From 3b9d9a893fed59551d2be775035b5094edc982fa Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 31 Oct 2019 20:34:44 -0700 Subject: [PATCH] powerpc/bpf: Fix tail call implementation 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: 43db670a33cd1 ("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 Link: https://lore.kernel.org/bpf/20191101033444.143741-1-edumazet@google.com --- 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 -- 2.39.5