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

[Dave Jones]

On Fri, Sep 21, 2012 at 12:43:04PM -0700, H. Peter Anvin 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:
 > 
 > http://software.intel.com/sites/default/files/319433-014.pdf
 > 
 > When SMAP is active, the kernel cannot normally access pages that are
 > user space (U=1).  Since the kernel does have the need to access user
 > space pages under specific circumstances, an override is provided: the
 > kernel can access user space pages if EFLAGS.AC=1.  For system data
 > structures, e.g. descriptor tables, that are accessed by the processor
 > directly, SMAP is active even in CPL 3 regardless of EFLAGS.AC.
 > 
 > SMAP also includes two new instructions, STAC and CLAC, to flip the AC
 > flag more quickly.

Perhaps add a printk somewhere to show that it's actually been enabled maybe ?

Also, would it be feasible to add something like we have for test_nx ?
If this feature regresses in some way in the future, I suspect we'd like
to know about it sooner rather than later.

	Dave

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