linux-kernel - Re: [PATCH v2] x86/mm/pti: in pti_clone

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: <alpine.DEB.2.21.1908211210160.2223@nanos.tec.linutronix.de>
Date:   Wed, 21 Aug 2019 12:17:00 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Song Liu <songliubraving@...com>
cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Kernel Team <Kernel-team@...com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Joerg Roedel <jroedel@...e.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2] x86/mm/pti: in pti_clone_pgtable(), increase addr
 properly

On Wed, 21 Aug 2019, Song Liu wrote:
> > On Aug 20, 2019, at 1:23 PM, Song Liu <songliubraving@...com> wrote:
> > 
> > Before 32-bit support, pti_clone_pmds() always adds PMD_SIZE to addr.
> > This behavior changes after the 32-bit support:  pti_clone_pgtable()
> > increases addr by PUD_SIZE for pud_none(*pud) case, and increases addr by
> > PMD_SIZE for pmd_none(*pmd) case. However, this is not accurate because
> > addr may not be PUD_SIZE/PMD_SIZE aligned.
> > 
> > Fix this issue by properly rounding up addr to next PUD_SIZE/PMD_SIZE
> > in these two cases.
> 
> After poking around more, I found the following doesn't really make 
> sense. 

I'm glad you figured that out yourself. Was about to write up something to
that effect.

Still interesting questions remain:

  1) How did you end up feeding an unaligned address into that which points
     to a 0 PUD?

  2) Is this related to Facebook specific changes and unlikely to affect any
     regular kernel? I can't come up with a way to trigger that in mainline

  3) As this is a user page table and the missing mapping is related to
     mappings required by PTI, how is the machine going in/out of user
     space in the first place? Or did I just trip over what you called
     nonsense?

Thanks,

	tglx