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 0b77d6701cf8 ("s390: implement memset16, memset32 & memset64").
Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20230405130841.1350565-3-hca@linux.ibm.com
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index efffc28..dc17896 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -118,6 +118,41 @@
#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
*/
