Re: [PATCH] bpf/verifier: fix control flow issues in __reg64_bound_u32()

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On 7/28/22 10:49 PM, Zeng Jingxiang wrote:
From: Zeng Jingxiang <linuszeng@xxxxxxxxxxx>

This greater-than-or-equal-to-zero comparison of an unsigned value
is always true. "a >= U32_MIN".
1632	return a >= U32_MIN && a <= U32_MAX;

Fixes: b9979db83401 ("bpf: Fix propagation of bounds from 64-bit min/max into 32-bit and var_off.")
Signed-off-by: Zeng Jingxiang <linuszeng@xxxxxxxxxxx>
---
  kernel/bpf/verifier.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0efbac0fd126..dd67108fb1d7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1629,7 +1629,7 @@ static bool __reg64_bound_s32(s64 a)
static bool __reg64_bound_u32(u64 a)
  {
-	return a >= U32_MIN && a <= U32_MAX;
+	return a <= U32_MAX;
  }

I cannot find the related link. But IIRC, Alexei commented that
the code is written this way to express the intention (within
32bit bounds) so this patch is unnecessary...

static void __reg_combine_64_into_32(struct bpf_reg_state *reg)



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