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AJvYcCWzlXIR6HKr3frg7/KJIjEzEP5emVUkZYQUz+AansRBzWUSUfinXkm62j21nenXRO70VjStpsSMZAZ+BgU=@vger.kernel.org X-Gm-Message-State: AOJu0YzGpurNTUXZJbD0ds98BwQg5we5zixrhJLzn6pr9ZYfTEgAfYh0 vYM5zzS8Ik9dzahQWIRo0+7V+NrA/Mb7vWvBnbp9VCsddVxiwqGgNVzYkCd+bAUHjm7UlvNQ+nz S/Q== X-Google-Smtp-Source: AGHT+IG0rnfQOBcsGBc89nGQ7P5SqEhx394iLm0A9p+JH2UauaQ7PKGIBjoXKOQU6ONzPdt2vT+TuR01CA== X-Received: from ejdcu3.prod.google.com ([2002:a17:906:ba83:b0:b73:2695:dbc5]) (user=ptosi job=prod-delivery.src-stubby-dispatcher) by 2002:a17:907:6d13:b0:b77:18a0:3c8b with SMTP id a640c23a62f3a-b7718a03cd2mr1308264966b.1.1764613196560; Mon, 01 Dec 2025 10:19:56 -0800 (PST) Date: Mon, 01 Dec 2025 18:19:52 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-B4-Tracking: v=1; b=H4sIAEjcLWkC/x3MQQqAIBBA0avIrBN0QpCuEi1KxxooC40IxLsnL d/i/wKZElOGQRRI9HDmMzboToDb5riSZN8MqNBoVFrmwzknA+83JWms9T5oXHpjoCVXosDvvxu nWj8ivT43XgAAAA== X-Change-Id: 20251201-smccc-filter-588ddf12b355 X-Mailer: b4 0.14.2 Message-ID: <20251201-smccc-filter-v1-1-b4831416f8a3@google.com> Subject: [PATCH] KVM: arm64: Prevent FWD_TO_USER of SMCCC to pKVM From: "=?utf-8?q?Pierre-Cl=C3=A9ment_Tosi?=" To: kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev Cc: Joey Gouly , Marc Zyngier , Oliver Upton , Suzuki K Poulose , Vincent Donnefort , Will Deacon , Zenghui Yu , "=?utf-8?q?Pierre-Cl=C3=A9ment_Tosi?=" Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable With protected VMs, forwarding guest HVC/SMCs happens at two interfaces: pKVM [EL2] <--> KVM [EL1] <--> VMM [EL0] so it might be possible for EL0 to successfully register with EL1 to handle guest SMCCC calls but never see the KVM_EXIT_HYPERCALL, even if the calls are properly issued by the guest, due to EL2 handling them so that (host) EL1 never gets a chance to exit to EL0. Instead, avoid that confusing situation and make userspace fail early by disallowing KVM_ARM_VM_SMCCC_FILTER-ing calls from protected guests in the KVM FID range (which pKVM re-uses). DEN0028 defines 65536 "Vendor Specific Hypervisor Service Calls": - the first ARM_SMCCC_KVM_NUM_FUNCS (128) can be custom-defined - the following 3 are currently standardized - the rest is "reserved for future expansion" so reserve them all, like commit 821d935c87bc ("KVM: arm64: Introduce support for userspace SMCCC filtering") with the Arm Architecture Calls. Alternatively, we could have only reserved the ARM_SMCCC_KVM_NUM_FUNCS (or even a subset of it) and the "Call UID Query" but that would have risked future conflicts between that uAPI and an extension of the SMCCC or of the pKVM ABI. Signed-off-by: Pierre-Cl=C3=A9ment Tosi --- Documentation/virt/kvm/devices/vm.rst | 11 ++++++++++ arch/arm64/kvm/hypercalls.c | 39 +++++++++++++++++++++++++++++++= ++++ 2 files changed, 50 insertions(+) diff --git a/Documentation/virt/kvm/devices/vm.rst b/Documentation/virt/kvm= /devices/vm.rst index a4d39fa1b0834b090318250db3b670b0b3174259..9ed4b7afe022023346d4835d33a= 901e557fc4765 100644 --- a/Documentation/virt/kvm/devices/vm.rst +++ b/Documentation/virt/kvm/devices/vm.rst @@ -400,3 +400,14 @@ will reject attempts to define a filter for any portio= n of these ranges: 0x8000_0000 0x8000_FFFF 0xC000_0000 0xC000_FFFF =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D + +Protected KVM (pKVM) reserves the 'Vendor Specific Hypervisor Service Call= s' +range of function IDs and will reject attempts to define a filter for any +portion of these ranges for a protected VM (``KVM_VM_TYPE_ARM_PROTECTED``): + + =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D + Start End (inclusive) + =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D + 0x8600_0000 0x8600_FFFF + 0xC600_0000 0xC600_FFFF + =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c index 58c5fe7d757274d9079606fcc378485980c6c0f8..5ddcdd70a6b280914048e7683da= fb778d0f24658 100644 --- a/arch/arm64/kvm/hypercalls.c +++ b/arch/arm64/kvm/hypercalls.c @@ -135,6 +135,21 @@ static bool kvm_smccc_test_fw_bmap(struct kvm_vcpu *vc= pu, u32 func_id) ARM_SMCCC_SMC_64, \ 0, ARM_SMCCC_FUNC_MASK) =20 +#define SMC32_VHYP_RANGE_BEGIN ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID +#define SMC32_VHYP_RANGE_END ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \ + ARM_SMCCC_SMC_32, \ + ARM_SMCCC_OWNER_VENDOR_HYP, \ + ARM_SMCCC_FUNC_MASK) + +#define SMC64_VHYP_RANGE_BEGIN ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \ + ARM_SMCCC_SMC_64, \ + ARM_SMCCC_OWNER_VENDOR_HYP, \ + 0) +#define SMC64_VHYP_RANGE_END ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \ + ARM_SMCCC_SMC_64, \ + ARM_SMCCC_OWNER_VENDOR_HYP, \ + ARM_SMCCC_FUNC_MASK) + static int kvm_smccc_filter_insert_reserved(struct kvm *kvm) { int r; @@ -158,6 +173,30 @@ static int kvm_smccc_filter_insert_reserved(struct kvm= *kvm) if (r) goto out_destroy; =20 + /* + * Prevent userspace from registering to handle any SMCCC call in the + * vendor hypervisor range for pVMs, avoiding the confusion of guest + * calls seemingly not resulting in KVM_RUN exits because pKVM handles + * them without ever returning to the host. This is NOT for security. + */ + if (kvm_vm_is_protected(kvm)) { + r =3D mtree_insert_range(&kvm->arch.smccc_filter, + SMC32_VHYP_RANGE_BEGIN, + SMC32_VHYP_RANGE_END, + xa_mk_value(KVM_SMCCC_FILTER_HANDLE), + GFP_KERNEL_ACCOUNT); + if (r) + goto out_destroy; + + r =3D mtree_insert_range(&kvm->arch.smccc_filter, + SMC64_VHYP_RANGE_BEGIN, + SMC64_VHYP_RANGE_END, + xa_mk_value(KVM_SMCCC_FILTER_HANDLE), + GFP_KERNEL_ACCOUNT); + if (r) + goto out_destroy; + } + return 0; out_destroy: mtree_destroy(&kvm->arch.smccc_filter); --- base-commit: 7d0a66e4bb9081d75c82ec4957c50034cb0ea449 change-id: 20251201-smccc-filter-588ddf12b355 Best regards, --=20 Pierre-Cl=C3=A9ment Tosi