linux-kernel - Re: [PATCH 10/20] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.

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Message-ID: <87r1ce8g5i.fsf@disp2133>
Date:   Thu, 21 Oct 2021 12:02:49 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, H Peter Anvin <hpa@...or.com>
Subject: Re: [PATCH 10/20] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.

Kees Cook <keescook@...omium.org> writes:

> On Wed, Oct 20, 2021 at 12:43:56PM -0500, Eric W. Biederman wrote:
>> Instead of pretending to send SIGSEGV by calling do_exit(SIGSEGV)
>> call force_sigsegv(SIGSEGV) to force the process to take a SIGSEGV
>> and terminate.
>> 
>> Update handle_signal to return immediately when save_v86_state fails
>> and kills the process.  Returning immediately without doing anything
>> except killing the process with SIGSEGV is also what signal_setup_done
>> does when setup_rt_frame fails.  Plus it is always ok to return
>> immediately without delivering a signal to a userspace handler when a
>> fatal signal has killed the current process.
>
> Do the tools/testing/selftests/x86 tests all pass after these changes? I
> know Andy has a bunch of weird corner cases in there.

That would require a 32bit userspace wouldn't it?

It is a good idea so I will see if I can dig such a box up, but I
unfortunately don't have an up-to-date 32bit box handy, or even
an up-to-date box with a 32bit userspace.

It has been about 20 years since I have done much with 32bit x86.

How hard is it to run the tests under tools/testing/selftests/...
Last time I tried it was a royal pain.  I am hoping it is better this
round.

Eric