[PATCH v11 10/12] 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_exception() will emulate dummy results for these
instructions as follows: in virtual-8086 and protected modes, sgdt, sidt
and smsw are emulated; str and sldt are not emulated. No emulation is done
for user-space long mode processes.

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

Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Chen Yucong <slaoub@xxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Huang Rui <ray.huang@xxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
 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 9aab8b8..abf4f28 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -60,6 +60,7 @@
 #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>
@@ -513,6 +514,10 @@ 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 (static_cpu_has(X86_FEATURE_UMIP))
+		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);
-- 
2.7.4