linux-kernel - Re: [PATCH] x86/cpu: Fix SMAP check in PVOPS environments

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: <556FF270.5060306@zytor.com>
Date:	Wed, 03 Jun 2015 23:38:40 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andrew Cooper <andrew.cooper3@...rix.com>,
	Xen-devel <xen-devel@...ts.xen.org>
CC:	David Vrabel <david.vrabel@...rix.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	lguest@...ts.ozlabs.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86/cpu: Fix SMAP check in PVOPS environments

On 06/03/2015 02:31 AM, Andrew Cooper wrote:
> There appears to be no formal statement of what pv_irq_ops.save_fl() is
> supposed to return precisely.  Native returns the full flags, while lguest and
> Xen only return the Interrupt Flag, and both have comments by the
> implementations stating that only the Interrupt Flag is looked at.  This may
> have been true when initially implemented, but no longer is.
> 
> To make matters worse, the Xen PVOP leaves the upper bits undefined, making
> the BUG_ON() undefined behaviour.  Experimentally, this now trips for 32bit PV
> guests on Broadwell hardware.  The BUG_ON() is consistent for an individual
> build, but not consistent for all builds.  It has also been a sitting timebomb
> since SMAP support was introduced.
> 
> Use native_save_fl() instead, which will obtain an accurate view of the AC
> flag.

Could we fix the Xen pvops wrapper instead to not do things like this?

	-hpa


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/