linux-kernel - Re: [PATCH 2/5] uaccess: Add speculation barrier to copy_from_user

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: <2f569008-dd66-4bb6-bf5e-f2317bb95e10@csgroup.eu>
Date: Tue, 24 Jun 2025 07:49:03 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin
 <npiggin@...il.com>, Naveen N Rao <naveen@...nel.org>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, Darren Hart <dvhart@...radead.org>,
 Davidlohr Bueso <dave@...olabs.net>, Andre Almeida <andrealmeid@...lia.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 David Laight <david.laight.linux@...il.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, linux-kernel@...r.kernel.org,
 linuxppc-dev@...ts.ozlabs.org, linux-fsdevel@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [PATCH 2/5] uaccess: Add speculation barrier to
 copy_from_user_iter()



Le 22/06/2025 à 18:57, Linus Torvalds a écrit :
> On Sun, 22 Jun 2025 at 02:52, Christophe Leroy
> <christophe.leroy@...roup.eu> wrote:
>>
>> The results of "access_ok()" can be mis-speculated.
> 
> Hmm. This code is critical. I think it should be converted to use that
> masked address thing if we have to add it here.

Ok, I'll add it.

> 
> And at some point this access_ok() didn't even exist, because we check
> the addresses at iter creation time. So this one might be a "belt and
> suspenders" check, rather than something critical.
> 
> (Although I also suspect that when we added ITER_UBUF we might have
> created cases where those user addresses aren't checked at iter
> creation time any more).
> 

Let's take the follow path as an exemple:

snd_pcm_ioctl(SNDRV_PCM_IOCTL_WRITEI_FRAMES)
   snd_pcm_common_ioctl()
     snd_pcm_xferi_frames_ioctl()
       snd_pcm_lib_write()
         __snd_pcm_lib_xfer()
           default_write_copy()
             copy_from_iter()
               _copy_from_iter()
                 __copy_from_iter()
                   iterate_and_advance()
                     iterate_and_advance2()
                       iterate_iovec()
                         copy_from_user_iter()

As far as I can see, none of those functions check the accessibility of 
the iovec. Am I missing something ?

Christophe