Messages in this thread | | | Date | Wed, 12 Apr 2023 10:02:15 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH 2/2] s390/stackleak: provide fast __stackleak_poison() implementation |
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On Wed, Apr 05, 2023 at 03:08:41PM +0200, Heiko Carstens wrote: > Provide an s390 specific __stackleak_poison() implementation which is > faster than the generic variant. > > For the original implementation with an enforced 4kb stackframe for the > getpid() system call the system call overhead increases by a factor of 3 if > the stackleak feature is enabled. Using the s390 mvc based variant this is > reduced to an increase of 25% instead. > > This is within the expected area, since the mvc based implementation is > more or less a memset64() variant which comes with similar results. See > commit 0b77d6701cf8 ("s390: implement memset16, memset32 & memset64").
With that in mind, could we use memset64() directly (if we made it noninstr-safe)?
Mark.
> > Reviewed-by: Vasily Gorbik <gor@linux.ibm.com> > Signed-off-by: Heiko Carstens <hca@linux.ibm.com> > --- > arch/s390/include/asm/processor.h | 35 +++++++++++++++++++++++++++++++ > 1 file changed, 35 insertions(+) > > diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h > index efffc28cbad8..dc17896a001a 100644 > --- a/arch/s390/include/asm/processor.h > +++ b/arch/s390/include/asm/processor.h > @@ -118,6 +118,41 @@ unsigned long vdso_size(void); > > #define HAVE_ARCH_PICK_MMAP_LAYOUT > > +#define __stackleak_poison __stackleak_poison > +static __always_inline void __stackleak_poison(unsigned long erase_low, > + unsigned long erase_high, > + unsigned long poison) > +{ > + unsigned long tmp, count; > + > + count = erase_high - erase_low; > + if (!count) > + return; > + asm volatile( > + " cghi %[count],8\n" > + " je 2f\n" > + " aghi %[count],-(8+1)\n" > + " srlg %[tmp],%[count],8\n" > + " ltgr %[tmp],%[tmp]\n" > + " jz 1f\n" > + "0: stg %[poison],0(%[addr])\n" > + " mvc 8(256-8,%[addr]),0(%[addr])\n" > + " la %[addr],256(%[addr])\n" > + " brctg %[tmp],0b\n" > + "1: stg %[poison],0(%[addr])\n" > + " larl %[tmp],3f\n" > + " ex %[count],0(%[tmp])\n" > + " j 4f\n" > + "2: stg %[poison],0(%[addr])\n" > + " j 4f\n" > + "3: mvc 8(1,%[addr]),0(%[addr])\n" > + "4:\n" > + : [addr] "+&a" (erase_low), [count] "+&d" (count), [tmp] "=&a" (tmp) > + : [poison] "d" (poison) > + : "memory", "cc" > + ); > +} > + > /* > * Thread structure > */ > -- > 2.37.2 >
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