https://github.com/torvalds/linux
Revision 77ce220c0549dcc3db8226c61c60e83fc59dfafc authored by Jean-Philippe Brucker on 08 December 2020, 18:01:53 UTC, committed by Alexei Starovoitov on 10 December 2020, 21:11:30 UTC
The test fails because of a recent fix to the verifier, even though this
program is valid. In details what happens is:
7: (61) r1 = *(u32 *)(r0 +0)
Load a 32-bit value, with signed bounds [S32_MIN, S32_MAX]. The bounds
of the 64-bit value are [0, U32_MAX]...
8: (65) if r1 s> 0xffffffff goto pc+1
... therefore this is always true (the operand is sign-extended).
10: (b4) w2 = 11
11: (6d) if r2 s> r1 goto pc+1
When true, the 64-bit bounds become [0, 10]. The 32-bit bounds are still
[S32_MIN, 10].
13: (64) w1 <<= 2
Because this is a 32-bit operation, the verifier propagates the new
32-bit bounds to the 64-bit ones, and the knowledge gained from insn 11
is lost.
14: (0f) r0 += r1
15: (7a) *(u64 *)(r0 +0) = 4
Then the verifier considers r0 unbounded here, rejecting the test. To
make the test work, change insn 8 to check the sign of the 32-bit value.
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
1 parent 511a76b
Tip revision: 77ce220c0549dcc3db8226c61c60e83fc59dfafc authored by Jean-Philippe Brucker on 08 December 2020, 18:01:53 UTC
selftests/bpf: Fix array access with signed variable test
selftests/bpf: Fix array access with signed variable test
Tip revision: 77ce220
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