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
Cc: Andrew Morton
Cc: H. Peter Anvin
Cc: Borislav Petkov
Cc: Brian Gerst
Cc: Chen Yucong
Cc: Chris Metcalf
Cc: Dave Hansen
Cc: Fenghua Yu
Cc: Huang Rui
Cc: Jiri Slaby
Cc: Jonathan Corbet
Cc: Michael S. Tsirkin
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Ravi V. Shankar
Cc: Shuah Khan
Cc: Vlastimil Babka
Cc: Tony Luck
Cc: Paolo Bonzini
Cc: Liang Z. Li
Cc: Alexandre Julliard
Cc: Stas Sergeev
Cc: x...@kernel.org
Cc: linux-msdos@vger.kernel.org
Signed-off-by: Ricardo Neri
---
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 e487493..bae1a8f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1733,6 +1733,16 @@ config X86_SMAP
If unsure, say Y.
+config X86_INTEL_UMIP
+ def_bool y
+ depends on CPU_SUP_INTEL
+ prompt "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 dc1697c..b38a639 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -306,6 +306,19 @@ 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))
+ cr4_set_bits(X86_CR4_UMIP);
+ else
+ /*
+* Make sure UMIP is disabled in case it was enabled in a
+* previous boot (e.g., via kexec).
+*/
+ cr4_clear_bits(X86_CR4_UMIP);
+}
+
/*
* Protection Keys are not available in 32-bit mode.
*/
@@ -1059,9 +1072,10 @@ static void identify_cpu(struct cpuinfo_x86 *c)
/* Disable the PN if appropriate */
squash_the_stupid_serial_number(c);
- /* Set up SMEP/SMAP */
+ /* Set up SMEP/SMAP/UMIP */
setup_smep(c);
setup_smap(c);
+ setup_umip(c);
/*
* The vendor-specific functions might have changed features.
--
2.9.3
--
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