From: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
[ Upstream commit 77ce220c0549dcc3db8226c61c60e83fc59dfafc ]
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@xxxxxxxxxx>
Acked-by: John Fastabend <john.fastabend@xxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
tools/testing/selftests/bpf/verifier/array_access.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/testing/selftests/bpf/verifier/array_access.c b/tools/testing/selftests/bpf/verifier/array_access.c
index 1c4b1939f5a8d..bed53b561e044 100644
--- a/tools/testing/selftests/bpf/verifier/array_access.c
+++ b/tools/testing/selftests/bpf/verifier/array_access.c
@@ -68,7 +68,7 @@
BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 9),
BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_0, 0),
- BPF_JMP_IMM(BPF_JSGT, BPF_REG_1, 0xffffffff, 1),
+ BPF_JMP32_IMM(BPF_JSGT, BPF_REG_1, 0xffffffff, 1),
BPF_MOV32_IMM(BPF_REG_1, 0),
BPF_MOV32_IMM(BPF_REG_2, MAX_ENTRIES),
BPF_JMP_REG(BPF_JSGT, BPF_REG_2, BPF_REG_1, 1),
--
2.27.0
