Re: [PATCH v4 26/35] s390/diag: Unpoison diag224() output buffer

[Alexander Potapenko]

On Thu, Jun 13, 2024 at 5:40 PM Ilya Leoshkevich  wrote:
>
> Diagnose 224 stores 4k bytes, which currently cannot be deduced from
> the inline assembly constraints. This leads to KMSAN false positives.
>
> Fix the constraints by using a 4k-sized struct instead of a raw
> pointer. While at it, prettify them too.
>
> Suggested-by: Heiko Carstens 
> Signed-off-by: Ilya Leoshkevich 
Reviewed-by: Alexander Potapenko 

[PATCH v4 26/35] s390/diag: Unpoison diag224() output buffer

[Ilya Leoshkevich]

Diagnose 224 stores 4k bytes, which currently cannot be deduced from
the inline assembly constraints. This leads to KMSAN false positives.

Fix the constraints by using a 4k-sized struct instead of a raw
pointer. While at it, prettify them too.

Suggested-by: Heiko Carstens 
Signed-off-by: Ilya Leoshkevich 
---
 arch/s390/kernel/diag.c | 10 ++
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/s390/kernel/diag.c b/arch/s390/kernel/diag.c
index 8dee9aa0ec95..8a7009618ba7 100644
--- a/arch/s390/kernel/diag.c
+++ b/arch/s390/kernel/diag.c
@@ -278,12 +278,14 @@ int diag224(void *ptr)
int rc = -EOPNOTSUPP;
 
diag_stat_inc(DIAG_STAT_X224);
-   asm volatile(
-   "   diag%1,%2,0x224\n"
-   "0: lhi %0,0x0\n"
+   asm volatile("\n"
+   "   diag%[type],%[addr],0x224\n"
+   "0: lhi %[rc],0\n"
"1:\n"
EX_TABLE(0b,1b)
-   : "+d" (rc) :"d" (0), "d" (addr) : "memory");
+   : [rc] "+d" (rc)
+   , "=m" (*(struct { char buf[PAGE_SIZE]; } *)ptr)
+   : [type] "d" (0), [addr] "d" (addr));
return rc;
 }
 EXPORT_SYMBOL(diag224);
-- 
2.45.1