On Fri, May 05, 2017 at 11:17:22AM -0700, Ricardo Neri 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 userspace to be protected from. Given the similarities in relevance, it
> makes sense to enable UMIP along with SMAP and SMEP.
>
> UMIP is enabled by default. It can be disabled by adding clearcpuid=514
> to the kernel parameters.
>
> Cc: Andy Lutomirski <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: H. Peter Anvin <[email protected]>
> Cc: Borislav Petkov <[email protected]>
> Cc: Brian Gerst <[email protected]>
> Cc: Chen Yucong <[email protected]>
> Cc: Chris Metcalf <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Fenghua Yu <[email protected]>
> Cc: Huang Rui <[email protected]>
> Cc: Jiri Slaby <[email protected]>
> Cc: Jonathan Corbet <[email protected]>
> Cc: Michael S. Tsirkin <[email protected]>
> Cc: Paul Gortmaker <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Ravi V. Shankar <[email protected]>
> Cc: Shuah Khan <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Cc: Tony Luck <[email protected]>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Liang Z. Li <[email protected]>
> Cc: Alexandre Julliard <[email protected]>
> Cc: Stas Sergeev <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Ricardo Neri <[email protected]>
> ---
> arch/x86/Kconfig | 10 ++++++++++
> arch/x86/kernel/cpu/common.c | 16 +++++++++++++++-
> 2 files changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 702002b..1b1bbeb 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1745,6 +1745,16 @@ config X86_SMAP
>
> If unsure, say Y.
>
> +config X86_INTEL_UMIP
> + def_bool y
That's a bit too much. It makes sense on distro kernels but how many
machines out there actually have UMIP?
> + 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.
> +
> config X86_INTEL_MPX
> prompt "Intel MPX (Memory Protection Extensions)"
> def_bool n
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 8ee3211..66ebded 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -311,6 +311,19 @@ static __always_inline void setup_smap(struct
> cpuinfo_x86 *c)
> }
> }
>
> +static __always_inline void setup_umip(struct cpuinfo_x86 *c)
> +{
> + if (cpu_feature_enabled(X86_FEATURE_UMIP) &&
> + cpu_has(c, X86_FEATURE_UMIP))
Hmm, so if UMIP is not build-time disabled, the cpu_feature_enabled()
will call static_cpu_has().
Looks like you want to call cpu_has() too because alternatives haven't
run yet and static_cpu_has() will reply wrong. Please state that in a
comment.
--
Regards/Gruss,
Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284
(AG Nürnberg)
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