Re: [Regression v4.2 ?] 32-bit seccomp-BPF returned errno values wrong in VM?

From: Kees Cook <keescook@chromium.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	David Drysdale <drysdale@google.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Will Drewry <wad@chromium.org>, Ingo Molnar <mingo@kernel.org>,
	Alok Kataria <akataria@vmware.com>,
	Borislav Petkov <bp@alien8.de>,
	Alexei Starovoitov <ast@plumgrid.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Oleg Nesterov <oleg@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>, X86 ML <x86@kernel.org>
Subject: Re: [Regression v4.2 ?] 32-bit seccomp-BPF returned errno values wrong in VM?
Date: Thu, 13 Aug 2015 16:14:54 -0700	[thread overview]
Message-ID: <CAGXu5j+SQaMofhwqTFpCdo6wSAYLxKBA1M9cVAkUZKNE0FzwEQ@mail.gmail.com> (raw)
In-Reply-To: <CALCETrXGJQ33hDJ-GcVfrYx2qh0ewBwU5=o70UE=XuP+H2hz3g@mail.gmail.com>

On Thu, Aug 13, 2015 at 3:59 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Thu, Aug 13, 2015 at 3:56 PM, Kees Cook <keescook@chromium.org> wrote:
>> On Thu, Aug 13, 2015 at 3:54 PM, Linus Torvalds
>> <torvalds@linux-foundation.org> wrote:
>>> On Thu, Aug 13, 2015 at 3:49 PM, Linus Torvalds
>>> <torvalds@linux-foundation.org> wrote:
>>>>
>>>> Does the attached patch make sense and work?
>>>
>>> Btw, I'm not all that happy with it anyway.
>>>
>>> I still think Denys' patch also potentially changed what audit and
>>> strace see for %rax in the pt_regs to -ENOSYS, which I'm not convinced
>>> is a good change.
>>>
>>> But maybe that three-liner patch fixes the immediate problem that
>>> David sees. David?
>>
>> Your patch fixes it for me. The seccomp compat selftests pass again
>> with audit enabled.
>
> Kees, would it be straightforward to rig up the seccomp tests to
> automatically test compat?  The x86 selftests automatically test both
> native and compat, and that might be usable as a model.  I did that
> because it's extremely easy to regress one and not the other.

Yeah, I'll figure out how to get this working sanely. There are some
ugly behaviors on arm64 doing compat that seccomp found too, so I'll
need those targets for more than just x86.

-Kees

-- 
Kees Cook
Chrome OS Security