On Fri, 2017-06-09 at 18:10 +0200, Borislav Petkov wrote: > 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-ms...@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?
So would this become a y when more machines 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. Why would static_cpu_has() reply wrong if alternatives are not in place? Because it uses the boot CPU data? When it calls _static_cpu_has() it would do something equivalent to testb test_bit, boot_cpu_data.x86_capability[bit]. I am calling cpu_has because cpu_feature_enabled(), via static_cpu_has(), will use the boot CPU data while cpu_has would use the local CPU data. Is this what you meant? I can definitely add a comment with this explanation, if it makes sense. Thanks and BR, Ricardo