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Tsirkin" , Paolo Bonzini , Richard Henderson , qemu-devel@nongnu.org Subject: [PATCH] hw/i386/amd_iommu: Avoid undefined behavior in amdvi_setevent_bits() Date: Fri, 31 Jul 2026 16:02:29 +0200 Message-ID: <20260731140229.259272-1-thuth@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.129.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -2 X-Spam_score: -0.3 X-Spam_bar: / X-Spam_report: (-0.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.58, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: Thomas Huth The code in amdvi_encode_event() calls amdvi_setevent_bits() with start = 64: amdvi_setevent_bits(evt, addr, 64, 64); and amdvi_setevent_bits() then calculates: uint64_t mask = MAKE_64BIT_MASK(start, length); but this MAKE_64BIT_MASK() macro shifts a value left by "start" bit positions. Shifting left by more than 63 is undefined behavior and could have unexpected results with different compilers / architectures. Fix it by using "bitpos" instead, which was likely the original intended behavior anyway. (bitpos is calculated as bitpos = start % 64). Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3633 Signed-off-by: Thomas Huth --- hw/i386/amd_iommu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c index 90252c52af4..578c27ccbef 100644 --- a/hw/i386/amd_iommu.c +++ b/hw/i386/amd_iommu.c @@ -323,7 +323,7 @@ static void amdvi_setevent_bits(uint64_t *buffer, uint64_t value, int start, int length) { int index = start / 64, bitpos = start % 64; - uint64_t mask = MAKE_64BIT_MASK(start, length); + uint64_t mask = MAKE_64BIT_MASK(bitpos, length); buffer[index] &= ~mask; buffer[index] |= (value << bitpos) & mask; } -- 2.55.0