From 32f96222c6867c7d72de7f5f676619748a166117 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Thu, 31 Oct 2019 20:34:44 -0700
Subject: [PATCH] powerpc/bpf: Fix tail call implementation
References: bsc#1157698
Patch-mainline: v5.4-rc7
Git-commit: 7de086909365cd60a5619a45af3f4152516fd75c
We have seen many crashes on powerpc hosts while loading bpf programs.
The problem here is that bpf_int_jit_compile() does a first pass
to compute the program length.
Then it allocates memory to store the generated program and
calls bpf_jit_build_body() a second time (and a third time
later)
What I have observed is that the second bpf_jit_build_body()
could end up using few more words than expected.
If bpf_jit_binary_alloc() put the space for the program
at the end of the allocated page, we then write on
a non mapped memory.
It appears that bpf_jit_emit_tail_call() calls
bpf_jit_emit_common_epilogue() while ctx->seen might not
be stable.
Only after the second pass we can be sure ctx->seen wont be changed.
Trying to avoid a second pass seems quite complex and probably
not worth it.
Fixes: ce0761419faef ("powerpc/bpf: Implement support for tail calls")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
Cc: Sandipan Das <sandipan@linux.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20191101033444.143741-1-edumazet@google.com
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
arch/powerpc/net/bpf_jit_comp64.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index a20d80eec91d..3fc213d197bc 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -1024,6 +1024,19 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
goto out;
}
+ /*
+ * If we have seen a tail call, we need a second pass.
+ * This is because bpf_jit_emit_common_epilogue() is called
+ * from bpf_jit_emit_tail_call() with a not yet stable ctx->seen.
+ */
+ if (cgctx.seen & SEEN_TAILCALL) {
+ cgctx.idx = 0;
+ if (bpf_jit_build_body(fp, 0, &cgctx, addrs)) {
+ fp = org_fp;
+ goto out;
+ }
+ }
+
/*
* Pretend to build prologue, given the features we've seen. This will
* update ctgtx.idx as it pretends to output instructions, then we can
--
2.23.0