diff options
| author | Andrii Nakryiko <andrii@kernel.org> | 2023-12-05 10:42:44 -0800 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2023-12-05 13:40:21 -0800 |
| commit | e322f0bcb8d371f4606eaf141c7f967e1a79bcb7 (patch) | |
| tree | 465b4dead3816fce4a5b27dafd7f566fb5b75da4 /kernel/bpf/verifier.c | |
| parent | b33ceb6a3d2ee07fdd836373383a6d4783581324 (diff) | |
bpf: preserve constant zero when doing partial register restore
Similar to special handling of STACK_ZERO, when reading 1/2/4 bytes from
stack from slot that has register spilled into it and that register has
a constant value zero, preserve that zero and mark spilled register as
precise for that. This makes spilled const zero register and STACK_ZERO
cases equivalent in their behavior.
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231205184248.1502704-7-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf/verifier.c')
| -rw-r--r-- | kernel/bpf/verifier.c | 25 |
1 files changed, 21 insertions, 4 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 93de39a6e36e..1ebe76c98451 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -4767,22 +4767,39 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env, copy_register_state(&state->regs[dst_regno], reg); state->regs[dst_regno].subreg_def = subreg_def; } else { + int spill_cnt = 0, zero_cnt = 0; + for (i = 0; i < size; i++) { type = stype[(slot - i) % BPF_REG_SIZE]; - if (type == STACK_SPILL) + if (type == STACK_SPILL) { + spill_cnt++; continue; + } if (type == STACK_MISC) continue; - if (type == STACK_ZERO) + if (type == STACK_ZERO) { + zero_cnt++; continue; + } if (type == STACK_INVALID && env->allow_uninit_stack) continue; verbose(env, "invalid read from stack off %d+%d size %d\n", off, i, size); return -EACCES; } - mark_reg_unknown(env, state->regs, dst_regno); - insn_flags = 0; /* not restoring original register state */ + + if (spill_cnt == size && + tnum_is_const(reg->var_off) && reg->var_off.value == 0) { + __mark_reg_const_zero(&state->regs[dst_regno]); + /* this IS register fill, so keep insn_flags */ + } else if (zero_cnt == size) { + /* similarly to mark_reg_stack_read(), preserve zeroes */ + __mark_reg_const_zero(&state->regs[dst_regno]); + insn_flags = 0; /* not restoring original register state */ + } else { + mark_reg_unknown(env, state->regs, dst_regno); + insn_flags = 0; /* not restoring original register state */ + } } state->regs[dst_regno].live |= REG_LIVE_WRITTEN; } else if (dst_regno >= 0) { |