Commit 2a405f6b authored by Heiko Carstens's avatar Heiko Carstens Committed by Vasily Gorbik
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s390/stackleak: provide fast __stackleak_poison() implementation 



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 0b77d670 ("s390: implement memset16, memset32 & memset64").

Reviewed-by: default avatarVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20230405130841.1350565-3-hca@linux.ibm.com


Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
parent 491a7866

arch/s390/include/asm/processor.h

+35 −0
Original line number Diff line number Diff line
@@ -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

 */