Re: [PATCH v7 23/26] x86/traps: Fixup general protection faults caused by UMIP

[Ricardo Neri]

I am sorry Boris, I also missed this feedback.

On Fri, 2017-06-09 at 15:02 +0200, Borislav Petkov wrote:
> On Fri, May 05, 2017 at 11:17:21AM -0700, 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
> 
> Please end function names with parentheses.

I have audited my commit messages to remove all instances of this error.
> 
> > 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
> > Reviewed-by: Andy Lutomirski 
> > 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 3995d3a..cec548d 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 
> > @@ -526,6 +527,9 @@ 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);
> >  
> 
> Almost definitely:
> 
>   if (static_cpu_has(X86_FEATURE_UMIP)) {
>   if (...

I will make this update.

> 
> > +   if (user_mode(regs) && fixup_umip_exception(regs))
> > +   return;
> 
> We don't want to punish !UMIP machines.

I will add this check.

Thanks and BR,
Ricardo

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Re: [PATCH v7 23/26] x86/traps: Fixup general protection faults caused by UMIP

[Borislav Petkov]

On Fri, May 05, 2017 at 11:17:21AM -0700, 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

Please end function names with parentheses.

> 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
> Reviewed-by: Andy Lutomirski 
> 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 3995d3a..cec548d 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 
> @@ -526,6 +527,9 @@ 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);
>  

Almost definitely:

if (static_cpu_has(X86_FEATURE_UMIP)) {
if (...

> + if (user_mode(regs) && fixup_umip_exception(regs))
> + return;

We don't want to punish !UMIP machines.

-- 
Regards/Gruss,
Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 
(AG Nürnberg)
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[PATCH v7 23/26] 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
Reviewed-by: Andy Lutomirski 
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 3995d3a..cec548d 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 
@@ -526,6 +527,9 @@ 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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