Re: [v6 PATCH 19/21] x86/traps: Fixup general protection faults caused by UMIP

[Andy Lutomirski]

On Tue, Mar 7, 2017 at 4:32 PM, Ricardo Neri
 wrote:
> 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. 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.

Reviewed-by: Andy Lutomirski 
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[v6 PATCH 19/21] 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. 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 
Cc: Alexandre Julliard 
Cc: Stas Sergeev 
Cc: x...@kernel.org
Cc: linux-msdos@vger.kernel.org
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 948443e..86efbcb 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -65,6 +65,7 @@
 #include 
 #include 
 #include 
+#include 
 
 #ifdef CONFIG_X86_64
 #include 
@@ -492,6 +493,9 @@ 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);
-- 
2.9.3

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