From 7af7cfbe78e23af0ac3cbe9b2b16da69f1412222 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <maz@kernel.org>
Date: Tue, 29 Apr 2025 12:41:16 +0100
Subject: [PATCH] KVM: arm64: Prevent userspace from disabling AArch64 support
at any virtualisable EL
A sorry excuse for a selftest is trying to disable AArch64 support.
And yes, this goes as well as you can imagine.
Let's forbid this sort of things. Normal userspace shouldn't get
caught doing that.
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com>
Link: https://lore.kernel.org/r/20250429114117.3618800-2-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
arch/arm64/kvm/sys_regs.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 005ad28f7306..5dde9285afc8 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1945,6 +1945,12 @@ static int set_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
if ((hw_val & mpam_mask) == (user_val & mpam_mask))
user_val &= ~ID_AA64PFR0_EL1_MPAM_MASK;
+ /* Fail the guest's request to disable the AA64 ISA at EL{0,1,2} */
+ if (!FIELD_GET(ID_AA64PFR0_EL1_EL0, user_val) ||
+ !FIELD_GET(ID_AA64PFR0_EL1_EL1, user_val) ||
+ (vcpu_has_nv(vcpu) && !FIELD_GET(ID_AA64PFR0_EL1_EL2, user_val)))
+ return -EINVAL;
+
return set_id_reg(vcpu, rd, user_val);
}