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Tue, 1 Sep 2026 07:38:48 +0000 (GMT) Date: Tue, 1 Sep 2026 09:38:59 +0200 From: Steffen Eiden To: Karl Mehltretter Cc: Marc Zyngier , Oliver Upton , kvmarm@lists.linux.dev, Fuad Tabba , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Mark Rutland , Paolo Bonzini , Sean Christopherson , Shuah Khan , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH 1/2] KVM: arm64: Return -EINVAL for an empty SMCCC filter range at base 0 Message-ID: <20260901073859.185345-A-seiden@linux.ibm.com> References: <20260829054856.70549-1-kmehltretter@gmail.com> <20260829054856.70549-2-kmehltretter@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260829054856.70549-2-kmehltretter@gmail.com> X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: ZCbQ-ZklX7stda1AuCkPQ0Djjt_a0WKY X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTAxMDA2NiBTYWx0ZWRfX4h+TXCOEI7wH 6eMfhCl9yIVObK3BCrNHD8Dq3qA3ZMS/VYvCRHiJftV4ivux8cMKSQfM92VTBM9XfXw3PmxqFNh 9OTN9SgrFiyzSNKVKBmZQwyaJEU1aJmlrNpYpjbcYTC+RtkDGKeVc9YQb9alJ3jlq/OhHgov1uV JX30A0+5iKSHW0PB6rGEkJGZTI/7vGzNAVe3pr31cENAs+mjp9eQ6qUEJ9EV3ezAHEB79sQ58Y9 nJ5YwZGiqaGAWTxYGyWT6R9F6OKuMB9e0fnyZMIEbtUjBbV8UoTAPDcecO6siPiNJ9gBLHbFoDs O7vd0JCz9y8jF5x+LHatF7wO03UuBCd2SnD7m6JEV5zYZD82drlk8SZD8sPtMcGJteuByBxvocw vIArUz59EW6PIbbEWkY4nWUN6wdufOT1SrLKPZWhZx1odnRqyito0KZSb+SkDigDpDaCZsUgAYX WMfgJ6x3bko8mOt7fuw== X-Authority-Analysis: v=2.4 cv=Osl/DS/t c=1 sm=1 tr=0 ts=6a96810c cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=kj9zAlcOel0A:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=pGLkceISAAAA:8 a=VnNF1IyMAAAA:8 a=sTVcf0stEawvOQYPuTgA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTAxMDA2NiBTYWx0ZWRfXy4lZ/J7YpckL K0SY6MkUpi5sUw7oztTXtF2gTI3R/neK7rxtxiz60RLfyOvT9Nf0r+CbEwZfrLb399CxCRuQ3Y3 sM+IqxmBNeFFM3kYX5eDNYok2nAILFA= X-Proofpoint-ORIG-GUID: GL9tonZEYnwAQvDdc17GjcJN60W2-KOG X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-01_02,2026-08-31_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 malwarescore=0 suspectscore=0 bulkscore=0 lowpriorityscore=0 adultscore=0 impostorscore=0 phishscore=0 clxscore=1011 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609010066 On Sat, Aug 29, 2026 at 07:48:55AM +0200, Karl Mehltretter wrote: > kvm_smccc_set_filter() only rejects a range if its inclusive end, > base + nr_functions - 1, is below base. That catches an empty range > (nr_functions == 0) at every nonzero base, but at base 0 the end wraps > to U32_MAX and KVM tries to insert [0, U32_MAX], which overlaps the > reserved Arm Architecture Calls ranges. KVM_ARM_VM_SMCCC_FILTER then > returns -EEXIST instead of the -EINVAL that the smccc_filter selftest > expects for an empty range. > > Reject a zero function count explicitly. > > Tested with a userspace reproducer on an arm64 VHE host under QEMU TCG: > EEXIST before, EINVAL after. > > Fixes: 821d935c87bc ("KVM: arm64: Introduce support for userspace SMCCC filtering") > Assisted-by: LLM > Signed-off-by: Karl Mehltretter Good catch. Reviewed-by: Steffen Eiden FWIW: Tested it on my downstream version of arm-on-s390 with hypercalls already implemented.