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author | Eric Dumazet <edumazet@google.com> | 2019-11-01 04:34:44 +0100 |
---|---|---|
committer | Daniel Borkmann <daniel@iogearbox.net> | 2019-11-02 00:32:26 +0100 |
commit | 7de086909365cd60a5619a45af3f4152516fd75c (patch) | |
tree | 877ccc41536b3d95a334706daf59dcce52ef7d9d /arch | |
parent | bpf: Change size to u64 for bpf_map_{area_alloc, charge_init}() (diff) | |
download | linux-7de086909365cd60a5619a45af3f4152516fd75c.tar.xz linux-7de086909365cd60a5619a45af3f4152516fd75c.zip |
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: 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
Diffstat (limited to 'arch')
-rw-r--r-- | arch/powerpc/net/bpf_jit_comp64.c | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c index 02a59946a78a..be3517ef0574 100644 --- a/arch/powerpc/net/bpf_jit_comp64.c +++ b/arch/powerpc/net/bpf_jit_comp64.c @@ -1142,6 +1142,19 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) } /* + * 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 * calculate total size from idx. |