* Ricardo Neri <[email protected]> wrote:
> User-Mode Instruction Prevention (UMIP) is enabled by setting/clearing a
> bit in %cr4.
>
> It makes sense to enable UMIP at some point while booting, before user
> spaces come up. Like SMAP and SMEP, is not critical to have it enabled
> very early during boot. This is because UMIP is relevant only when there is
> a user space to be protected from. Given these similarities, UMIP can be
> enabled along with SMAP and SMEP.
>
> At the moment, UMIP is disabled by default at build time. It can be enabled
> at build time by selecting CONFIG_X86_INTEL_UMIP. If enabled at build time,
> it can be disabled at run time by adding clearcpuid=514 to the kernel
> parameters.
> +config X86_INTEL_UMIP
> + def_bool n
> + depends on CPU_SUP_INTEL
> + prompt "Intel User Mode Instruction Prevention" if EXPERT
> + ---help---
> + The User Mode Instruction Prevention (UMIP) is a security
> + feature in newer Intel processors. If enabled, a general
> + protection fault is issued if the instructions SGDT, SLDT,
> + SIDT, SMSW and STR are executed in user mode.
Ok, I really like this latest series.
One small request: could you please make the feature default-y, which is what
we
do for new hardware features that don't have a significant runtime cost.
There's
no ABI breakage expected, right?
Another request: could you please extend the Kconfig description to _explain_
to
the user why this feature is useful - in a short sentence or so. I.e. point out
that these instructions expose information about hardware state that is not
really
necessary for the vast majority of applications.
Plus:
> + cr4_set_bits(X86_CR4_UMIP);
Please also inform admins that it's enabled, via something like:
pr_info("x86/cpu: Activated the Intel User Mode Instruction Prevention
(UMIP) CPU feature\n");
... or so.
Please do these changes in a separate add-on patch #13 on top of this series,
as
I've already started testing these bits.
Thanks,
Ingo
