From 674c5ff0f440a051ebf299d29a4c013133d81a65 Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Mon, 2 Mar 2026 14:35:00 +0100 Subject: [PATCH] s390/stackleak: Fix __stackleak_poison() inline assembly constraint The __stackleak_poison() inline assembly comes with a "count" operand where the "d" constraint is used. "count" is used with the exrl instruction and "d" means that the compiler may allocate any register from 0 to 15. If the compiler would allocate register 0 then the exrl instruction would not or the value of "count" into the executed instruction - resulting in a stackframe which is only partially poisoned. Use the correct "a" constraint, which excludes register 0 from register allocation. Fixes: 2a405f6bb3a5 ("s390/stackleak: provide fast __stackleak_poison() implementation") Cc: stable@vger.kernel.org Signed-off-by: Heiko Carstens Reviewed-by: Vasily Gorbik Link: https://lore.kernel.org/r/20260302133500.1560531-4-hca@linux.ibm.com Signed-off-by: Vasily Gorbik --- arch/s390/include/asm/processor.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h index cc187afa07b3..78195ee5e99f 100644 --- a/arch/s390/include/asm/processor.h +++ b/arch/s390/include/asm/processor.h @@ -159,7 +159,7 @@ static __always_inline void __stackleak_poison(unsigned long erase_low, " j 4f\n" "3: mvc 8(1,%[addr]),0(%[addr])\n" "4:" - : [addr] "+&a" (erase_low), [count] "+&d" (count), [tmp] "=&a" (tmp) + : [addr] "+&a" (erase_low), [count] "+&a" (count), [tmp] "=&a" (tmp) : [poison] "d" (poison) : "memory", "cc" );