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Subject[PATCH v8 26/28] x86/traps: Fixup general protection faults caused by UMIP
If the User-Mode Instruction Prevention CPU feature is available and
enabled, a general protection fault will be issued if the instructions
sgdt, sldt, sidt, str or smsw are executed from user-mode context
(CPL > 0). If the fault was caused by any of the instructions protected
by UMIP, fixup_umip_exception() will emulate dummy results for these
instructions as follows: if running a 32-bit process, sgdt, sidt and smsw
are emulated; str and sldt are not emulated. No emulation is done for
64-bit processes.

If emulation is successful, the result is passed to the user space program
and no SIGSEGV signal is emitted.

Please note that fixup_umip_exception() also caters for the case when
the fault originated while running in virtual-8086 mode.

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 <>
Reviewed-by: Andy Lutomirski <>
Signed-off-by: Ricardo Neri <>
arch/x86/kernel/traps.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index bf54309b85da..1c1bb7992f70 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -65,6 +65,7 @@
#include <asm/trace/mpx.h>
#include <asm/mpx.h>
#include <asm/vm86.h>
+#include <asm/umip.h>

#ifdef CONFIG_X86_64
#include <asm/x86_init.h>
@@ -526,6 +527,10 @@ do_general_protection(struct pt_regs *regs, long error_code)
RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");

+ if (static_cpu_has(X86_FEATURE_UMIP))
+ if (user_mode(regs) && fixup_umip_exception(regs))
+ return;
if (v8086_mode(regs)) {
handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code);
 \ /
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