linux-kernel - [PATCH v2] KVM: s390: selftest: memop: Fix undefined behavior

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Message-Id: <20240111094805.363047-1-nsg@linux.ibm.com>
Date: Thu, 11 Jan 2024 10:48:05 +0100
From: Nina Schoetterl-Glausch <nsg@...ux.ibm.com>
To: Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>
Cc: Nina Schoetterl-Glausch <nsg@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
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 <nsg@...ux.ibm.com>
---

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