From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-86.mta0.migadu.com [91.218.175.86]) (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 8EFE0403150 for ; Mon, 7 Sep 2026 07:01:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.86 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788764511; cv=none; b=tcauAqz+iAjBtB+wZUENpP2giG0J4BPbtiWck+dueB77Mt5JqZYRbtU7GOovv3SWiVe/ZE2GsDjIOne2kAKLGqFVFznOAvfayWxYwhOjgo/vwnHbyF1QCAi2CVtRbi4YaygY8P6H/fMgI1mCuQ5HtHoBWDaqtlznHm/C9KaEAFg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788764511; c=relaxed/simple; bh=K+Cw1Rhs/pIXecXIjGAEGbyJhwCxhPQM371NHFscWfw=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=pC5WvHlkBYu8JuAa8hmeF+QPHVUDqxNsJOrSHpp4EmHigdZZhjodKaRXYwomhHhHzhjZ2rw7GjfP+XmXLUxtO6KpZuSgIa64UbpB23Y7mRsz24UD6ISmptSIAiY+ND1VEh/Np0O1dwxuKmMQPBUx8okzsbv7RL1n6h6PLAG/6So= 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=p8fNQnYu; arc=none smtp.client-ip=91.218.175.86 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="p8fNQnYu" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=K+Cw1Rhs/pIXecXIjGAEGbyJhwCxhPQM371NHFscWfw=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788764502; v=1; x=1789369302; b=p8fNQnYuVsFPhdAhPxr5iNDsAmcuAMoCKemaon+6vgdDeWzMd3SgfbLHHsReo1SazQqmPFUQ G6XsECqPrraRiSH+Ev8xUFHy6VOLDQKqyKiNvee3gKb8rAj9gBLGnabzf3t75eh0xftsbSURpzd a3tahqUpAkalCaOFzIan1hyA= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id d6bcb7f9e1bd0ff6; Mon, 07 Sep 2026 07:01:42 +0000 X-Mizu-Trace-ID: d6bcb7f9e1bd0ff6 X-Migadu-Flow: FLOW_OUT From: Fuad Tabba To: Marc Zyngier , Oliver Upton , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: Catalin Marinas , Will Deacon , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Vincent Donnefort , Quentin Perret , Fuad Tabba Subject: [PATCH v2 14/17] KVM: arm64: Reject host access to protected VM private state Date: Mon, 7 Sep 2026 07:59:59 +0100 Message-Id: <20260907070002.3333525-15-fuad.tabba@linux.dev> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20260907070002.3333525-1-fuad.tabba@linux.dev> References: <20260907070002.3333525-1-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: 8bit A protected vCPU's register and debug state is no longer exposed to the host. Host ioctls that would reach that state now fail rather than operate on a copy that is not the guest's: - KVM_GET_ONE_REG and KVM_SET_ONE_REG return -EPERM once the vCPU has run: the copy then holds reset values plus what the exit handlers marshal out. Pre-run access still builds the guest's boot state. - KVM_ARM_VCPU_INIT returns -EPERM once the vCPU has run: it would reset the host copy alone and rewrite mp_state, which EL2 reads only at hyp vCPU creation, so a vCPU the guest powered off would come back RUNNABLE. - KVM_SET_VCPU_EVENTS rejects external-abort injection with -EPERM; SError injection is forwarded and stays permitted. - KVM_SET_GUEST_DEBUG returns -EPERM: a protected guest's debug state is hypervisor-owned. Signed-off-by: Fuad Tabba --- arch/arm64/kvm/arm.c | 7 +++++++ arch/arm64/kvm/guest.c | 19 +++++++++++++++++++ 2 files changed, 26 insertions(+) diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 5c2587da815ab..37a260b139795 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -1750,6 +1750,13 @@ static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu, bool power_off = false; int ret; + /* + * Re-init would reset the host copy alone and rewrite mp_state + * after EL2 has read it. Pre-run init stays allowed. + */ + if (vcpu_is_protected(vcpu) && vcpu_has_run_once(vcpu)) + return -EPERM; + /* * Treat the power-off vCPU feature as ephemeral. Clear the bit to avoid * reflecting it in the finalized feature set, thus limiting its scope diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c index ab659795d4b2f..abab580a659d4 100644 --- a/arch/arm64/kvm/guest.c +++ b/arch/arm64/kvm/guest.c @@ -701,6 +701,10 @@ int kvm_arm_copy_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices) int kvm_arm_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg) { + /* Once the vCPU has run, the host copy is not the guest's state. */ + if (vcpu_is_protected(vcpu) && vcpu_has_run_once(vcpu)) + return -EPERM; + /* We currently use nothing arch-specific in upper 32 bits */ if ((reg->id & ~KVM_REG_SIZE_MASK) >> 32 != KVM_REG_ARM64 >> 32) return -EINVAL; @@ -718,6 +722,10 @@ int kvm_arm_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg) int kvm_arm_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg) { + /* Writes build the boot state; once run, EL2 owns the registers. */ + if (vcpu_is_protected(vcpu) && vcpu_has_run_once(vcpu)) + return -EPERM; + /* We currently use nothing arch-specific in upper 32 bits */ if ((reg->id & ~KVM_REG_SIZE_MASK) >> 32 != KVM_REG_ARM64 >> 32) return -EINVAL; @@ -786,6 +794,13 @@ int __kvm_arm_vcpu_set_events(struct kvm_vcpu *vcpu, u64 esr = events->exception.serror_esr; int ret = 0; + /* + * EL2 injects an external abort only to complete a forwarded abort. + * SError injection is forwarded. + */ + if (vcpu_is_protected(vcpu) && ext_dabt_pending) + return -EPERM; + /* * Immediately commit the pending SEA to the vCPU's architectural * state which is necessary since we do not return a pending SEA @@ -883,6 +898,10 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu, { trace_kvm_set_guest_debug(vcpu, dbg->control); + /* A protected guest's debug state is not exposed to the host. */ + if (vcpu_is_protected(vcpu)) + return -EPERM; + if (dbg->control & ~KVM_GUESTDBG_VALID_MASK) return -EINVAL; -- 2.39.5