KVM: arm64: nVHE: Switch to hyp context for EL2

Save and restore the host context when switching to and from hyp. This
gives hyp its own context that the host will not see as a step towards a
full trust boundary between the two.

SP_EL0 and pointer authentication keys are currently shared between the
host and hyp so don't need to be switched yet.
Signed-off-by: Andrew Scull <ascull@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200915104643.2543892-13-ascull@google.com

arch/arm64/kvm/hyp/include/hyp/switch.h

@@ -372,6 +372,8 @@ static inline bool esr_is_ptrauth_trap(u32 esr)
 	ctxt_sys_reg(ctxt, key ## KEYHI_EL1) = __val;                   \
 } while(0)
 
+DECLARE_PER_CPU(struct kvm_cpu_context, kvm_hyp_ctxt);
+
 static inline bool __hyp_handle_ptrauth(struct kvm_vcpu *vcpu)
 {
 	struct kvm_cpu_context *ctxt;

arch/arm64/kvm/hyp/nvhe/Makefile

@@ -6,7 +6,7 @@
 asflags-y := -D__KVM_NVHE_HYPERVISOR__
 ccflags-y := -D__KVM_NVHE_HYPERVISOR__
 
-obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o
+obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o hyp-main.o
 obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
 	 ../fpsimd.o ../hyp-entry.o
 

arch/arm64/kvm/hyp/nvhe/host.S

@@ -12,6 +12,55 @@
 
 	.text
 
+SYM_FUNC_START(__host_exit)
+	stp	x0, x1, [sp, #-16]!
+
+	get_host_ctxt	x0, x1
+
+	ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN)
+
+	/* Store the host regs x2 and x3 */
+	stp	x2, x3,   [x0, #CPU_XREG_OFFSET(2)]
+
+	/* Retrieve the host regs x0-x1 from the stack */
+	ldp	x2, x3, [sp], #16	// x0, x1
+
+	/* Store the host regs x0-x1 and x4-x17 */
+	stp	x2, x3,   [x0, #CPU_XREG_OFFSET(0)]
+	stp	x4, x5,   [x0, #CPU_XREG_OFFSET(4)]
+	stp	x6, x7,   [x0, #CPU_XREG_OFFSET(6)]
+	stp	x8, x9,   [x0, #CPU_XREG_OFFSET(8)]
+	stp	x10, x11, [x0, #CPU_XREG_OFFSET(10)]
+	stp	x12, x13, [x0, #CPU_XREG_OFFSET(12)]
+	stp	x14, x15, [x0, #CPU_XREG_OFFSET(14)]
+	stp	x16, x17, [x0, #CPU_XREG_OFFSET(16)]
+
+	/* Store the host regs x18-x29, lr */
+	save_callee_saved_regs x0
+
+	/* Save the host context pointer in x29 across the function call */
+	mov	x29, x0
+	bl	handle_trap
+
+	/* Restore host regs x0-x17 */
+	ldp	x0, x1,   [x29, #CPU_XREG_OFFSET(0)]
+	ldp	x2, x3,   [x29, #CPU_XREG_OFFSET(2)]
+	ldp	x4, x5,   [x29, #CPU_XREG_OFFSET(4)]
+	ldp	x6, x7,   [x29, #CPU_XREG_OFFSET(6)]
+	ldp	x8, x9,   [x29, #CPU_XREG_OFFSET(8)]
+	ldp	x10, x11, [x29, #CPU_XREG_OFFSET(10)]
+	ldp	x12, x13, [x29, #CPU_XREG_OFFSET(12)]
+	ldp	x14, x15, [x29, #CPU_XREG_OFFSET(14)]
+	ldp	x16, x17, [x29, #CPU_XREG_OFFSET(16)]
+
+	/* Restore host regs x18-x29, lr */
+	restore_callee_saved_regs x29
+
+	/* Do not touch any register after this! */
+	eret
+	sb
+SYM_FUNC_END(__host_exit)
+
 SYM_FUNC_START(__hyp_do_panic)
 	mov	lr, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\
 		      PSR_MODE_EL1h)
@@ -34,7 +83,7 @@ SYM_FUNC_END(__hyp_do_panic)
 
 	/* Check for a stub HVC call */
 	cmp	x0, #HVC_STUB_HCALL_NR
-	b.hs	1f
+	b.hs	__host_exit
 
 	/*
 	 * Compute the idmap address of __kvm_handle_stub_hvc and
@@ -50,23 +99,6 @@ SYM_FUNC_END(__hyp_do_panic)
 	/* x5 = __pa(x5) */
 	sub	x5, x5, x6
 	br	x5
-
-1:
-	/*
-	 * Shuffle the parameters before calling the function
-	 * pointed to in x0. Assumes parameters in x[1,2,3].
-	 */
-	kern_hyp_va	x0
-	str	lr, [sp, #-16]!
-	mov	lr, x0
-	mov	x0, x1
-	mov	x1, x2
-	mov	x2, x3
-	blr	lr
-	ldr	lr, [sp], #16
-
-	eret
-	sb
 .L__vect_end\@:
 .if ((.L__vect_end\@ - .L__vect_start\@) > 0x80)
 	.error "host_el1_sync_vect larger than vector entry"

arch/arm64/kvm/hyp/nvhe/hyp-main.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 - Google Inc
+ * Author: Andrew Scull <ascull@google.com>
+ */
+
+#include <hyp/switch.h>
+
+#include <asm/kvm_asm.h>
+#include <asm/kvm_emulate.h>
+#include <asm/kvm_host.h>
+#include <asm/kvm_hyp.h>
+#include <asm/kvm_mmu.h>
+
+typedef unsigned long (*hypcall_fn_t)
+	(unsigned long, unsigned long, unsigned long);
+
+void handle_trap(struct kvm_cpu_context *host_ctxt)
+{
+	u64 esr = read_sysreg_el2(SYS_ESR);
+	hypcall_fn_t func;
+	unsigned long ret;
+
+	if (ESR_ELx_EC(esr) != ESR_ELx_EC_HVC64)
+		hyp_panic();
+
+	/*
+	 * __kvm_call_hyp takes a pointer in the host address space and
+	 * up to three arguments.
+	 */
+	func = (hypcall_fn_t)kern_hyp_va(host_ctxt->regs.regs[0]);
+	ret = func(host_ctxt->regs.regs[1],
+		   host_ctxt->regs.regs[2],
+		   host_ctxt->regs.regs[3]);
+	host_ctxt->regs.regs[0] = ret;
+}