[PATCH 02/15] arm64: kvm: Formalize host-hyp hypcall ABI

David Brazdil
2020-04-30T14:48:53Z

From: Quentin Perret <qperret@google.com>

In preparation for removing the hyp code from the TCB, convert the current
EL1 - EL2 KVM ABI to use hypercall numbers in lieu of direct function pointers.
While this in itself does not provide any isolation, it is a first step towards
having a properly defined EL2 ABI.

The implementation is based on a kvm_hcall_table which holds function pointers
to the hyp_text functions corresponding to each hypercall. This is highly
inspired from the arm64 sys_call_table, the main difference being the lack of
hcall wrappers at this stage.

Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: David Brazdil <dbrazdil@google.com>
---
arch/arm64/include/asm/kvm_host.h | 20 ++++++-
arch/arm64/include/asm/kvm_host_hypercalls.h | 62 ++++++++++++++++++++
arch/arm64/kvm/hyp/Makefile | 2 +-
arch/arm64/kvm/hyp/host_hypercall.c | 22 +++++++
arch/arm64/kvm/hyp/hyp-entry.S | 36 +++++++++++-
5 files changed, 137 insertions(+), 5 deletions(-)
create mode 100644 arch/arm64/include/asm/kvm_host_hypercalls.h
create mode 100644 arch/arm64/kvm/hyp/host_hypercall.c

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index e61143d6602d..5dec3b06f2b7 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -24,6 +24,7 @@
#include <asm/fpsimd.h>
#include <asm/kvm.h>
#include <asm/kvm_asm.h>
+#include <asm/kvm_host_hypercalls.h>
#include <asm/thread_info.h>
#include <asm/virt.h>

@@ -447,10 +448,25 @@ int kvm_test_age_hva(struct kvm *kvm, unsigned long hva);
void kvm_arm_halt_guest(struct kvm *kvm);
void kvm_arm_resume_guest(struct kvm *kvm);

-#define kvm_call_hyp_nvhe(hypfn, ...) \
- __kvm_call_hyp((unsigned long)kvm_ksym_ref(hypfn), ##__VA_ARGS__)
+/*
+ * Call the hypervisor via HVC. The hcall parameter must be the name of
+ * a hypercall as defined in <asm/kvm_host_hypercall.h>.
+ *
+ * Hypercalls take at most 6 parameters.
+ */
+#define kvm_call_hyp_nvhe(hcall, ...) \
+ __kvm_call_hyp(KVM_HOST_HCALL_NR(hcall), ##__VA_ARGS__)

/*
+ * u64 kvm_call_hyp(hcall, ...);
+ *
+ * Call the hypervisor. The hcall parameter must be the name of a hypercall
+ * defined in <asm/kvm_host_hypercall.h>. In the VHE case, this will be
+ * translated into a direct function call.
+ *
+ * A hcall value of less than 0xfff has a special meaning and is used to
+ * implement hyp stubs in the same way as in arch/arm64/kernel/hyp_stub.S.
+ *
* The couple of isb() below are there to guarantee the same behaviour
* on VHE as on !VHE, where the eret to EL1 acts as a context
* synchronization event.
diff --git a/arch/arm64/include/asm/kvm_host_hypercalls.h b/arch/arm64/include/asm/kvm_host_hypercalls.h
new file mode 100644
index 000000000000..af8ad505d816
--- /dev/null
+++ b/arch/arm64/include/asm/kvm_host_hypercalls.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 Google, inc
+ */
+
+#ifndef __KVM_HOST_HCALL
+#define __KVM_HOST_HCALL(x)
+#endif
+
+#define __KVM_HOST_HCALL_TABLE_IDX___kvm_enable_ssbs 0
+__KVM_HOST_HCALL(__kvm_enable_ssbs)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___kvm_get_mdcr_el2 1
+__KVM_HOST_HCALL(__kvm_get_mdcr_el2)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___kvm_timer_set_cntvoff 2
+__KVM_HOST_HCALL(__kvm_timer_set_cntvoff)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___kvm_tlb_flush_local_vmid 3
+__KVM_HOST_HCALL(__kvm_tlb_flush_local_vmid)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___kvm_flush_vm_context 4
+__KVM_HOST_HCALL(__kvm_flush_vm_context)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___kvm_vcpu_run_nvhe 5
+__KVM_HOST_HCALL(__kvm_vcpu_run_nvhe)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___kvm_tlb_flush_vmid 6
+__KVM_HOST_HCALL(__kvm_tlb_flush_vmid)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___kvm_tlb_flush_vmid_ipa 7
+__KVM_HOST_HCALL(__kvm_tlb_flush_vmid_ipa)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___vgic_v3_init_lrs 8
+__KVM_HOST_HCALL(__vgic_v3_init_lrs)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___vgic_v3_get_ich_vtr_el2 9
+__KVM_HOST_HCALL(__vgic_v3_get_ich_vtr_el2)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___vgic_v3_write_vmcr 10
+__KVM_HOST_HCALL(__vgic_v3_write_vmcr)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___vgic_v3_restore_aprs 11
+__KVM_HOST_HCALL(__vgic_v3_restore_aprs)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___vgic_v3_read_vmcr 12
+__KVM_HOST_HCALL(__vgic_v3_read_vmcr)
+
+#define __KVM_HOST_HCALL_TABLE_IDX___vgic_v3_save_aprs 13
+__KVM_HOST_HCALL(__vgic_v3_save_aprs)
+
+#define __KVM_HOST_HCALL_TABLE_IDX_SIZE 14
+
+/* XXX - Arbitrary offset for KVM-related hypercalls */
+#define __KVM_HOST_HCALL_BASE_SHIFT 8
+#define __KVM_HOST_HCALL_BASE (1ULL << __KVM_HOST_HCALL_BASE_SHIFT)
+#define __KVM_HOST_HCALL_END (__KVM_HOST_HCALL_BASE + \
+ __KVM_HOST_HCALL_TABLE_IDX_SIZE)
+
+/* Hypercall number = kvm offset + table idx */
+#define KVM_HOST_HCALL_NR(name) (__KVM_HOST_HCALL_TABLE_IDX_##name + \
+ __KVM_HOST_HCALL_BASE)
diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
index 8c9880783839..29e2b2cd2fbc 100644
--- a/arch/arm64/kvm/hyp/Makefile
+++ b/arch/arm64/kvm/hyp/Makefile
@@ -9,7 +9,7 @@ ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING \
obj-$(CONFIG_KVM) += hyp.o

hyp-y := vgic-v3-sr.o timer-sr.o aarch32.o vgic-v2-cpuif-proxy.o sysreg-sr.o \
- debug-sr.o entry.o switch.o fpsimd.o tlb.o hyp-entry.o
+ debug-sr.o entry.o switch.o fpsimd.o tlb.o host_hypercall.o hyp-entry.o

# KVM code is run at a different exception code with a different map, so
# compiler instrumentation that inserts callbacks or checks into the code may
diff --git a/arch/arm64/kvm/hyp/host_hypercall.c b/arch/arm64/kvm/hyp/host_hypercall.c
new file mode 100644
index 000000000000..6b31310f36a8
--- /dev/null
+++ b/arch/arm64/kvm/hyp/host_hypercall.c
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 Google, inc
+ */
+
+#include <asm/kvm_hyp.h>
+
+typedef long (*kvm_hcall_fn_t)(void);
+
+static long __hyp_text kvm_hc_ni(void)
+{
+ return -ENOSYS;
+}
+
+#undef __KVM_HOST_HCALL
+#define __KVM_HOST_HCALL(name) \
+ [__KVM_HOST_HCALL_TABLE_IDX_##name] = (long (*)(void))name,
+
+const kvm_hcall_fn_t kvm_hcall_table[__KVM_HOST_HCALL_TABLE_IDX_SIZE] = {
+ [0 ... __KVM_HOST_HCALL_TABLE_IDX_SIZE-1] = kvm_hc_ni,
+#include <asm/kvm_host_hypercalls.h>
+};
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index c2a13ab3c471..1a51a0958504 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -13,6 +13,7 @@
#include <asm/kvm_arm.h>
#include <asm/kvm_asm.h>
#include <asm/kvm_mmu.h>
+#include <asm/kvm_host_hypercalls.h>
#include <asm/mmu.h>

.text
@@ -21,17 +22,26 @@
.macro do_el2_call
/*
* Shuffle the parameters before calling the function
- * pointed to in x0. Assumes parameters in x[1,2,3].
+ * pointed to in x0. Assumes parameters in x[1,2,3,4,5,6].
*/
str lr, [sp, #-16]!
mov lr, x0
mov x0, x1
mov x1, x2
mov x2, x3
+ mov x3, x4
+ mov x4, x5
+ mov x5, x6
blr lr
ldr lr, [sp], #16
.endm

+/* kern_hyp_va(lm_alias(ksym)) */
+.macro ksym_hyp_va ksym, lm_offset
+ sub \ksym, \ksym, \lm_offset
+ kern_hyp_va \ksym
+.endm
+
el1_sync: // Guest trapped into EL2

mrs x0, esr_el2
@@ -66,10 +76,32 @@ el1_sync: // Guest trapped into EL2
br x5

1:
+ /* Check if the hcall number is valid */
+ cmp x0, #__KVM_HOST_HCALL_BASE
+ b.lt 2f
+ cmp x0, #__KVM_HOST_HCALL_END
+ b.lt 3f
+2:
+ mov x0, -ENOSYS
+ eret
+
+3:
+ /* Compute lm_alias() offset in x9 */
+ ldr_l x9, kimage_voffset
+ ldr_l x10, physvirt_offset
+ add x9, x9, x10
+
+ /* Find hcall function pointer in the table */
+ ldr x10, =kvm_hcall_table
+ ksym_hyp_va x10, x9
+ sub x0, x0, #__KVM_HOST_HCALL_BASE
+ add x0, x10, x0, lsl 3
+ ldr x0, [x0]
+ ksym_hyp_va x0, x9
+
/*
* Perform the EL2 call
*/
- kern_hyp_va x0
do_el2_call

eret
--
2.26.1