linux-kernel - Re: [PATCH v3 3/4] uaccess: Check no rescheduling function is called in unsafe region

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: <dd33cc20-f335-0e4c-e3f4-02497ecc3710@arm.com>
Date:   Wed, 13 Feb 2019 14:39:22 +0000
From:   Julien Thierry <julien.thierry@....com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, mingo@...hat.com,
        catalin.marinas@....com, james.morse@....com, hpa@...or.com,
        valentin.schneider@....com
Subject: Re: [PATCH v3 3/4] uaccess: Check no rescheduling function is called
 in unsafe region

Hi Peter,

On 13/02/2019 14:25, Peter Zijlstra wrote:
> On Wed, Feb 13, 2019 at 02:00:26PM +0000, Will Deacon wrote:
>> The difference is because getting preempted in the sequence above is
>> triggered off the back of an interrupt. On arm64, and I think also on x86,
>> the user access state (SMAP or PAN) is saved and restored across exceptions
>> but not across context switch.
> 
> A quick reading of the SDM seems to suggest the SMAP state is part of
> EFLAGS, which is context switched just fine AFAIK.
> 
I fail to see where this is happening when looking at the switch_to()
logic in x86_64.

And Peter A. didn't seem to suggest that this transfer of the eflags was
happening without them being saved on the stack through exception handling.

What am I missing?

Thanks,

-- 
Julien Thierry