[PATCH v2 23/43] KVM: arm64: Validate register access for a Realm VM

Steven Price
2024-04-12T08:44:12Z

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@arm.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 e2f762d959bb..a035689dc39b 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -782,12 +782,38 @@ 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, except for a few configuration fields that correspond to
+ * Realm parameters.
+ */
+static bool validate_realm_set_reg(struct kvm_vcpu *vcpu,
+ const struct kvm_one_reg *reg)
+{
+ if ((reg->id & KVM_REG_ARM_COPROC_MASK) == KVM_REG_ARM_CORE) {
+ u64 off = core_reg_offset_from_id(reg->id);
+
+ 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