linux-kernel - Re: [PATCH 00/11] x86: Supervisor Mode Access Prevention

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Date:	Fri, 21 Sep 2012 14:03:37 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Kees Cook <keescook@...omium.org>,
	Linda Wang <lwang@...hat.com>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH 00/11] x86: Supervisor Mode Access Prevention

On 09/21/2012 01:08 PM, Ingo Molnar wrote:
> 
> * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
>> On Fri, Sep 21, 2012 at 12:43 PM, H. Peter Anvin <hpa@...ux.intel.com> wrote:
>>
>>> Supervisor Mode Access Prevention (SMAP) is a new security 
>>> feature disclosed by Intel in revision 014 of the Intel® 
>>> Architecture Instruction Set Extensions Programming 
>>> Reference:
>>
>> Looks good.
>>
>> Did this find any bugs, btw? We've had a few cases where we 
>> forgot to use the proper user access function, and code just 
>> happened to work because it all boils down to the same thing 
>> and never got any page faults in practice anyway..
> 
> The 4g:4g patch sweeped out most of the historic ones - so what 
> we have are perhaps newer bugs (but those should be pretty rare, 
> most new features are cross-arch).
> 

A while ago I also did a mockup patch which switched %cr3 to
swapper_pg_dir while entering the kernel (basically where the CLAC
instructions go, plus the SYSCALL path; a restore was obviously needed,
too.)  The performance was atrocious, but I didn't remember running into
any problems.

	-hpa

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