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| author | Alexei Starovoitov <ast@kernel.org> | 2020-12-08 19:01:51 +0100 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2020-12-10 13:02:53 -0800 |
| commit | b02709587ea3d699a608568ee8157d8db4fd8cae (patch) | |
| tree | fa020a03b80b74b93d1751f5e7b2108f4eea074e /kernel/bpf/verifier.c | |
| parent | 4e083fdfa39db29bbc7725e229e701867d0da183 (diff) | |
| download | lwn-b02709587ea3d699a608568ee8157d8db4fd8cae.tar.gz lwn-b02709587ea3d699a608568ee8157d8db4fd8cae.zip | |
bpf: Fix propagation of 32-bit signed bounds from 64-bit bounds.
The 64-bit signed bounds should not affect 32-bit signed bounds unless the
verifier knows that upper 32-bits are either all 1s or all 0s. For example the
register with smin_value==1 doesn't mean that s32_min_value is also equal to 1,
since smax_value could be larger than 32-bit subregister can hold.
The verifier refines the smax/s32_max return value from certain helpers in
do_refine_retval_range(). Teach the verifier to recognize that smin/s32_min
value is also bounded. When both smin and smax bounds fit into 32-bit
subregister the verifier can propagate those bounds.
Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking")
Reported-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf/verifier.c')
| -rw-r--r-- | kernel/bpf/verifier.c | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 1388bf733071..53fe6ef6d931 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1298,9 +1298,7 @@ static void __reg_combine_32_into_64(struct bpf_reg_state *reg) static bool __reg64_bound_s32(s64 a) { - if (a > S32_MIN && a < S32_MAX) - return true; - return false; + return a > S32_MIN && a < S32_MAX; } static bool __reg64_bound_u32(u64 a) @@ -1314,10 +1312,10 @@ static void __reg_combine_64_into_32(struct bpf_reg_state *reg) { __mark_reg32_unbounded(reg); - if (__reg64_bound_s32(reg->smin_value)) + if (__reg64_bound_s32(reg->smin_value) && __reg64_bound_s32(reg->smax_value)) { reg->s32_min_value = (s32)reg->smin_value; - if (__reg64_bound_s32(reg->smax_value)) reg->s32_max_value = (s32)reg->smax_value; + } if (__reg64_bound_u32(reg->umin_value)) reg->u32_min_value = (u32)reg->umin_value; if (__reg64_bound_u32(reg->umax_value)) @@ -4895,6 +4893,8 @@ static void do_refine_retval_range(struct bpf_reg_state *regs, int ret_type, ret_reg->smax_value = meta->msize_max_value; ret_reg->s32_max_value = meta->msize_max_value; + ret_reg->smin_value = -MAX_ERRNO; + ret_reg->s32_min_value = -MAX_ERRNO; __reg_deduce_bounds(ret_reg); __reg_bound_offset(ret_reg); __update_reg_bounds(ret_reg); |