linux-kernel - Re: [PATCH 05/11] x86/fpu: set PKRU state for kernel threads

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <39e0a55f-4920-cfde-9bef-09c51109d211@linux.intel.com>
Date:   Fri, 12 Oct 2018 10:54:05 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH 05/11] x86/fpu: set PKRU state for kernel threads

On 10/04/2018 07:05 AM, Sebastian Andrzej Siewior wrote:
> The PKRU value is not set for kernel threads because they do not have
> the ->initialized value set. As a result the kernel thread has a random
> PKRU value set which it inherits from the previous task.
> It has been suggested by Paolo Bonzini to set it for kernel threads, too
> because it might be a fix.
> I *think* this is not required because the kernel threads don't copy
> data to/from userland and don't have access to any userspace mm in
> general.
> However there is this use_mm(). If we gain a mm by use_mm() we don't
> have a matching PKRU value because those are per thread. It has been
> suggested to use 0 as the PKRU value but this would bypass PKRU.
> 
> Set the initial (default) PKRU value for kernel threads.

We might want to do this for cleanliness reasons...  Maybe.

But this *should* have no practical effects.  Kernel threads have no
real 'mm' and no user pages.  They should not have do access to user
mappings.  Protection keys *only* apply to user mappings.  Thus,
logically, they should never be affected by PKRU values.

So I'm kinda missing the point of the patch.