From: Zachary Amsden <zach@vmware.com>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Chuck Ebbert <76306.1226@compuserve.com>, Andi Kleen <ak@suse.de>,
Andrew Morton <akpm@osdl.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [patch] i386: remove IOPL check on task switch
Date: Sat, 04 Nov 2006 12:09:44 -0800 [thread overview]
Message-ID: <454CF388.509@vmware.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0611041152060.25218@g5.osdl.org>
Linus Torvalds wrote:
> On Sat, 4 Nov 2006, Zachary Amsden wrote:
>
>> Ok, checking shows Linus put it back to stop NT leakage. This is correct, but
>> unlikely. Would be nice to avoid it unless absolutely necessary. Perhaps xor
>> eflags old and new and only set_system_eflags() if non-ALU bits have changed.
>>
>
> Not just NT. AC also leaked, and caused crashes in other programs (Wine)
> that didn't expect AC to be set and did unaligned accesses.
Yes, AC, NT, IOPL, ID are bad to leak. DF / TF / RF are impossible to
leak by privilege contract. SF, ZF, PF, OF, CF can be clobbered.
VM / VIF / VIP are dealt with in separate switch paths (although I have
witnessed a VIF leak once from a userspace process that managed to get
VIF set). These can't even be set with popf, and require iret to fix.
But 99% of the time, only SF / ZF / PF / OF / CF will be different, so
you can avoid the popf.
Zach
next prev parent reply other threads:[~2006-11-04 20:09 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-11-03 23:57 [patch] i386: remove IOPL check on task switch Chuck Ebbert
2006-11-04 19:19 ` Zachary Amsden
2006-11-04 19:39 ` Zachary Amsden
2006-11-04 19:52 ` Linus Torvalds
2006-11-04 20:09 ` Zachary Amsden [this message]
2006-11-04 20:02 ` Andi Kleen
-- strict thread matches above, loose matches on Subject: below --
2006-11-04 0:00 Chuck Ebbert
2006-11-03 6:27 Chuck Ebbert
2006-11-03 18:06 ` Zachary Amsden
2006-11-03 18:41 ` Andi Kleen
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