stcctm() uses the "Q" constraint for dest, therefore KMSAN does not
understand that it fills multiple doublewords pointed to by dest, not
just one. This results in false positives.

Unpoison the whole dest manually with kmsan_unpoison_memory().

Reported-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 arch/s390/include/asm/cpu_mf.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/s390/include/asm/cpu_mf.h b/arch/s390/include/asm/cpu_mf.h
index a0de5b9b02ea..9e4bbc3e53f8 100644
--- a/arch/s390/include/asm/cpu_mf.h
+++ b/arch/s390/include/asm/cpu_mf.h
@@ -10,6 +10,7 @@
 #define _ASM_S390_CPU_MF_H
 
 #include <linux/errno.h>
+#include <linux/kmsan-checks.h>
 #include <asm/asm-extable.h>
 #include <asm/facility.h>
 
@@ -239,6 +240,11 @@ static __always_inline int stcctm(enum stcctm_ctr_set set, u64 range, u64 *dest)
 		: "=d" (cc)
 		: "Q" (*dest), "d" (range), "i" (set)
 		: "cc", "memory");
+	/*
+	 * If cc == 2, less than RANGE counters are stored, but it's not easy
+	 * to tell how many. Always unpoison the whole range for simplicity.
+	 */
+	kmsan_unpoison_memory(dest, range * sizeof(u64));
 	return cc;
 }
 
-- 
2.43.0

On Thu, Dec 14, 2023 at 12:24:44AM +0100, Ilya Leoshkevich wrote:
> stcctm() uses the "Q" constraint for dest, therefore KMSAN does not
> understand that it fills multiple doublewords pointed to by dest, not
> just one. This results in false positives.
> 
> Unpoison the whole dest manually with kmsan_unpoison_memory().
> 
> Reported-by: Alexander Gordeev <agordeev@linux.ibm.com>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  arch/s390/include/asm/cpu_mf.h | 6 ++++++
>  1 file changed, 6 insertions(+)

Acked-by: Heiko Carstens <hca@linux.ibm.com>

On Thu, Dec 14, 2023 at 12:37 AM Ilya Leoshkevich <iii@linux.ibm.com> wrote:
>
> stcctm() uses the "Q" constraint for dest, therefore KMSAN does not
> understand that it fills multiple doublewords pointed to by dest, not
> just one. This results in false positives.
>
> Unpoison the whole dest manually with kmsan_unpoison_memory().
>
> Reported-by: Alexander Gordeev <agordeev@linux.ibm.com>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>