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 <l...@kernel.org>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: H. Peter Anvin <h...@zytor.com>
> Cc: Borislav Petkov <b...@suse.de>
> Cc: Brian Gerst <brge...@gmail.com>
> Cc: Chen Yucong <sla...@gmail.com>
> Cc: Chris Metcalf <cmetc...@mellanox.com>
> Cc: Dave Hansen <dave.han...@linux.intel.com>
> Cc: Fenghua Yu <fenghua...@intel.com>
> Cc: Huang Rui <ray.hu...@amd.com>
> Cc: Jiri Slaby <jsl...@suse.cz>
> Cc: Jonathan Corbet <cor...@lwn.net>
> Cc: Michael S. Tsirkin <m...@redhat.com>
> Cc: Paul Gortmaker <paul.gortma...@windriver.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Ravi V. Shankar <ravi.v.shan...@intel.com>
> Cc: Shuah Khan <sh...@kernel.org>
> Cc: Vlastimil Babka <vba...@suse.cz>
> Cc: Tony Luck <tony.l...@intel.com>
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: Liang Z. Li <liang.z...@intel.com>
> Cc: Alexandre Julliard <julli...@winehq.org>
> Cc: Stas Sergeev <s...@list.ru>
> Cc: x...@kernel.org
> Cc: linux-msdos@vger.kernel.org
> Signed-off-by: Ricardo Neri <ricardo.neri-calde...@linux.intel.com>
> ---
>  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 Imend├Ârffer, Jane Smithard, Graham Norton, HRB 21284 
(AG N├╝rnberg)
-- 
--
To unsubscribe from this list: send the line "unsubscribe linux-msdos" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Reply via email to