On Wed, 2023-07-12 at 23:07 -0700, Yonghong Song wrote:
> Add interpreter/jit support for new sign-extension load insns
> which adds a new mode (BPF_MEMSX).
> Also add verifier support to recognize these insns and to
> do proper verification with new insns. In verifier, besides
> to deduce proper bounds for the dst_reg, probed memory access
> is handled by remembering insn mode in insn->imm field so later
> on proper jit insns can be emitted.
>
> Signed-off-by: Yonghong Song <yhs@xxxxxx>
> ---
> arch/x86/net/bpf_jit_comp.c | 32 ++++++++-
> include/uapi/linux/bpf.h | 1 +
> kernel/bpf/core.c | 13 ++++
> kernel/bpf/verifier.c | 125 +++++++++++++++++++++++++++------
> tools/include/uapi/linux/bpf.h | 1 +
> 5 files changed, 151 insertions(+), 21 deletions(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 438adb695daa..addeea95f397 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -779,6 +779,29 @@ static void emit_ldx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
> *pprog = prog;
> }
>
> +/* LDX: dst_reg = *(s8*)(src_reg + off) */
> +static void emit_ldsx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
> +{
> + u8 *prog = *pprog;
> +
> + switch (size) {
> + case BPF_B:
> + /* Emit 'movsx rax, byte ptr [rax + off]' */
> + EMIT3(add_2mod(0x48, src_reg, dst_reg), 0x0F, 0xBE);
> + break;
> + case BPF_H:
> + /* Emit 'movsx rax, word ptr [rax + off]' */
> + EMIT3(add_2mod(0x48, src_reg, dst_reg), 0x0F, 0xBF);
> + break;
> + case BPF_W:
> + /* Emit 'movsx rax, dword ptr [rax+0x14]' */
> + EMIT2(add_2mod(0x48, src_reg, dst_reg), 0x63);
> + break;
> + }
> + emit_insn_suffix(&prog, src_reg, dst_reg, off);
> + *pprog = prog;
> +}
> +
> /* STX: *(u8*)(dst_reg + off) = src_reg */
> static void emit_stx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
> {
> @@ -1370,6 +1393,9 @@ st: if (is_imm8(insn->off))
> case BPF_LDX | BPF_PROBE_MEM | BPF_W:
> case BPF_LDX | BPF_MEM | BPF_DW:
> case BPF_LDX | BPF_PROBE_MEM | BPF_DW:
> + case BPF_LDX | BPF_MEMSX | BPF_B:
> + case BPF_LDX | BPF_MEMSX | BPF_H:
> + case BPF_LDX | BPF_MEMSX | BPF_W:
> insn_off = insn->off;
>
> if (BPF_MODE(insn->code) == BPF_PROBE_MEM) {
> @@ -1415,7 +1441,11 @@ st: if (is_imm8(insn->off))
> start_of_ldx = prog;
> end_of_jmp[-1] = start_of_ldx - end_of_jmp;
> }
> - emit_ldx(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn_off);
> + if ((BPF_MODE(insn->code) == BPF_PROBE_MEM && insn->imm == BPF_MEMSX) ||
> + BPF_MODE(insn->code) == BPF_MEMSX)
> + emit_ldsx(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn_off);
> + else
> + emit_ldx(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn_off);
> if (BPF_MODE(insn->code) == BPF_PROBE_MEM) {
> struct exception_table_entry *ex;
> u8 *_insn = image + proglen + (start_of_ldx - temp);
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 600d0caebbd8..c7196302d1eb 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -19,6 +19,7 @@
>
> /* ld/ldx fields */
> #define BPF_DW 0x18 /* double word (64-bit) */
> +#define BPF_MEMSX 0x80 /* load with sign extension */
> #define BPF_ATOMIC 0xc0 /* atomic memory ops - op type in immediate */
> #define BPF_XADD 0xc0 /* exclusive add - legacy name */
>
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index dc85240a0134..8a1cc658789e 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -1610,6 +1610,9 @@ EXPORT_SYMBOL_GPL(__bpf_call_base);
> INSN_3(LDX, MEM, H), \
> INSN_3(LDX, MEM, W), \
> INSN_3(LDX, MEM, DW), \
> + INSN_3(LDX, MEMSX, B), \
> + INSN_3(LDX, MEMSX, H), \
> + INSN_3(LDX, MEMSX, W), \
> /* Immediate based. */ \
> INSN_3(LD, IMM, DW)
>
> @@ -1942,6 +1945,16 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
> LDST(DW, u64)
> #undef LDST
>
> +#define LDS(SIZEOP, SIZE) \
> + LDX_MEMSX_##SIZEOP: \
> + DST = *(SIZE *)(unsigned long) (SRC + insn->off); \
> + CONT;
> +
> + LDS(B, s8)
> + LDS(H, s16)
> + LDS(W, s32)
> +#undef LDS
> +
> #define ATOMIC_ALU_OP(BOP, KOP) \
> case BOP: \
> if (BPF_SIZE(insn->code) == BPF_W) \
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 81a93eeac7a0..fbe4ca72d4c1 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -5795,6 +5795,77 @@ static void coerce_reg_to_size(struct bpf_reg_state *reg, int size)
> __reg_combine_64_into_32(reg);
> }
>
> +static void set_sext64_default_val(struct bpf_reg_state *reg, int size)
> +{
> + if (size == 1) {
> + reg->smin_value = reg->s32_min_value = S8_MIN;
> + reg->smax_value = reg->s32_max_value = S8_MAX;
> + } else if (size == 2) {
> + reg->smin_value = reg->s32_min_value = S16_MIN;
> + reg->smax_value = reg->s32_max_value = S16_MAX;
> + } else {
> + /* size == 4 */
> + reg->smin_value = reg->s32_min_value = S32_MIN;
> + reg->smax_value = reg->s32_max_value = S32_MAX;
> + }
> + reg->umin_value = reg->u32_min_value = 0;
> + reg->umax_value = U64_MAX;
> + reg->u32_max_value = U32_MAX;
> + reg->var_off = tnum_unknown;
> +}
> +
> +static void coerce_reg_to_size_sx(struct bpf_reg_state *reg, int size)
> +{
> + u64 top_smax_value, top_smin_value;
> + s64 init_s64_max, init_s64_min, s64_max, s64_min;
> + u64 num_bits = size * 8;
> +
> + top_smax_value = ((u64)reg->smax_value >> num_bits) << num_bits;
> + top_smin_value = ((u64)reg->smin_value >> num_bits) << num_bits;
> +
> + if (top_smax_value != top_smin_value)
> + goto out;
> +
> + /* find the s64_min and s64_min after sign extension */
> + if (size == 1) {
> + init_s64_max = (s8)reg->smax_value;
> + init_s64_min = (s8)reg->smin_value;
> + } else if (size == 2) {
> + init_s64_max = (s16)reg->smax_value;
> + init_s64_min = (s16)reg->smin_value;
> + } else {
> + /* size == 4 */
> + init_s64_max = (s32)reg->smax_value;
> + init_s64_min = (s32)reg->smin_value;
> + }
> +
> + s64_max = max(init_s64_max, init_s64_min);
> + s64_min = min(init_s64_max, init_s64_min);
> +
> + if (s64_max >= 0 && s64_min >= 0) {
> + reg->smin_value = reg->s32_min_value = s64_min;
> + reg->smax_value = reg->s32_max_value = s64_max;
> + reg->umin_value = reg->u32_min_value = s64_min;
> + reg->umax_value = reg->u32_max_value = s64_max;
> + reg->var_off = tnum_range(s64_min, s64_max);
> + return;
> + }
> +
> + if (s64_min < 0 && s64_max < 0) {
> + reg->smin_value = reg->s32_min_value = s64_min;
> + reg->smax_value = reg->s32_max_value = s64_max;
> + reg->umin_value = (u64)s64_max;
> + reg->umax_value = (u64)s64_min;
I think the last two assignments are not correct for the following example:
{
"testtesttest",
.insns = {
BPF_EMIT_CALL(BPF_FUNC_get_prandom_u32),
BPF_JMP_IMM(BPF_JLT, BPF_REG_0, 0xff80, 2),
BPF_JMP_IMM(BPF_JGT, BPF_REG_0, 0xffff, 1),
{
.code = BPF_ALU64 | BPF_MOV | BPF_X,
.dst_reg = BPF_REG_0,
.src_reg = BPF_REG_0,
.off = 8,
.imm = 0,
},
BPF_EXIT_INSN(),
},
.result = ACCEPT,
.retval = 0,
},
Here is execution log:
0: R1=ctx(off=0,imm=0) R10=fp0
0: (85) call bpf_get_prandom_u32#7 ; R0_w=Pscalar()
1: (a5) if r0 < 0xff80 goto pc+2 ; R0_w=Pscalar(umin=65408)
2: (25) if r0 > 0xffff goto pc+1 ; R0_w=Pscalar(umin=65408,umax=65535,var_off=(0xff80; 0x7f))
3: (bf) r0 = r0 ; R0_w=Pscalar
(smin=-128,smax=-1,
umin=18'446'744'073'709'551'615,
umax=18'446'744'073'709'551'488,
var_off=(0xffffffffffffff80; 0x7f),
u32_min=-1,u32_max=-128)
4: (95) exit
Note that umax < umin, which should not happen.
In this case the assignments in question are:
reg->umin_value = (u64)s64_max; // == -1 == 0xffffffffffffffff
reg->umax_value = (u64)s64_min; // == -128 == 0xffffffffffffff80
> + reg->u32_min_value = (u32)s64_max;
> + reg->u32_max_value = (u32)s64_min;
> + reg->var_off = tnum_range((u64)s64_max, (u64)s64_min);
> + return;
> + }
> +
> +out:
> + set_sext64_default_val(reg, size);
> +}
> +
> static bool bpf_map_is_rdonly(const struct bpf_map *map)
> {
> /* A map is considered read-only if the following condition are true:
> @@ -5815,7 +5886,8 @@ static bool bpf_map_is_rdonly(const struct bpf_map *map)
> !bpf_map_write_active(map);
> }
>
> -static int bpf_map_direct_read(struct bpf_map *map, int off, int size, u64 *val)
> +static int bpf_map_direct_read(struct bpf_map *map, int off, int size, u64 *val,
> + bool is_ldsx)
> {
> void *ptr;
> u64 addr;
> @@ -5828,13 +5900,13 @@ static int bpf_map_direct_read(struct bpf_map *map, int off, int size, u64 *val)
>
> switch (size) {
> case sizeof(u8):
> - *val = (u64)*(u8 *)ptr;
> + *val = is_ldsx ? (s64)*(s8 *)ptr : (u64)*(u8 *)ptr;
> break;
> case sizeof(u16):
> - *val = (u64)*(u16 *)ptr;
> + *val = is_ldsx ? (s64)*(s16 *)ptr : (u64)*(u16 *)ptr;
> break;
> case sizeof(u32):
> - *val = (u64)*(u32 *)ptr;
> + *val = is_ldsx ? (s64)*(s32 *)ptr : (u64)*(u32 *)ptr;
> break;
> case sizeof(u64):
> *val = *(u64 *)ptr;
> @@ -6248,7 +6320,7 @@ static int check_stack_access_within_bounds(
> */
> static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regno,
> int off, int bpf_size, enum bpf_access_type t,
> - int value_regno, bool strict_alignment_once)
> + int value_regno, bool strict_alignment_once, bool is_ldsx)
> {
> struct bpf_reg_state *regs = cur_regs(env);
> struct bpf_reg_state *reg = regs + regno;
> @@ -6309,7 +6381,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
> u64 val = 0;
>
> err = bpf_map_direct_read(map, map_off, size,
> - &val);
> + &val, is_ldsx);
> if (err)
> return err;
>
> @@ -6479,8 +6551,11 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
>
> if (!err && size < BPF_REG_SIZE && value_regno >= 0 && t == BPF_READ &&
> regs[value_regno].type == SCALAR_VALUE) {
> - /* b/h/w load zero-extends, mark upper bits as known 0 */
> - coerce_reg_to_size(®s[value_regno], size);
> + if (!is_ldsx)
> + /* b/h/w load zero-extends, mark upper bits as known 0 */
> + coerce_reg_to_size(®s[value_regno], size);
> + else
> + coerce_reg_to_size_sx(®s[value_regno], size);
> }
> return err;
> }
> @@ -6572,17 +6647,17 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
> * case to simulate the register fill.
> */
> err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
> - BPF_SIZE(insn->code), BPF_READ, -1, true);
> + BPF_SIZE(insn->code), BPF_READ, -1, true, false);
> if (!err && load_reg >= 0)
> err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
> BPF_SIZE(insn->code), BPF_READ, load_reg,
> - true);
> + true, false);
> if (err)
> return err;
>
> /* Check whether we can write into the same memory. */
> err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
> - BPF_SIZE(insn->code), BPF_WRITE, -1, true);
> + BPF_SIZE(insn->code), BPF_WRITE, -1, true, false);
> if (err)
> return err;
>
> @@ -6828,7 +6903,7 @@ static int check_helper_mem_access(struct bpf_verifier_env *env, int regno,
> return zero_size_allowed ? 0 : -EACCES;
>
> return check_mem_access(env, env->insn_idx, regno, offset, BPF_B,
> - atype, -1, false);
> + atype, -1, false, false);
> }
>
> fallthrough;
> @@ -7200,7 +7275,7 @@ static int process_dynptr_func(struct bpf_verifier_env *env, int regno, int insn
> /* 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, regno,
> - i, BPF_DW, BPF_WRITE, -1, false);
> + i, BPF_DW, BPF_WRITE, -1, false, false);
> if (err)
> return err;
> }
> @@ -7293,7 +7368,7 @@ static int process_iter_arg(struct bpf_verifier_env *env, int regno, int insn_id
>
> for (i = 0; i < nr_slots * 8; i += BPF_REG_SIZE) {
> err = check_mem_access(env, insn_idx, regno,
> - i, BPF_DW, BPF_WRITE, -1, false);
> + i, BPF_DW, BPF_WRITE, -1, false, false);
> if (err)
> return err;
> }
> @@ -9437,7 +9512,7 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
> */
> for (i = 0; i < meta.access_size; i++) {
> err = check_mem_access(env, insn_idx, meta.regno, i, BPF_B,
> - BPF_WRITE, -1, false);
> + BPF_WRITE, -1, false, false);
> if (err)
> return err;
> }
> @@ -16315,7 +16390,8 @@ static int do_check(struct bpf_verifier_env *env)
> */
> err = check_mem_access(env, env->insn_idx, insn->src_reg,
> insn->off, BPF_SIZE(insn->code),
> - BPF_READ, insn->dst_reg, false);
> + BPF_READ, insn->dst_reg, false,
> + BPF_MODE(insn->code) == BPF_MEMSX);
> if (err)
> return err;
>
> @@ -16352,7 +16428,7 @@ static int do_check(struct bpf_verifier_env *env)
> /* check that memory (dst_reg + off) is writeable */
> err = check_mem_access(env, env->insn_idx, insn->dst_reg,
> insn->off, BPF_SIZE(insn->code),
> - BPF_WRITE, insn->src_reg, false);
> + BPF_WRITE, insn->src_reg, false, false);
> if (err)
> return err;
>
> @@ -16377,7 +16453,7 @@ static int do_check(struct bpf_verifier_env *env)
> /* check that memory (dst_reg + off) is writeable */
> err = check_mem_access(env, env->insn_idx, insn->dst_reg,
> insn->off, BPF_SIZE(insn->code),
> - BPF_WRITE, -1, false);
> + BPF_WRITE, -1, false, false);
> if (err)
> return err;
>
> @@ -16805,7 +16881,8 @@ static int resolve_pseudo_ldimm64(struct bpf_verifier_env *env)
>
> for (i = 0; i < insn_cnt; i++, insn++) {
> if (BPF_CLASS(insn->code) == BPF_LDX &&
> - (BPF_MODE(insn->code) != BPF_MEM || insn->imm != 0)) {
> + ((BPF_MODE(insn->code) != BPF_MEM && BPF_MODE(insn->code) != BPF_MEMSX) ||
> + insn->imm != 0)) {
> verbose(env, "BPF_LDX uses reserved fields\n");
> return -EINVAL;
> }
> @@ -17503,7 +17580,10 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
> if (insn->code == (BPF_LDX | BPF_MEM | BPF_B) ||
> insn->code == (BPF_LDX | BPF_MEM | BPF_H) ||
> insn->code == (BPF_LDX | BPF_MEM | BPF_W) ||
> - insn->code == (BPF_LDX | BPF_MEM | BPF_DW)) {
> + insn->code == (BPF_LDX | BPF_MEM | BPF_DW) ||
> + insn->code == (BPF_LDX | BPF_MEMSX | BPF_B) ||
> + insn->code == (BPF_LDX | BPF_MEMSX | BPF_H) ||
> + insn->code == (BPF_LDX | BPF_MEMSX | BPF_W)) {
> type = BPF_READ;
> } else if (insn->code == (BPF_STX | BPF_MEM | BPF_B) ||
> insn->code == (BPF_STX | BPF_MEM | BPF_H) ||
> @@ -17562,6 +17642,11 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
> */
> case PTR_TO_BTF_ID | MEM_ALLOC | PTR_UNTRUSTED:
> if (type == BPF_READ) {
> + /* it is hard to differentiate that the
> + * BPF_PROBE_MEM is for BPF_MEM or BPF_MEMSX,
> + * let us use insn->imm to remember it.
> + */
> + insn->imm = BPF_MODE(insn->code);
> insn->code = BPF_LDX | BPF_PROBE_MEM |
> BPF_SIZE((insn)->code);
> env->prog->aux->num_exentries++;
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 600d0caebbd8..c7196302d1eb 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -19,6 +19,7 @@
>
> /* ld/ldx fields */
> #define BPF_DW 0x18 /* double word (64-bit) */
> +#define BPF_MEMSX 0x80 /* load with sign extension */
> #define BPF_ATOMIC 0xc0 /* atomic memory ops - op type in immediate */
> #define BPF_XADD 0xc0 /* exclusive add - legacy name */
>
