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From: Kees Cook <keescook@chromium.org>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jann Horn <jannh@google.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	bpf <bpf@vger.kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>
Subject: Re: CONFIG_DEBUG_INFO_BTF and CONFIG_GCC_PLUGIN_RANDSTRUCT
Date: Tue, 31 Mar 2020 11:12:29 -0700	[thread overview]
Message-ID: <202003311110.2B08091E@keescook> (raw)
In-Reply-To: <c332da87-a770-8cf9-c252-5fb64c06c17e@iogearbox.net>

On Tue, Mar 31, 2020 at 12:41:04AM +0200, Daniel Borkmann wrote:
> On 3/30/20 7:20 PM, Kees Cook wrote:
> > On Mon, Mar 30, 2020 at 06:17:32PM +0200, Jann Horn wrote:
> > > On Mon, Mar 30, 2020 at 5:59 PM Alexei Starovoitov
> > > <alexei.starovoitov@gmail.com> wrote:
> > > > On Mon, Mar 30, 2020 at 8:14 AM Jann Horn <jannh@google.com> wrote:
> > > > > 
> > > > > I noticed that CONFIG_DEBUG_INFO_BTF seems to partly defeat the point
> > > > > of CONFIG_GCC_PLUGIN_RANDSTRUCT.
> > > > 
> > > > Is it a theoretical stmt or you have data?
> > > > I think it's the other way around.
> > > > gcc-plugin breaks dwarf and breaks btf.
> > > > But I only looked at gcc patches without applying them.
> > > 
> > > Ah, interesting - I haven't actually tested it, I just assumed
> > > (perhaps incorrectly) that the GCC plugin would deal with DWARF info
> > > properly.
> > 
> > Yeah, GCC appears to create DWARF before the plugin does the
> > randomization[1], so it's not an exposure, but yes, struct randomization
> > is pretty completely incompatible with a bunch of things in the kernel
> > (by design). I'm happy to add negative "depends" in the Kconfig if it
> > helps clarify anything.
> 
> Is this expected to get fixed at some point wrt DWARF? Perhaps would make

No, gcc closed the issue as "won't fix".

> sense then to add a negative "depends" for both DWARF and BTF if the option
> GCC_PLUGIN_RANDSTRUCT is set given both would be incompatible/broken.

I hadn't just to keep wider randconfig build test coverage. That said, I
could make it be: depends COMPILE_TEST || !DWARF ...

I can certainly do that.

-Kees

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84052

-- 
Kees Cook

  reply	other threads:[~2020-03-31 18:12 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-30 15:12 Jann Horn
2020-03-30 15:59 ` Alexei Starovoitov
2020-03-30 16:17   ` Jann Horn
2020-03-30 17:20     ` Kees Cook
2020-03-30 22:41       ` Daniel Borkmann
2020-03-31 18:12         ` Kees Cook [this message]
2020-03-31 19:50           ` Andrii Nakryiko
2020-03-31 19:58             ` Kees Cook
2020-03-31 20:23               ` Andrii Nakryiko
2020-03-31 21:24                 ` Slava Bacherikov
2020-04-01  7:32                   ` Kees Cook

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