[PATCH 6/8] KVM: arm64: Patch kimage_voffset instead of loading the EL1 value

[Marc Zyngier]

Directly using the kimage_voffset variable is fine for now, but
will become more problematic as we start distrusting EL1.

Instead, patch the kimage_voffset into the HYP text, ensuring
we don't have to load an untrusted value later on.

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kernel/image-vars.h | 4 +---
 arch/arm64/kvm/hyp/nvhe/host.S | 7 ++++++-
 arch/arm64/kvm/va_layout.c     | 6 ++++++
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index b5b0fdd1043c..259c704a548a 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -65,13 +65,11 @@ __efistub__ctype		= _ctype;
 KVM_NVHE_ALIAS(kvm_patch_vector_branch);
 KVM_NVHE_ALIAS(kvm_update_va_mask);
 KVM_NVHE_ALIAS(kvm_update_kimg_phys_offset);
+KVM_NVHE_ALIAS(kvm_get_kimage_voffset);
 
 /* Global kernel state accessed by nVHE hyp code. */
 KVM_NVHE_ALIAS(kvm_vgic_global_state);
 
-/* Kernel constant needed to compute idmap addresses. */
-KVM_NVHE_ALIAS(kimage_voffset);
-
 /* Kernel symbols used to call panic() from nVHE hyp code (via ERET). */
 KVM_NVHE_ALIAS(__hyp_panic_string);
 KVM_NVHE_ALIAS(panic);
diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S
index ed27f06a31ba..e2d316d13180 100644
--- a/arch/arm64/kvm/hyp/nvhe/host.S
+++ b/arch/arm64/kvm/hyp/nvhe/host.S
@@ -115,7 +115,12 @@ SYM_FUNC_END(__hyp_do_panic)
 	 * Preserve x0-x4, which may contain stub parameters.
 	 */
 	ldr	x5, =__kvm_handle_stub_hvc
-	ldr_l	x6, kimage_voffset
+alternative_cb kvm_get_kimage_voffset
+	movz	x6, #0
+	movk	x6, #0, lsl #16
+	movk	x6, #0, lsl #32
+	movk	x6, #0, lsl #48
+alternative_cb_end
 
 	/* x5 = __pa(x5) */
 	sub	x5, x5, x6
diff --git a/arch/arm64/kvm/va_layout.c b/arch/arm64/kvm/va_layout.c
index 1d00d2cb93fd..d61117805de0 100644
--- a/arch/arm64/kvm/va_layout.c
+++ b/arch/arm64/kvm/va_layout.c
@@ -251,3 +251,9 @@ void kvm_update_kimg_phys_offset(struct alt_instr *alt,
 {
 	generate_mov_q(kimage_voffset + PHYS_OFFSET, origptr, updptr, nr_inst);
 }
+
+void kvm_get_kimage_voffset(struct alt_instr *alt,
+			    __le32 *origptr, __le32 *updptr, int nr_inst)
+{
+	generate_mov_q(kimage_voffset, origptr, updptr, nr_inst);
+}
-- 
2.28.0