arm64: KVM: Prevent speculative S1 PTW when restoring vcpu context

When handling erratum 1319367, we must ensure that the page table
walker cannot parse the S1 page tables while the guest is in an
inconsistent state. This is done as follows:

On guest entry:
- TCR_EL1.EPD{0,1} are set, ensuring that no PTW can occur
- all system registers are restored, except for TCR_EL1 and SCTLR_EL1
- stage-2 is restored
- SCTLR_EL1 and TCR_EL1 are restored

On guest exit:
- SCTLR_EL1.M and TCR_EL1.EPD{0,1} are set, ensuring that no PTW can occur
- stage-2 is disabled
- All host system registers are restored

Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

1 files changed, 33 insertions, 2 deletions

diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
index 7ddbc849b580..22b8128d19f6 100644
--- a/arch/arm64/kvm/hyp/sysreg-sr.c
+++ b/arch/arm64/kvm/hyp/sysreg-sr.c
@@ -117,12 +117,26 @@ static void __hyp_text __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt)
 {
 	write_sysreg(ctxt->sys_regs[MPIDR_EL1],		vmpidr_el2);
 	write_sysreg(ctxt->sys_regs[CSSELR_EL1],	csselr_el1);
-	write_sysreg_el1(ctxt->sys_regs[SCTLR_EL1],	SYS_SCTLR);
+
+	if (!cpus_have_const_cap(ARM64_WORKAROUND_1319367)) {
+		write_sysreg_el1(ctxt->sys_regs[SCTLR_EL1],	SYS_SCTLR);
+		write_sysreg_el1(ctxt->sys_regs[TCR_EL1],	SYS_TCR);
+	} else	if (!ctxt->__hyp_running_vcpu) {
+		/*
+		 * Must only be done for guest registers, hence the context
+		 * test. We're coming from the host, so SCTLR.M is already
+		 * set. Pairs with __activate_traps_nvhe().
+		 */
+		write_sysreg_el1((ctxt->sys_regs[TCR_EL1] |
+				  TCR_EPD1_MASK | TCR_EPD0_MASK),
+				 SYS_TCR);
+		isb();
+	}
+
 	write_sysreg(ctxt->sys_regs[ACTLR_EL1],		actlr_el1);
 	write_sysreg_el1(ctxt->sys_regs[CPACR_EL1],	SYS_CPACR);
 	write_sysreg_el1(ctxt->sys_regs[TTBR0_EL1],	SYS_TTBR0);
 	write_sysreg_el1(ctxt->sys_regs[TTBR1_EL1],	SYS_TTBR1);
-	write_sysreg_el1(ctxt->sys_regs[TCR_EL1],	SYS_TCR);
 	write_sysreg_el1(ctxt->sys_regs[ESR_EL1],	SYS_ESR);
 	write_sysreg_el1(ctxt->sys_regs[AFSR0_EL1],	SYS_AFSR0);
 	write_sysreg_el1(ctxt->sys_regs[AFSR1_EL1],	SYS_AFSR1);
@@ -135,6 +149,23 @@ static void __hyp_text __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt)
 	write_sysreg(ctxt->sys_regs[PAR_EL1],		par_el1);
 	write_sysreg(ctxt->sys_regs[TPIDR_EL1],		tpidr_el1);
 
+	if (cpus_have_const_cap(ARM64_WORKAROUND_1319367) &&
+	    ctxt->__hyp_running_vcpu) {
+		/*
+		 * Must only be done for host registers, hence the context
+		 * test. Pairs with __deactivate_traps_nvhe().
+		 */
+		isb();
+		/*
+		 * At this stage, and thanks to the above isb(), S2 is
+		 * deconfigured and disabled. We can now restore the host's
+		 * S1 configuration: SCTLR, and only then TCR.
+		 */
+		write_sysreg_el1(ctxt->sys_regs[SCTLR_EL1],	SYS_SCTLR);
+		isb();
+		write_sysreg_el1(ctxt->sys_regs[TCR_EL1],	SYS_TCR);
+	}
+
 	write_sysreg(ctxt->gp_regs.sp_el1,		sp_el1);
 	write_sysreg_el1(ctxt->gp_regs.elr_el1,		SYS_ELR);
 	write_sysreg_el1(ctxt->gp_regs.spsr[KVM_SPSR_EL1],SYS_SPSR);