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bpf: remove redundant s{32,64} -> u{32,64} deduction logic

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Equivalent checks were recently added in more succinct and, arguably,
safer form in:
  - f188765f23a5 ("bpf: derive smin32/smax32 from umin32/umax32 bounds");
  - 2e74aef782d3 ("bpf: derive smin/smax from umin/max bounds").

The checks we are removing in this patch set do similar checks to detect
if entire u32/u64 range has signed bit set or not set, but does it with
two separate checks.

Further, we forcefully overwrite either smin or smax (and 32-bit equvalents)
without applying normal min/max intersection logic. It's not clear why
that would be correct in all cases and seems to work by accident. This
logic is also "gated" by previous signed -> unsigned derivation, which
returns early.

All this is quite confusing and seems error-prone, while we already have
at least equivalent checks happening earlier. So remove this duplicate
and error-prone logic to simplify things a bit.

Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231112010609.848406-6-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Andrii Nakryiko 2023-11-11 17:06:01 -08:00 committed by Alexei Starovoitov
parent 5f99f312bd
commit 3cf98cf594
1 changed files with 0 additions and 36 deletions
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36
kernel/bpf/verifier.c
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@ -2411,24 +2411,6 @@ static void __reg32_deduce_bounds(struct bpf_reg_state *reg)
min_t(u32, reg->s32_max_value, reg->u32_max_value);
return;
}
/* Learn sign from unsigned bounds. Signed bounds cross the sign
* boundary, so we must be careful.
*/
if ((s32)reg->u32_max_value >= 0) {
/* Positive. We can't learn anything from the smin, but smax
* is positive, hence safe.
*/
reg->s32_min_value = reg->u32_min_value;
reg->s32_max_value = reg->u32_max_value =
min_t(u32, reg->s32_max_value, reg->u32_max_value);
} else if ((s32)reg->u32_min_value < 0) {
/* Negative. We can't learn anything from the smax, but smin
* is negative, hence safe.
*/
reg->s32_min_value = reg->u32_min_value =
max_t(u32, reg->s32_min_value, reg->u32_min_value);
reg->s32_max_value = reg->u32_max_value;
}
}
static void __reg64_deduce_bounds(struct bpf_reg_state *reg)
@ -2516,24 +2498,6 @@ static void __reg64_deduce_bounds(struct bpf_reg_state *reg)
reg->umax_value);
return;
}
/* Learn sign from unsigned bounds. Signed bounds cross the sign
* boundary, so we must be careful.
*/
if ((s64)reg->umax_value >= 0) {
/* Positive. We can't learn anything from the smin, but smax
* is positive, hence safe.
*/
reg->smin_value = reg->umin_value;
reg->smax_value = reg->umax_value = min_t(u64, reg->smax_value,
reg->umax_value);
} else if ((s64)reg->umin_value < 0) {
/* Negative. We can't learn anything from the smax, but smin
* is negative, hence safe.
*/
reg->smin_value = reg->umin_value = max_t(u64, reg->smin_value,
reg->umin_value);
reg->smax_value = reg->umax_value;
}
}
static void __reg_deduce_mixed_bounds(struct bpf_reg_state *reg)