[PATCH bpf] bpf: Fix a bpf_jit_dump issue for x86_64 with sysctl bpf_jit_enable.

From: Yonghong Song <yhs@fb.com>
To: <bpf@vger.kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>, <kernel-team@fb.com>,
	Martin KaFai Lau <martin.lau@kernel.org>
Subject: [PATCH bpf] bpf: Fix a bpf_jit_dump issue for x86_64 with sysctl bpf_jit_enable.
Date: Thu, 8 Jun 2023 17:54:39 -0700	[thread overview]
Message-ID: <20230609005439.3173569-1-yhs@fb.com> (raw)

The sysctl net/core/bpf_jit_enable does not work now due to Commit
1022a5498f6f ("bpf, x86_64: Use bpf_jit_binary_pack_alloc").
The commit saved the jitted insns into 'rw_image' instead of 'image'
which caused bpf_jit_dump not dumping proper content.

With 'echo 2 > /proc/sys/net/core/bpf_jit_enable', run
'./test_progs -t fentry_test'. Without this patch, one of jitted
image for one particular prog is:
  flen=17 proglen=92 pass=4 image=0000000014c64883 from=test_progs pid=1807
  00000000: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
  00000010: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
  00000020: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
  00000030: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
  00000040: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
  00000050: cc cc cc cc cc cc cc cc cc cc cc cc

With this patch, the jitte image for the same prog is:
  flen=17 proglen=92 pass=4 image=00000000b90254b7 from=test_progs pid=1809
  00000000: f3 0f 1e fa 0f 1f 44 00 00 66 90 55 48 89 e5 f3
  00000010: 0f 1e fa 31 f6 48 8b 57 00 48 83 fa 07 75 2b 48
  00000020: 8b 57 10 83 fa 09 75 22 48 8b 57 08 48 81 e2 ff
  00000030: 00 00 00 48 83 fa 08 75 11 48 8b 7f 18 be 01 00
  00000040: 00 00 48 83 ff 0a 74 02 31 f6 48 bf 18 d0 14 00
  00000050: 00 c9 ff ff 48 89 77 00 31 c0 c9 c3

Fixes: 1022a5498f6f ("bpf, x86_64: Use bpf_jit_binary_pack_alloc")
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 arch/x86/net/bpf_jit_comp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 1056bbf55b17..438adb695daa 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -2570,7 +2570,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 	}
 
 	if (bpf_jit_enable > 1)
-		bpf_jit_dump(prog->len, proglen, pass + 1, image);
+		bpf_jit_dump(prog->len, proglen, pass + 1, rw_image);
 
 	if (image) {
 		if (!prog->is_func || extra_pass) {
-- 
2.34.1

