2024-01-11 09:48:40

by Nina Schoetterl-Glausch

Subject: [PATCH v2] KVM: s390: selftest: memop: Fix undefined behavior

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: 0dd714bfd200 ("KVM: s390: selftest: memop: Add cmpxchg tests")
Signed-off-by: Nina Schoetterl-Glausch <[email protected]>
---

v1 -> v2:
use early return instead of modulus

tools/testing/selftests/kvm/s390x/memop.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/kvm/s390x/memop.c b/tools/testing/selftests/kvm/s390x/memop.c
index bb3ca9a5d731..4ec8d0181e8d 100644
--- 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);
}


base-commit: 305230142ae0637213bf6e04f6d9f10bbcb74af8
--
2.40.1

2024-02-22 11:34:41

by Janosch Frank

Subject: Re: [PATCH v2] KVM: s390: selftest: memop: Fix undefined behavior

On 1/11/24 10:48, Nina Schoetterl-Glausch wrote:
> 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: 0dd714bfd200 ("KVM: s390: selftest: memop: Add cmpxchg tests")
> Signed-off-by: Nina Schoetterl-Glausch <[email protected]>


Acked-by: Janosch Frank <[email protected]>