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  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]
Date:	Sat, 04 Nov 2006 11:39:08 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Zachary Amsden <zach@...are.com>
Cc:	Chuck Ebbert <76306.1226@...puserve.com>, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...l.org>,
	Linus Torvalds <torvalds@...l.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch] i386: remove IOPL check on task switch

Zachary Amsden wrote:
> Chuck Ebbert wrote:
>> In-Reply-To: <454B850C.3050402@...are.com>
>>
>> On Fri, 03 Nov 2006 10:06:04 -0800, Zachary Amsden wrote:
>>
>>  
>>> Chuck Ebbert wrote:
>>>    
>>>> IOPL is implicitly saved and restored on task switch,
>>>> so explicit check is no longer needed.
>>>>       
>>> Nack.  This is used for paravirt-ops kernels that use IOPL'd 
>>> userspace.      
>>
>> How does that work?  In the stock kernel, anything done by
>> the call to set_iopl_mask() (that was removed by the patch)
>> will be nullified by the 'popfl' at the end of the switch_to()
>> macro.
>>   
>
> Who put a popfl back in switch_to?  I took it out some time ago.  It 
> should not be there.  The only reason for it was to stop IOPL leaking 
> from one process to another from a sleep during a sysenter based 
> system call.

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.

Zach
-
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/

Powered by blists - more mailing lists