linux-kernel - Re: [PATCH v3 27/37] x86/shstk: Introduce routines modifying shstk

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: <Y3ZChDNwybrNKFX2@hirez.programming.kicks-ass.net>
Date:   Thu, 17 Nov 2022 15:17:40 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc:     "bsingharora@...il.com" <bsingharora@...il.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "Syromiatnikov, Eugene" <esyr@...hat.com>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
        "Eranian, Stephane" <eranian@...gle.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "fweimer@...hat.com" <fweimer@...hat.com>,
        "nadav.amit@...il.com" <nadav.amit@...il.com>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "dethoma@...rosoft.com" <dethoma@...rosoft.com>,
        "kcc@...gle.com" <kcc@...gle.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "bp@...en8.de" <bp@...en8.de>, "oleg@...hat.com" <oleg@...hat.com>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "Yang, Weijiang" <weijiang.yang@...el.com>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "jamorris@...ux.microsoft.com" <jamorris@...ux.microsoft.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "pavel@....cz" <pavel@....cz>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "rppt@...nel.org" <rppt@...nel.org>,
        "john.allen@....com" <john.allen@....com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "corbet@....net" <corbet@....net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "gorcunov@...il.com" <gorcunov@...il.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 27/37] x86/shstk: Introduce routines modifying shstk

On Wed, Nov 16, 2022 at 10:38:19PM +0000, Edgecombe, Rick P wrote:
> On Wed, 2022-11-16 at 11:18 +0100, Peter Zijlstra wrote:
> > > > 
> > > > Should you write a 64bit value even if the task receiving a
> > > > signal is
> > > > 32bit ?
> > > 
> > > 32 bit support was also dropped.
> > 
> > How? Task could start life as 64bit, frob LDT to set up 32bit code
> > segment and jump into it and start doing 32bit syscalls, then what?
> > 
> > AFAICT those 32bit syscalls will end up doing SA_IA32_ABI sigframes.
> 
> Hmm, good point. This series used to support normal 32 bit apps via
> ia32 emulation which would have handled this. But I removed it (blocked
> in the enabling logic) because it didn't seem like it would get enough
> use to justify the extra code. That doesn't block this scenario here
> though.
> 
> Pardon the possibly naive question, but is this 32/64 bit mixing
> something any normal, shstk-desiring, applications would actually do? O
> r more that they could do?

It is not something common, but it is something that things like Wine
do IIRC, and it would be a real shame if Wine could not use shadow
stacks or something, right ;-)

But more to the point; since the kernel cannot forbit this scenario
(aside from taking away the LDT entirely) it is something that needs
handling.