[v2 6/7] x86/traps: Fixup general protection faults caused by UMIP

[Ricardo Neri]

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_exceptino will emulate dummy results for these
instructions.

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: [e-mail]
Cc: [e-mail]
Signed-off-by: Ricardo Neri 
---
 arch/x86/kernel/traps.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index bf0c6d0..5044fb3 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -64,6 +64,7 @@
 #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>
@@ -491,6 +492,9 @@ do_general_protection(struct pt_regs *regs, long error_code)
    RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
    cond_local_irq_enable(regs);

+	if (user_mode(regs) && !fixup_umip_exception(regs))
+		return;
+
    if (v8086_mode(regs)) {
    	local_irq_enable();
    	handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code);