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bpf: Fix propagation of 32-bit signed bounds from 64-bit bounds.

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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: 3f50f132d8 ("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>
This commit is contained in:
Alexei Starovoitov 2020-12-08 19:01:51 +01:00
parent 4e083fdfa3
commit b02709587e
1 changed files with 5 additions and 5 deletions
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10
kernel/bpf/verifier.c
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@ -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);