From: David Miller <davem@davemloft.net>
To: edumazet@google.com
Cc: ast@kernel.org, daniel@iogearbox.net, netdev@vger.kernel.org,
eric.dumazet@gmail.com, bpf@vger.kernel.org,
naveen.n.rao@linux.ibm.com, sandipan@linux.ibm.com,
benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
kafai@fb.com, songliubraving@fb.com, yhs@fb.com
Subject: Re: [PATCH net] powerpc/bpf: fix tail call implementation
Date: Thu, 31 Oct 2019 21:39:31 -0700 (PDT) [thread overview]
Message-ID: <20191031.213931.1743556905343073518.davem@davemloft.net> (raw)
In-Reply-To: <20191101033444.143741-1-edumazet@google.com>
From: Eric Dumazet <edumazet@google.com>
Date: Thu, 31 Oct 2019 20:34:44 -0700
> 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>
I am anticipating this will go via the bpf tree.
next prev parent reply other threads:[~2019-11-01 4:39 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-01 3:34 [PATCH net] powerpc/bpf: fix tail call implementation Eric Dumazet
2019-11-01 4:39 ` David Miller [this message]
2019-11-02 0:05 ` Daniel Borkmann
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