...). In this
patchset, the most basic one, dynptrs to a bpf program's local memory,
is added. For now only local memory that is of reg type PTR_TO_MAP_VALUE
is supported.
In the verifier, dynptr state information will be tracked in stack
slots. When the program passes in an uninitialized dynptr
(ARG_PTR_TO_DYNPTR | MEM_UNINIT), the stack slots corresponding
to the frame pointer where the dynptr resides at are marked
STACK_DYNPTR. For helper functions that take in initialized dynptrs (eg
bpf_dynptr_read + bpf_dynptr_write which are added later in this
patchset), the verifier enforces that the dynptr has been initialized
properly by checking that their corresponding stack slots have been
marked as STACK_DYNPTR.
The 6th patch in this patchset adds test cases that the verifier should
successfully reject, such as for example attempting to use a dynptr
after doing a direct write into it inside the bpf program.
Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Acked-by: David Vernet <void@xxxxxxxxxxxxx>
---
include/linux/bpf.h | 28 +++++
include/linux/bpf_verifier.h | 18 ++++
include/uapi/linux/bpf.h | 5 +
kernel/bpf/verifier.c | 188 ++++++++++++++++++++++++++++++++-
scripts/bpf_doc.py | 2 +
tools/include/uapi/linux/bpf.h | 5 +
6 files changed, 243 insertions(+), 3 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cc4d5e394031..f5ff04a2da2a 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -392,10 +392,15 @@ enum bpf_type_flag {
MEM_UNINIT = BIT(7 + BPF_BASE_TYPE_BITS),
+ /* DYNPTR points to memory local to the bpf program. */
+ DYNPTR_TYPE_LOCAL = BIT(8 + BPF_BASE_TYPE_BITS),
+
__BPF_TYPE_FLAG_MAX,
__BPF_TYPE_LAST_FLAG = __BPF_TYPE_FLAG_MAX - 1,
};
+#define DYNPTR_TYPE_FLAG_MASK DYNPTR_TYPE_LOCAL
+
/* Max number of base types. */
#define BPF_BASE_TYPE_LIMIT (1UL << BPF_BASE_TYPE_BITS)
@@ -438,6 +443,7 @@ enum bpf_arg_type {
ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only string */
ARG_PTR_TO_TIMER, /* pointer to bpf_timer */
ARG_PTR_TO_KPTR, /* pointer to referenced kptr */
+ ARG_PTR_TO_DYNPTR, /* pointer to bpf_dynptr. See bpf_type_flag for dynptr type */
__BPF_ARG_TYPE_MAX,
/* Extended arg_types. */
@@ -2375,4 +2381,26 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
u32 **bin_buf, u32 num_args);
void bpf_bprintf_cleanup(void);
+/* the implementation of the opaque uapi struct bpf_dynptr */
+struct bpf_dynptr_kern {
+ void *data;
+ /* Size represents the number of usable bytes of dynptr data.
+ * If for example the offset is at 4 for a local dynptr whose data is
+ * of type u64, the number of usable bytes is 4.
+ *
+ * The upper 8 bits are reserved. It is as follows:
+ * Bits 0 - 23 = size
+ * Bits 24 - 30 = dynptr type
+ * Bit 31 = whether dynptr is read-only
+ */
+ u32 size;
+ u32 offset;
+} __aligned(8);
+
+enum bpf_dynptr_type {
+ BPF_DYNPTR_TYPE_INVALID,
+ /* Points to memory that is local to the bpf program */
+ BPF_DYNPTR_TYPE_LOCAL,
+};
+
#endif /* _LINUX_BPF_H */
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 1f1e7f2ea967..af5b2135215e 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -72,6 +72,18 @@ struct bpf_reg_state {
u32 mem_size; /* for PTR_TO_MEM | PTR_TO_MEM_OR_NULL */
+ /* For dynptr stack slots */
+ struct {
+ enum bpf_dynptr_type type;
+ /* A dynptr is 16 bytes so it takes up 2 stack slots.
+ * We need to track which slot is the first slot
+ * to protect against cases where the user may try to
+ * pass in an address starting at the second slot of the
+ * dynptr.
+ */
+ bool first_slot;
+ } dynptr;
+
/* Max size from any of the above. */
struct {
unsigned long raw1;
@@ -174,9 +186,15 @@ enum bpf_stack_slot_type {
STACK_SPILL, /* register spilled into stack */
STACK_MISC, /* BPF program wrote some data into this slot */
STACK_ZERO, /* BPF program wrote constant zero */
+ /* A dynptr is stored in this stack slot. The type of dynptr
+ * is stored in bpf_stack_state->spilled_ptr.dynptr.type
+ */
+ STACK_DYNPTR,
};
#define BPF_REG_SIZE 8 /* size of eBPF register in bytes */
+#define BPF_DYNPTR_SIZE sizeof(struct bpf_dynptr_kern)
+#define BPF_DYNPTR_NR_SLOTS (BPF_DYNPTR_SIZE / BPF_REG_SIZE)
struct bpf_stack_state {
struct bpf_reg_state spilled_ptr;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 56688bee20d9..610944cb3389 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6528,6 +6528,11 @@ struct bpf_timer {
__u64 :64;
} __attribute__((aligned(8)));
+struct bpf_dynptr {
+ __u64 :64;
+ __u64 :64;
+} __attribute__((aligned(8)));
+
struct bpf_sysctl {
__u32 write; /* Sysctl is being read (= 0) or written (= 1).
* Allows 1,2,4-byte read, but no write.
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 14e8c17d3d8d..68bf16cda415 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -259,6 +259,7 @@ struct bpf_call_arg_meta {
u32 ret_btf_id;
u32 subprogno;
struct bpf_map_value_off_desc *kptr_off_desc;
+ u8 uninit_dynptr_regno;
};
struct btf *btf_vmlinux;
@@ -581,6 +582,7 @@ static char slot_type_char[] = {
[STACK_SPILL] = 'r',
[STACK_MISC] = 'm',
[STACK_ZERO] = '0',
+ [STACK_DYNPTR] = 'd',
};
static void print_liveness(struct bpf_verifier_env *env,
@@ -596,6 +598,25 @@ static void print_liveness(struct bpf_verifier_env *env,
verbose(env, "D");
}
+static int get_spi(s32 off)
+{
+ return (-off - 1) / BPF_REG_SIZE;
+}
+
+static bool is_spi_bounds_valid(struct bpf_func_state *state, int spi, int nr_slots)
+{
+ int allocated_slots = state->allocated_stack / BPF_REG_SIZE;
+
+ /* We need to check that slots between [spi - nr_slots + 1, spi] are
+ * within [0, allocated_stack).
+ *
+ * Please note that the spi grows downwards. For example, a dynptr
+ * takes the size of two stack slots; the first slot will be at
+ * spi and the second slot will be at spi - 1.
+ */
+ return spi - nr_slots + 1 >= 0 && spi < allocated_slots;
+}
+
static struct bpf_func_state *func(struct bpf_verifier_env *env,
const struct bpf_reg_state *reg)
{
@@ -647,6 +668,108 @@ static void mark_verifier_state_scratched(struct bpf_verifier_env *env)
env->scratched_stack_slots = ~0ULL;
}
+static enum bpf_dynptr_type arg_to_dynptr_type(enum bpf_arg_type arg_type)
+{
+ switch (arg_type & DYNPTR_TYPE_FLAG_MASK) {
+ case DYNPTR_TYPE_LOCAL:
+ return BPF_DYNPTR_TYPE_LOCAL;
+ default:
+ return BPF_DYNPTR_TYPE_INVALID;
+ }
+}
+
+static int mark_stack_slots_dynptr(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
+ enum bpf_arg_type arg_type, int insn_idx)
+{
+ struct bpf_func_state *state = func(env, reg);
+ enum bpf_dynptr_type type;
+ int spi, i;
+
+ spi = get_spi(reg->off);
+
+ if (!is_spi_bounds_valid(state, spi, BPF_DYNPTR_NR_SLOTS))
+ return -EINVAL;
+
+ for (i = 0; i < BPF_REG_SIZE; i++) {
+ state->stack[spi].slot_type[i] = STACK_DYNPTR;
+ state->stack[spi - 1].slot_type[i] = STACK_DYNPTR;
+ }
+
+ type = arg_to_dynptr_type(arg_type);
+ if (type == BPF_DYNPTR_TYPE_INVALID)
+ return -EINVAL;
+
+ state->stack[spi].spilled_ptr.dynptr.first_slot = true;
+ state->stack[spi].spilled_ptr.dynptr.type = type;
+ state->stack[spi - 1].spilled_ptr.dynptr.type = type;
+
+ return 0;
+}
+
+static int unmark_stack_slots_dynptr(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
+{
+ struct bpf_func_state *state = func(env, reg);
+ int spi, i;
+
+ spi = get_spi(reg->off);
+
+ if (!is_spi_bounds_valid(state, spi, BPF_DYNPTR_NR_SLOTS))
+ return -EINVAL;
+
+ for (i = 0; i < BPF_REG_SIZE; i++) {
+ state->stack[spi].slot_type[i] = STACK_INVALID;
+ state->stack[spi - 1].slot_type[i] = STACK_INVALID;
+ }
+
+ state->stack[spi].spilled_ptr.dynptr.first_slot = false;
+ state->stack[spi].spilled_ptr.dynptr.type = 0;
+ state->stack[spi - 1].spilled_ptr.dynptr.type = 0;
+
+ return 0;
+}
+
+static bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
+{
+ struct bpf_func_state *state = func(env, reg);
+ int spi = get_spi(reg->off);
+ int i;
+
+ if (!is_spi_bounds_valid(state, spi, BPF_DYNPTR_NR_SLOTS))
+ return true;
+
+ for (i = 0; i < BPF_REG_SIZE; i++) {
+ if (state->stack[spi].slot_type[i] == STACK_DYNPTR ||
+ state->stack[spi - 1].slot_type[i] == STACK_DYNPTR)
+ return false;
+ }
+
+ return true;
+}
+
+static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
+ enum bpf_arg_type arg_type)
+{
+ struct bpf_func_state *state = func(env, reg);
+ int spi = get_spi(reg->off);
+ int i;
+
+ if (!is_spi_bounds_valid(state, spi, BPF_DYNPTR_NR_SLOTS) ||
+ !state->stack[spi].spilled_ptr.dynptr.first_slot)
+ return false;
+
+ for (i = 0; i < BPF_REG_SIZE; i++) {
+ if (state->stack[spi].slot_type[i] != STACK_DYNPTR ||
+ state->stack[spi - 1].slot_type[i] != STACK_DYNPTR)
+ return false;
+ }
+
+ /* ARG_PTR_TO_DYNPTR takes any type of dynptr */
+ if (arg_type == ARG_PTR_TO_DYNPTR)
+ return true;
+
+ return state->stack[spi].spilled_ptr.dynptr.type == arg_to_dynptr_type(arg_type);
+}
+
/* The reg state of a pointer or a bounded scalar was saved when
* it was spilled to the stack.
*/
@@ -5400,6 +5523,11 @@ static bool arg_type_is_release(enum bpf_arg_type type)
return type & OBJ_RELEASE;
}
+static bool arg_type_is_dynptr(enum bpf_arg_type type)
+{
+ return base_type(type) == ARG_PTR_TO_DYNPTR;
+}
+
static int int_ptr_type_to_size(enum bpf_arg_type type)
{
if (type == ARG_PTR_TO_INT)
@@ -5539,6 +5667,7 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
[ARG_PTR_TO_CONST_STR] = &const_str_ptr_types,
[ARG_PTR_TO_TIMER] = &timer_types,
[ARG_PTR_TO_KPTR] = &kptr_types,
+ [ARG_PTR_TO_DYNPTR] = &stack_ptr_types,
};
static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
@@ -5628,8 +5757,13 @@ int check_func_arg_reg_off(struct bpf_verifier_env *env,
bool fixed_off_ok = false;
switch ((u32)type) {
- case SCALAR_VALUE:
/* Pointer types where reg offset is explicitly allowed: */
+ case PTR_TO_STACK:
+ if (arg_type_is_dynptr(arg_type) && reg->off % BPF_REG_SIZE) {
+ verbose(env, "cannot pass in dynptr at an offset\n");
+ return -EINVAL;
+ }
+ fallthrough;
case PTR_TO_PACKET:
case PTR_TO_PACKET_META:
case PTR_TO_MAP_KEY:
@@ -5639,7 +5773,7 @@ int check_func_arg_reg_off(struct bpf_verifier_env *env,
case PTR_TO_MEM | MEM_ALLOC:
case PTR_TO_BUF:
case PTR_TO_BUF | MEM_RDONLY:
- case PTR_TO_STACK:
+ case SCALAR_VALUE:
/* Some of the argument types nevertheless require a
* zero register offset.
*/
@@ -5837,6 +5971,36 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
bool zero_size_allowed = (arg_type == ARG_CONST_SIZE_OR_ZERO);
err = check_mem_size_reg(env, reg, regno, zero_size_allowed, meta);
+ } else if (arg_type_is_dynptr(arg_type)) {
+ if (arg_type & MEM_UNINIT) {
+ if (!is_dynptr_reg_valid_uninit(env, reg)) {
+ verbose(env, "Dynptr has to be an uninitialized dynptr\n");
+ return -EINVAL;
+ }
+
+ /* We only support one dynptr being uninitialized at the moment,
+ * which is sufficient for the helper functions we have right now.
+ */
+ if (meta->uninit_dynptr_regno) {
+ verbose(env, "verifier internal error: multiple uninitialized dynptr args\n");
+ return -EFAULT;
+ }
+
+ meta->uninit_dynptr_regno = regno;
+ } else if (!is_dynptr_reg_valid_init(env, reg, arg_type)) {
+ const char *err_extra = "";
+
+ switch (arg_type & DYNPTR_TYPE_FLAG_MASK) {
+ case DYNPTR_TYPE_LOCAL:
+ err_extra = "local ";
+ break;
+ default:
+ break;
+ }
+ verbose(env, "Expected an initialized %sdynptr as arg #%d\n",
+ err_extra, arg + 1);
+ return -EINVAL;
+ }
} else if (arg_type_is_alloc_size(arg_type)) {
if (!tnum_is_const(reg->var_off)) {
verbose(env, "R%d is not a known constant'\n",
@@ -6970,9 +7134,27 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
regs = cur_regs(env);
+ if (meta.uninit_dynptr_regno) {
+ /* we write BPF_DW bits (8 bytes) at a time */
+ for (i = 0; i < BPF_DYNPTR_SIZE; i += 8) {
+ err = check_mem_access(env, insn_idx, meta.uninit_dynptr_regno,
+ i, BPF_DW, BPF_WRITE, -1, false);
+ if (err)
+ return err;
+ }
+
+ err = mark_stack_slots_dynptr(env, ®s[meta.uninit_dynptr_regno],
+ fn->arg_type[meta.uninit_dynptr_regno - BPF_REG_1],
+ insn_idx);
+ if (err)
+ return err;
+ }
+
if (meta.release_regno) {
err = -EINVAL;
- if (meta.ref_obj_id)
+ if (arg_type_is_dynptr(fn->arg_type[meta.release_regno - BPF_REG_1]))
+ err = unmark_stack_slots_dynptr(env, ®s[meta.release_regno]);
+ else if (meta.ref_obj_id)
err = release_reference(env, meta.ref_obj_id);
/* meta.ref_obj_id can only be 0 if register that is meant to be
* released is NULL, which must be > R0.
diff --git a/scripts/bpf_doc.py b/scripts/bpf_doc.py
index d5452f7eb996..855b937e7585 100755
--- a/scripts/bpf_doc.py
+++ b/scripts/bpf_doc.py
@@ -634,6 +634,7 @@ class PrinterHelpers(Printer):
'struct file',
'struct bpf_timer',
'struct mptcp_sock',
+ 'struct bpf_dynptr',
]
known_types = {
'...',
@@ -684,6 +685,7 @@ class PrinterHelpers(Printer):
'struct file',
'struct bpf_timer',
'struct mptcp_sock',
+ 'struct bpf_dynptr',
}
mapped_types = {
'u8': '__u8',
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 56688bee20d9..610944cb3389 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6528,6 +6528,11 @@ struct bpf_timer {
__u64 :64;
} __attribute__((aligned(8)));
+struct bpf_dynptr {
+ __u64 :64;
+ __u64 :64;
+} __attribute__((aligned(8)));
+
struct bpf_sysctl {
__u32 write; /* Sysctl is being read (= 0) or written (= 1).
* Allows 1,2,4-byte read, but no write.
--
2.30.2
