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From: Daniel Borkmann <daniel@iogearbox.net>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>, davem@davemloft.net
Cc: josef@toxicpanda.com, bpoirier@suse.com,
	akpm@linux-foundation.org, hannes@cmpxchg.org,
	netdev@vger.kernel.org, bpf@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH v3 bpf-next 1/5] mm/error_inject: Fix allow_error_inject function signatures.
Date: Fri, 28 Aug 2020 22:27:25 +0200	[thread overview]
Message-ID: <d6eae293-5427-d5e4-73aa-4df7a493bb89@iogearbox.net> (raw)
In-Reply-To: <20200827220114.69225-2-alexei.starovoitov@gmail.com>

On 8/28/20 12:01 AM, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@kernel.org>
> 
> 'static' and 'static noinline' function attributes make no guarantees that
> gcc/clang won't optimize them. The compiler may decide to inline 'static'
> function and in such case ALLOW_ERROR_INJECT becomes meaningless. The compiler
> could have inlined __add_to_page_cache_locked() in one callsite and didn't
> inline in another. In such case injecting errors into it would cause
> unpredictable behavior. It's worse with 'static noinline' which won't be
> inlined, but it still can be optimized. Like the compiler may decide to remove
> one argument or constant propagate the value depending on the callsite.
> 
> To avoid such issues make sure that these functions are global noinline.

Back in the days when adding 6bf37e5aa90f ("crypto: crypto_memneq - add equality
testing of memory regions w/o timing leaks") we added noinline, but also an
explicit EXPORT_SYMBOL() to prevent this from being optimized away; I wonder
whether ALLOW_ERROR_INJECT() should have something implicit here too to prevent
from optimization .. otoh we probably don't want to expose every ALLOW_ERROR_INJECT()
function also to modules generically...

Thanks,
Daniel

  parent reply	other threads:[~2020-08-28 20:27 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-27 22:01 [PATCH v3 bpf-next 0/5] bpf: Introduce minimal support for sleepable progs Alexei Starovoitov
2020-08-27 22:01 ` [PATCH v3 bpf-next 1/5] mm/error_inject: Fix allow_error_inject function signatures Alexei Starovoitov
2020-08-27 23:58   ` Josef Bacik
2020-08-28 20:27   ` Daniel Borkmann [this message]
2020-08-29 22:47     ` Alexei Starovoitov
2020-08-27 22:01 ` [PATCH v3 bpf-next 2/5] bpf: Introduce sleepable BPF programs Alexei Starovoitov
2020-08-27 22:28   ` KP Singh
2020-08-28  1:01   ` Josef Bacik
2020-08-31 14:51   ` Björn Töpel
2020-08-31 16:26     ` Alexei Starovoitov
2020-08-27 22:01 ` [PATCH v3 bpf-next 3/5] bpf: Add bpf_copy_from_user() helper Alexei Starovoitov
2020-08-27 22:29   ` KP Singh
2020-08-27 22:01 ` [PATCH v3 bpf-next 4/5] libbpf: support sleepable progs Alexei Starovoitov
2020-08-27 22:01 ` [PATCH v3 bpf-next 5/5] selftests/bpf: Add sleepable tests Alexei Starovoitov
2020-08-29 22:13   ` Yonghong Song
2020-08-29 22:38     ` Alexei Starovoitov
2020-08-30  0:22       ` Yonghong Song
2020-08-31 16:56         ` Alexei Starovoitov
2020-08-28 20:10 ` [PATCH v3 bpf-next 0/5] bpf: Introduce minimal support for sleepable progs Daniel Borkmann

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