This is a note to let you know that I've just added the patch titled
selftests/bpf: Fix pointer arithmetic in test_xdp_do_redirect
to the 6.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
selftests-bpf-fix-pointer-arithmetic-in-test_xdp_do_.patch
and it can be found in the queue-6.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit ec6cdf7bc485da54a891d4a1a685327a5674c362
Author: Michal Schmidt <mschmidt@xxxxxxxxxx>
Date: Mon May 6 16:50:22 2024 +0200
selftests/bpf: Fix pointer arithmetic in test_xdp_do_redirect
[ Upstream commit e549b39a0ab8880d7ae6c6495b00fc1cb8f36174 ]
Cast operation has a higher precedence than addition. The code here
wants to zero the 2nd half of the 64-bit metadata, but due to a pointer
arithmetic mistake, it writes the zero at offset 16 instead.
Just adding parentheses around "data + 4" would fix this, but I think
this will be slightly better readable with array syntax.
I was unable to test this with tools/testing/selftests/bpf/vmtest.sh,
because my glibc is newer than glibc in the provided VM image.
So I just checked the difference in the compiled code.
objdump -S tools/testing/selftests/bpf/xdp_do_redirect.test.o:
- *((__u32 *)data) = 0x42; /* metadata test value */
+ ((__u32 *)data)[0] = 0x42; /* metadata test value */
be7: 48 8d 85 30 fc ff ff lea -0x3d0(%rbp),%rax
bee: c7 00 42 00 00 00 movl $0x42,(%rax)
- *((__u32 *)data + 4) = 0;
+ ((__u32 *)data)[1] = 0;
bf4: 48 8d 85 30 fc ff ff lea -0x3d0(%rbp),%rax
- bfb: 48 83 c0 10 add $0x10,%rax
+ bfb: 48 83 c0 04 add $0x4,%rax
bff: c7 00 00 00 00 00 movl $0x0,(%rax)
Fixes: 5640b6d89434 ("selftests/bpf: fix "metadata marker" getting overwritten by the netstack")
Signed-off-by: Michal Schmidt <mschmidt@xxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Reviewed-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20240506145023.214248-1-mschmidt@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c b/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c
index 498d3bdaa4b0b..bad0ea167be70 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c
@@ -107,8 +107,8 @@ void test_xdp_do_redirect(void)
.attach_point = BPF_TC_INGRESS);
memcpy(&data[sizeof(__u64)], &pkt_udp, sizeof(pkt_udp));
- *((__u32 *)data) = 0x42; /* metadata test value */
- *((__u32 *)data + 4) = 0;
+ ((__u32 *)data)[0] = 0x42; /* metadata test value */
+ ((__u32 *)data)[1] = 0;
skel = test_xdp_do_redirect__open();
if (!ASSERT_OK_PTR(skel, "skel"))
