linux-kernel - Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation

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 for Android: free password hash cracker in your pocket

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

Message-Id: <90B32DAE-0BB5-4455-8F73-C43037695E7C@gmail.com>
Date:   Tue, 7 Apr 2020 13:27:45 -0700
From:   Nadav Amit <nadav.amit@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, hch@...radead.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        mingo <mingo@...hat.com>, bp <bp@...en8.de>, hpa@...or.com,
        x86 <x86@...nel.org>, "Kenneth R. Crudup" <kenny@...ix.com>,
        Jessica Yu <jeyu@...nel.org>,
        Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Tony Luck <tony.luck@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        jannh@...gle.com, keescook@...omium.org, David.Laight@...lab.com,
        Doug Covelli <dcovelli@...are.com>, mhiramat@...nel.org
Subject: Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation

> On Apr 7, 2020, at 12:38 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Tue, Apr 07, 2020 at 11:55:21AM -0700, Nadav Amit wrote:
>>> On Apr 7, 2020, at 4:02 AM, Peter Zijlstra <peterz@...radead.org> wrote:
>>> 
>>> Since we now have infrastructure to analyze module text, disallow
>>> modules that write to CRn and DRn registers.
>> 
>> Assuming the kernel is built without CONFIG_PARAVIRT, what is the right way
>> for out-of-tree modules to write to CRs? Let’s say CR2?
> 
> Most of them there is no real justification for ever writing to. CR2 I
> suppose we can have an exception for given a sane rationale for why
> you'd need to rewrite the fault address.

For the same reason that KVM writes to CR2 - to restore CR2 before entering
a guest, since CR2 not architecturally loaded from the VMCS. I suspect there
are additional use-cases which are not covered by the kernel interfaces.