linux-kernel - [RFC PATCH 19/28] KVM: arm64: Validate register access for a Realm VM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20230127112932.38045-20-steven.price@arm.com>
Date:   Fri, 27 Jan 2023 11:29:23 +0000
From:   Steven Price <steven.price@....com>
To:     kvm@...r.kernel.org, kvmarm@...ts.linux.dev
Cc:     Steven Price <steven.price@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        James Morse <james.morse@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Joey Gouly <joey.gouly@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Christoffer Dall <christoffer.dall@....com>,
        Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev
Subject: [RFC PATCH 19/28] KVM: arm64: Validate register access for a Realm VM

The RMM only allows setting the lower GPRS (x0-x7) and PC for a realm
guest. Check this in kvm_arm_set_reg() so that the VMM can receive a
suitable error return if other registers are accessed.

Signed-off-by: Steven Price <steven.price@....com>
---
 arch/arm64/kvm/guest.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index 5626ddb540ce..93468bbfb50e 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -768,12 +768,38 @@ int kvm_arm_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 	return kvm_arm_sys_reg_get_reg(vcpu, reg);
 }
 
+/*
+ * The RMI ABI only enables setting the lower GPRs (x0-x7) and PC.
+ * All other registers are reset to architectural or otherwise defined reset
+ * values by the RMM
+ */
+static bool validate_realm_set_reg(struct kvm_vcpu *vcpu,
+				   const struct kvm_one_reg *reg)
+{
+	u64 off = core_reg_offset_from_id(reg->id);
+
+	if ((reg->id & KVM_REG_ARM_COPROC_MASK) != KVM_REG_ARM_CORE)
+		return false;
+
+	switch (off) {
+	case KVM_REG_ARM_CORE_REG(regs.regs[0]) ...
+	     KVM_REG_ARM_CORE_REG(regs.regs[7]):
+	case KVM_REG_ARM_CORE_REG(regs.pc):
+		return true;
+	}
+
+	return false;
+}
+
 int kvm_arm_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 {
 	/* We currently use nothing arch-specific in upper 32 bits */
 	if ((reg->id & ~KVM_REG_SIZE_MASK) >> 32 != KVM_REG_ARM64 >> 32)
 		return -EINVAL;
 
+	if (kvm_is_realm(vcpu->kvm) && !validate_realm_set_reg(vcpu, reg))
+		return -EINVAL;
+
 	switch (reg->id & KVM_REG_ARM_COPROC_MASK) {
 	case KVM_REG_ARM_CORE:	return set_core_reg(vcpu, reg);
 	case KVM_REG_ARM_FW:
-- 
2.34.1