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 <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: Liang Z. Li <liang.z.li@xxxxxxxxx>
> > Cc: Alexandre Julliard <julliard@xxxxxxxxxx>
> > Cc: Stas Sergeev <stsp@xxxxxxx>
> > Cc: x86@xxxxxxxxxx
> > Cc: linux-msdos@xxxxxxxxxxxxxxx
> > Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx>
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> > ---
> >  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 <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 +527,9 @@ 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