From: Eric Dumazet edumazet@google.com
[ 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 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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 279a51bf94d05..7e3ab477f67fe 100644 --- a/arch/powerpc/net/bpf_jit_comp64.c +++ b/arch/powerpc/net/bpf_jit_comp64.c @@ -949,6 +949,19 @@ 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