netdev - [PATCH bpf-next 1/4] bpf, x86: Fall back to interpreter mode when extra pass fails

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Date:   Wed, 9 Mar 2022 20:33:18 +0800
From:   Hou Tao <houtao1@...wei.com>
To:     Alexei Starovoitov <ast@...nel.org>
CC:     Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        KP Singh <kpsingh@...nel.org>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>, <houtao1@...wei.com>
Subject: [PATCH bpf-next 1/4] bpf, x86: Fall back to interpreter mode when extra pass fails

Extra pass for subprog jit may fail (e.g. due to bpf_jit_harden race),
but bpf_func is not cleared for the subprog and jit_subprogs will
succeed. The running of the bpf program may lead to oops because the
memory for the jited subprog image has already been freed.

So fall back to interpreter mode by clearing bpf_func/jited/jited_len
when extra pass fails.

Signed-off-by: Hou Tao <houtao1@...wei.com>
---
 arch/x86/net/bpf_jit_comp.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index e6ff8f4f9ea4..ec3f00be2ac5 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -2335,7 +2335,13 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 						   sizeof(rw_header->size));
 				bpf_jit_binary_pack_free(header, rw_header);
 			}
+			/* Fall back to interpreter mode */
 			prog = orig_prog;
+			if (extra_pass) {
+				prog->bpf_func = NULL;
+				prog->jited = 0;
+				prog->jited_len = 0;
+			}
 			goto out_addrs;
 		}
 		if (image) {
@@ -2384,8 +2390,9 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 			 * Both cases are serious bugs and justify WARN_ON.
 			 */
 			if (WARN_ON(bpf_jit_binary_pack_finalize(prog, header, rw_header))) {
-				prog = orig_prog;
-				goto out_addrs;
+				/* header has been freed */
+				header = NULL;
+				goto out_image;
 			}
 
 			bpf_tail_call_direct_fixup(prog);
-- 
2.29.2