From nobody Fri Sep 25 08:45:59 2026 Received: from mta0.migadu.com (out-118.mta0.migadu.com [91.218.175.118]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7D92844F550 for ; Tue, 15 Sep 2026 07:04:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.118 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789455869; cv=none; b=t9FqmXKwVTGhRaxalsIVWG4z3A4bFSThP8dhnRleJt+pfHZNCyX4lLL3Q+uKxETUlJtxE4HWfKuw2d8VdfDSk0Pqnh0b56patHSLwtIfMOTzkZApG7AQG4V4ho2nn+UszEikptNvr7AsnsdojROml+TDvgbV2ZWUlwOU6N6J1KE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789455869; c=relaxed/simple; bh=ANhxith82ULbv0/JaaJ8goUq0CxV3cuc4rjj5cuj3dU=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=UgoiRCkMGDIo5zuEB4PFwRw2Bw3OTeWwMz4XYmhtWDUmJ9ZnHolOIJgLR/VLwTQZTIa3LfddD/QTZM1GKDCMZKQuBfQ2tPXlI2TTXdJ+InHal09bnpk20vb0EQCLnsmY4npb5a5JKtCO1+ILF0zxNvF1ocpsOtxSuwIpxJzcVx8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=p46XEyyi; arc=none smtp.client-ip=91.218.175.118 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="p46XEyyi" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=ANhxith82ULbv0/JaaJ8goUq0CxV3cuc4rjj5cuj3dU=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1789455863; v=1; x=1790060663; b=p46XEyyi5VK6kYdJNj6dDh+yAg5PJ6zeWbO/NVYhYLMF4N41z2k4ANoHJzNnAdb1YNwH/1kz b/SpP/9onmTjkXf+PWhvslgIfxrgojUi4sbibhICmwlRT2UzDeTdXX4D/PYanWM7Mt3GKAMSJab H7e5yq0GgGvc7J/vMWuaurlo= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 43fcf61e14ba3efe; Tue, 15 Sep 2026 07:04:23 +0000 X-Mizu-Trace-ID: 43fcf61e14ba3efe X-Migadu-Flow: FLOW_OUT From: Fuad Tabba To: maz@kernel.org, oupton@kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: catalin.marinas@arm.com, will@kernel.org, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, mark.rutland@arm.com, steven.price@arm.com, vdonnefort@google.com, qperret@google.com, tabba@google.com Subject: [PATCH v2 1/2] KVM: arm64: Validate the host vCPU's VM before reading it under pKVM Date: Tue, 15 Sep 2026 08:04:17 +0100 Message-Id: <20260915070418.3209779-2-fuad.tabba@linux.dev> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20260915070418.3209779-1-fuad.tabba@linux.dev> References: <20260915070418.3209779-1-fuad.tabba@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" On an MTE-capable host under pKVM, enter_exception64() reads the VM's MTE flag through vcpu->kvm, which for a host vCPU is a host-writable pointer nothing validates. The host can point it at any address in the hyp linear map and read back bit 1 of that word through PSR_TCO in the vCPU's CPSR, or panic the hypervisor with an unmapped one. Get the VM through a get/put pair around the read: a loaded vCPU's is the hyp VM, an unloaded host vCPU's is read once and pinned, and a pointer the host never shared leaves TCO clear. Fixes: ea7fc1bb1cd1b ("KVM: arm64: Introduce MTE VM feature") Reported-by: Sashiko Closes: https://lore.kernel.org/all/20260914070536.877D91F000FF@smtp.kernel= .org/ Cc: stable@vger.kernel.org Signed-off-by: Fuad Tabba Reviewed-by: Joey Gouly Reviewed-by: Vincent Donnefort --- arch/arm64/kvm/hyp/exception.c | 5 ++- arch/arm64/kvm/hyp/include/hyp/adjust_pc.h | 18 ++++++++++ arch/arm64/kvm/hyp/nvhe/pkvm.c | 39 ++++++++++++++++++++++ 3 files changed, 61 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c index 754e2dc1df54a..6e60d890afa4a 100644 --- a/arch/arm64/kvm/hyp/exception.c +++ b/arch/arm64/kvm/hyp/exception.c @@ -70,6 +70,7 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsi= gned long target_mode, enum exception_type type) { unsigned long sctlr, vbar, old, new, mode; + struct kvm *kvm; u64 exc_offset; =20 mode =3D *vcpu_cpsr(vcpu) & (PSR_MODE_MASK | PSR_MODE32_BIT); @@ -109,8 +110,10 @@ static void enter_exception64(struct kvm_vcpu *vcpu, u= nsigned long target_mode, new |=3D (old & PSR_C_BIT); new |=3D (old & PSR_V_BIT); =20 - if (kvm_has_mte(kern_hyp_va(vcpu->kvm))) + kvm =3D vcpu_get_kvm(vcpu); + if (kvm && kvm_has_mte(kvm)) new |=3D PSR_TCO_BIT; + vcpu_put_kvm(vcpu, kvm); =20 new |=3D (old & PSR_DIT_BIT); =20 diff --git a/arch/arm64/kvm/hyp/include/hyp/adjust_pc.h b/arch/arm64/kvm/hy= p/include/hyp/adjust_pc.h index 4fdfeabefeb43..a4fb04faa7d09 100644 --- a/arch/arm64/kvm/hyp/include/hyp/adjust_pc.h +++ b/arch/arm64/kvm/hyp/include/hyp/adjust_pc.h @@ -13,6 +13,24 @@ #include #include =20 +/* + * Under pKVM a host vCPU's ->kvm is host-writable: the nVHE pair + * validates it. + */ +#ifdef __KVM_NVHE_HYPERVISOR__ +struct kvm *vcpu_get_kvm(struct kvm_vcpu *vcpu); +void vcpu_put_kvm(struct kvm_vcpu *vcpu, struct kvm *kvm); +#else +static inline struct kvm *vcpu_get_kvm(struct kvm_vcpu *vcpu) +{ + return vcpu->kvm; +} + +static inline void vcpu_put_kvm(struct kvm_vcpu *vcpu, struct kvm *kvm) +{ +} +#endif + static inline void kvm_skip_instr(struct kvm_vcpu *vcpu) { if (vcpu_mode_is_32bit(vcpu)) { diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c index 459bd9eb7e4bc..9bdc7a9b84b8c 100644 --- a/arch/arm64/kvm/hyp/nvhe/pkvm.c +++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c @@ -11,6 +11,8 @@ =20 #include =20 +#include + #include #include #include @@ -304,6 +306,43 @@ struct pkvm_hyp_vcpu *pkvm_get_loaded_hyp_vcpu(void) =20 } =20 +static struct pkvm_hyp_vm *loaded_hyp_vm_of(struct kvm_vcpu *vcpu) +{ + struct pkvm_hyp_vcpu *hyp_vcpu =3D pkvm_get_loaded_hyp_vcpu(); + + if (hyp_vcpu && + (vcpu =3D=3D &hyp_vcpu->vcpu || vcpu =3D=3D hyp_vcpu->host_vcpu)) + return pkvm_hyp_vcpu_to_hyp_vm(hyp_vcpu); + + return NULL; +} + +/* An unloaded host vCPU's VM is mapped at EL2 only while pinned. */ +struct kvm *vcpu_get_kvm(struct kvm_vcpu *vcpu) +{ + struct pkvm_hyp_vm *hyp_vm; + struct kvm *kvm; + + if (!is_protected_kvm_enabled()) + return kern_hyp_va(vcpu->kvm); + + hyp_vm =3D loaded_hyp_vm_of(vcpu); + if (hyp_vm) + return &hyp_vm->kvm; + + kvm =3D kern_hyp_va(READ_ONCE(vcpu->kvm)); + if (hyp_pin_shared_mem(kvm, kvm + 1)) + return NULL; + + return kvm; +} + +void vcpu_put_kvm(struct kvm_vcpu *vcpu, struct kvm *kvm) +{ + if (kvm && is_protected_kvm_enabled() && !loaded_hyp_vm_of(vcpu)) + hyp_unpin_shared_mem(kvm, kvm + 1); +} + struct pkvm_hyp_vm *get_pkvm_hyp_vm(pkvm_handle_t handle) { struct pkvm_hyp_vm *hyp_vm; --=20 2.39.5 From nobody Fri Sep 25 08:45:59 2026 Received: from mta0.migadu.com (out-128.mta0.migadu.com [91.218.175.128]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D37D444BCB5 for ; 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arc=none smtp.client-ip=91.218.175.128 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="RfYBmcS7" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=TxjB2nuw/omS0r1HuiWJ8ceXglPNuUd+88Xw3+fRY0o=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1789455864; v=1; x=1790060664; b=RfYBmcS79BbKA5YbpkzRHGNMsCdzXRD1HEpL6hdNfl/pGiDHfUrufUgaKXXUPH/IHYRiBT23 Iwz3Kn12AcPNbXgE1yV2U/XRabVttCjM3d7gNYu+FqlFKxra+ZQ9ca17ZnyJup/oUvuH3mDdPBQ Ode+nbxhx5VGh0EOwRXLWuoA= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id d9900a21abb41ef0; Tue, 15 Sep 2026 07:04:24 +0000 X-Mizu-Trace-ID: d9900a21abb41ef0 X-Migadu-Flow: FLOW_OUT From: Fuad Tabba To: maz@kernel.org, oupton@kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: catalin.marinas@arm.com, will@kernel.org, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, mark.rutland@arm.com, steven.price@arm.com, vdonnefort@google.com, qperret@google.com, tabba@google.com Subject: [PATCH v2 2/2] KVM: arm64: Pin the host vCPU before adjusting its PC under pKVM Date: Tue, 15 Sep 2026 08:04:18 +0100 Message-Id: <20260915070418.3209779-3-fuad.tabba@linux.dev> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20260915070418.3209779-1-fuad.tabba@linux.dev> References: <20260915070418.3209779-1-fuad.tabba@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Under pKVM, a page the host shares with EL2 is mapped at EL2 only while it's pinned, and the host vCPU is pinned at its first KVM_RUN. KVM_SET_VCPU_EVENTS with ext_dabt_pending reaches __kvm_adjust_pc() at EL2 before that, and dereferencing the unmapped host vCPU panics the hypervisor. Any process holding /dev/kvm on a pKVM host can trigger it. Pin the host vCPU around the adjustment when no hyp vCPU is loaded for it. A loaded hyp vCPU implies it's pinned. A pin fails only for memory the host never shared, and the request is then dropped like any other bad host pointer. Fixes: efa1368ba9f4b ("KVM: arm64: Commit exceptions from KVM_SET_VCPU_EVEN= TS immediately") Cc: stable@vger.kernel.org Signed-off-by: Fuad Tabba Reviewed-by: Joey Gouly Reviewed-by: Vincent Donnefort --- arch/arm64/kvm/hyp/nvhe/hyp-main.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/h= yp-main.c index 9a3b92e626adb..4cb7347db2514 100644 --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c @@ -542,8 +542,25 @@ static void handle___pkvm_host_mkyoung_guest(struct kv= m_cpu_context *host_ctxt) static void handle___kvm_adjust_pc(struct kvm_cpu_context *host_ctxt) { DECLARE_REG(struct kvm_vcpu *, vcpu, host_ctxt, 1); + struct pkvm_hyp_vcpu *hyp_vcpu; + struct kvm_vcpu *host_vcpu; =20 - __kvm_adjust_pc(kern_hyp_va(vcpu)); + host_vcpu =3D __get_host_hyp_vcpus(vcpu, &hyp_vcpu); + if (host_vcpu) { + __kvm_adjust_pc(host_vcpu); + return; + } + + /* + * With no hyp vCPU loaded for it, the host vCPU may be unpinned, + * and so unmapped at EL2: its first run pins it. + */ + host_vcpu =3D kern_hyp_va(vcpu); + if (hyp_pin_shared_mem(host_vcpu, host_vcpu + 1)) + return; + + __kvm_adjust_pc(host_vcpu); + hyp_unpin_shared_mem(host_vcpu, host_vcpu + 1); } =20 static void handle___kvm_flush_vm_context(struct kvm_cpu_context *host_ctx= t) --=20 2.39.5