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Subject[PATCH 5.3 035/135] powerpc/bpf: Fix tail call implementation
From: Eric Dumazet <>

[ Upstream 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

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 <>
Signed-off-by: Daniel Borkmann <>
Cc: Naveen N. Rao <>
Cc: Sandipan Das <>
Cc: Benjamin Herrenschmidt <>
Cc: Paul Mackerras <>
Cc: Michael Ellerman <>
Cc: Martin KaFai Lau <>
Cc: Song Liu <>
Cc: Yonghong Song <>
Signed-off-by: Sasha Levin <>
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 02a59946a78af..be3517ef0574d 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -1141,6 +1141,19 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
goto out_addrs;

+ /*
+ * 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, false)) {
+ fp = org_fp;
+ goto out_addrs;
+ }
+ }
* Pretend to build prologue, given the features we've seen. This will
* update ctgtx.idx as it pretends to output instructions, then we can

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