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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