[PATCH] KVM: arm64: Sync SCTLR_EL1 before a pVM's CPU_ON reads its endianness

[PATCH] KVM: arm64: Sync SCTLR_EL1 before a pVM's CPU_ON reads its endianness

[Fuad Tabba]

pKVM handles a protected guest's PSCI CPU_ON at EL2 before the guest's
EL1 sysregs are saved, so kvm_vcpu_is_be() reads a stale SCTLR_EL1. A
guest that changes SCTLR_EL1.EE and calls CPU_ON before its next exit
to the host starts the target vCPU with the old endianness.

Sync SCTLR_EL1 before the read, as inject_sync64() does.

Fixes: 9d4ec80be2eb4 ("KVM: arm64: Handle PSCI calls for protected VMs at EL2")
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---

Notes:
    inject_sync64() is the only other reader on a protected guest's exit
    path of a guest-writable EL1 sysreg's copy, and it syncs that register
    first. Saving SCTLR_EL1 before the in-loop exit handlers instead would
    put the save on every protected exit for two readers. A non-protected
    guest's CPU_ON is handled by the host, after the sysregs are saved.

 arch/arm64/kvm/hyp/nvhe/pkvm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index fc0475f0877d1..e421f45383e0d 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -1321,6 +1321,9 @@ static bool pvm_psci_vcpu_on(struct pkvm_hyp_vcpu *hyp_vcpu)
 		goto error;
 	}
 
+	/* Sync SCTLR_EL1 for kvm_vcpu_is_be(), as HVCs are handled before sysregs are resync'ed. */
+	__vcpu_assign_sys_reg(&hyp_vcpu->vcpu, SCTLR_EL1, read_sysreg_el1(SYS_SCTLR));
+
 	reset_state = &target->vcpu.arch.reset_state;
 	WRITE_ONCE(reset_state->pc, smccc_get_arg2(&hyp_vcpu->vcpu));
 	WRITE_ONCE(reset_state->r0, smccc_get_arg3(&hyp_vcpu->vcpu));

base-commit: 7475ea8b58616b33c04afb976cf0fbaad9dd63fb
-- 
2.47.3