KVM: s390: selftest: memop: Fix undefined behavior

Nina Schoetterl-Glausch · frankjaa · commit 00de073e2420 · 2024-02-23T14:02:27.000+01:00
If an integer's type has x bits, shifting the integer left by x or more is undefined behavior. This can happen in the rotate function when attempting to do a rotation of the whole value by 0. Fixes: 0dd714b ("KVM: s390: selftest: memop: Add cmpxchg tests") Signed-off-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com> Link: https://lore.kernel.org/r/20240111094805.363047-1-nsg@linux.ibm.com Acked-by: Janosch Frank <frankja@linux.ibm.com> Signed-off-by: Janosch Frank <frankja@linux.ibm.com> Message-Id: <20240111094805.363047-1-nsg@linux.ibm.com>
diff --git a/tools/testing/selftests/kvm/s390x/memop.c b/tools/testing/selftests/kvm/s390x/memop.c
@@ -489,6 +489,8 @@ static __uint128_t rotate(int size, __uint128_t val, int amount)
 
 	amount = (amount + bits) % bits;
 	val = cut_to_size(size, val);
+	if (!amount)
+		return val;
 	return (val << (bits - amount)) | (val >> amount);
 }
 

Original file line number	Diff line number	Diff line change
`@@ -489,6 +489,8 @@ static __uint128_t rotate(int size, __uint128_t val, int amount)`
`489`	`489`
`490`	`490`	`amount = (amount + bits) % bits;`
`491`	`491`	`val = cut_to_size(size, val);`
	`492`	`+ if (!amount)`
	`493`	`+ return val;`
`492`	`494`	`return (val << (bits - amount)) \| (val >> amount);`
`493`	`495`	`}`
`494`	`496`