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Subject[PATCHv2 10/12] arm64/kvm: context-switch ptrauth registers
Date
When pointer authentication is supported, a guest may wish to use it.
This patch adds the necessary KVM infrastructure for this to work, with
a semi-lazy context switch of the pointer auth state.

When we schedule a vcpu, we disable guest usage of pointer
authentication instructions and accesses to the keys. While these are
disabled, we avoid context-switching the keys. When we trap the guest
trying to use pointer authentication functionality, we change to eagerly
context-switching the keys, and enable the feature. The next time the
vcpu is scheduled out/in, we start again.

Pointer authentication consists of address authentication and generic
authentication, and CPUs in a system might have varied support for
either. Where support for either feature is not uniform, it is hidden
from guests via ID register emulation, as a result of the cpufeature
framework in the host.

Unfortunately, address authentication and generic authentication cannot
be trapped separately, as the architecture provides a single EL2 trap
covering both. If we wish to expose one without the other, we cannot
prevent a (badly-written) guest from intermittently using a feature
which is not uniformly supported (when scheduled on a physical CPU which
supports the relevant feature). When the guest is scheduled on a
physical CPU lacking the feature, these atetmps will result in an UNDEF
being taken by the guest.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Christoffer Dall <cdall@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: kvmarm@lists.cs.columbia.edu
---
arch/arm64/include/asm/kvm_host.h | 23 +++++++++-
arch/arm64/include/asm/kvm_hyp.h | 7 +++
arch/arm64/kvm/handle_exit.c | 21 +++++++++
arch/arm64/kvm/hyp/Makefile | 1 +
arch/arm64/kvm/hyp/ptrauth-sr.c | 91 +++++++++++++++++++++++++++++++++++++++
arch/arm64/kvm/hyp/switch.c | 4 ++
arch/arm64/kvm/sys_regs.c | 32 ++++++++++++++
7 files changed, 178 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/kvm/hyp/ptrauth-sr.c

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 39184aa3e2f2..2fc21a2a75a7 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -136,6 +136,18 @@ enum vcpu_sysreg {
PMSWINC_EL0, /* Software Increment Register */
PMUSERENR_EL0, /* User Enable Register */

+ /* Pointer Authentication Registers */
+ APIAKEYLO_EL1,
+ APIAKEYHI_EL1,
+ APIBKEYLO_EL1,
+ APIBKEYHI_EL1,
+ APDAKEYLO_EL1,
+ APDAKEYHI_EL1,
+ APDBKEYLO_EL1,
+ APDBKEYHI_EL1,
+ APGAKEYLO_EL1,
+ APGAKEYHI_EL1,
+
/* 32bit specific registers. Keep them at the end of the range */
DACR32_EL2, /* Domain Access Control Register */
IFSR32_EL2, /* Instruction Fault Status Register */
@@ -363,10 +375,19 @@ static inline void __cpu_init_hyp_mode(phys_addr_t pgd_ptr,
__kvm_call_hyp((void *)pgd_ptr, hyp_stack_ptr, vector_ptr);
}

+void kvm_arm_vcpu_ptrauth_enable(struct kvm_vcpu *vcpu);
+void kvm_arm_vcpu_ptrauth_disable(struct kvm_vcpu *vcpu);
+void kvm_arm_vcpu_ptrauth_trap(struct kvm_vcpu *vcpu);
+
static inline void kvm_arch_hardware_unsetup(void) {}
static inline void kvm_arch_sync_events(struct kvm *kvm) {}
static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
-static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
+
+static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu)
+{
+ kvm_arm_vcpu_ptrauth_disable(vcpu);
+}
+
static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}

void kvm_arm_init_debug(void);
diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
index 08d3bb66c8b7..d0dd924cb175 100644
--- a/arch/arm64/include/asm/kvm_hyp.h
+++ b/arch/arm64/include/asm/kvm_hyp.h
@@ -152,6 +152,13 @@ void __fpsimd_save_state(struct user_fpsimd_state *fp_regs);
void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs);
bool __fpsimd_enabled(void);

+void __ptrauth_switch_to_guest(struct kvm_vcpu *vcpu,
+ struct kvm_cpu_context *host_ctxt,
+ struct kvm_cpu_context *guest_ctxt);
+void __ptrauth_switch_to_host(struct kvm_vcpu *vcpu,
+ struct kvm_cpu_context *host_ctxt,
+ struct kvm_cpu_context *guest_ctxt);
+
u64 __guest_enter(struct kvm_vcpu *vcpu, struct kvm_cpu_context *host_ctxt);
void __noreturn __hyp_do_panic(unsigned long, ...);

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index b71247995469..d9aff3c86551 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -136,6 +136,26 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu, struct kvm_run *run)
return ret;
}

+/*
+ * Handle the guest trying to use a ptrauth instruction, or trying to access a
+ * ptrauth register.
+ */
+void kvm_arm_vcpu_ptrauth_trap(struct kvm_vcpu *vcpu)
+{
+ if (cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH) ||
+ cpus_have_const_cap(ARM64_HAS_GENERIC_AUTH)) {
+ kvm_arm_vcpu_ptrauth_enable(vcpu);
+ } else {
+ kvm_inject_undefined(vcpu);
+ }
+}
+
+static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu, struct kvm_run *run)
+{
+ kvm_arm_vcpu_ptrauth_trap(vcpu);
+ return 1;
+}
+
static int kvm_handle_unknown_ec(struct kvm_vcpu *vcpu, struct kvm_run *run)
{
u32 hsr = kvm_vcpu_get_hsr(vcpu);
@@ -176,6 +196,7 @@ static exit_handle_fn arm_exit_handlers[] = {
[ESR_ELx_EC_BKPT32] = kvm_handle_guest_debug,
[ESR_ELx_EC_BRK64] = kvm_handle_guest_debug,
[ESR_ELx_EC_FP_ASIMD] = handle_no_fpsimd,
+ [ESR_ELx_EC_PAC] = kvm_handle_ptrauth,
};

static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
index f04400d494b7..2c2c3bd90cc0 100644
--- a/arch/arm64/kvm/hyp/Makefile
+++ b/arch/arm64/kvm/hyp/Makefile
@@ -19,6 +19,7 @@ obj-$(CONFIG_KVM_ARM_HOST) += fpsimd.o
obj-$(CONFIG_KVM_ARM_HOST) += tlb.o
obj-$(CONFIG_KVM_ARM_HOST) += hyp-entry.o
obj-$(CONFIG_KVM_ARM_HOST) += s2-setup.o
+obj-$(CONFIG_KVM_ARM_HOST) += ptrauth-sr.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/ptrauth-sr.c b/arch/arm64/kvm/hyp/ptrauth-sr.c
new file mode 100644
index 000000000000..2784fb373296
--- /dev/null
+++ b/arch/arm64/kvm/hyp/ptrauth-sr.c
@@ -0,0 +1,91 @@
+/*
+ * Copyright (C) 2017 ARM Ltd
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/compiler.h>
+#include <linux/kvm_host.h>
+
+#include <asm/cpucaps.h>
+#include <asm/cpufeature.h>
+#include <asm/kvm_asm.h>
+#include <asm/kvm_hyp.h>
+
+static bool __hyp_text __ptrauth_is_enabled(struct kvm_vcpu *vcpu)
+{
+ return vcpu->arch.hcr_el2 & (HCR_API | HCR_APK);
+}
+
+#define __ptrauth_save_key(regs, key) \
+({ \
+ regs[key ## KEYLO_EL1] = read_sysreg_s(SYS_ ## key ## KEYLO_EL1); \
+ regs[key ## KEYHI_EL1] = read_sysreg_s(SYS_ ## key ## KEYHI_EL1); \
+})
+
+static void __hyp_text __ptrauth_save_state(struct kvm_cpu_context *ctxt)
+{
+ if (cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH)) {
+ __ptrauth_save_key(ctxt->sys_regs, APIA);
+ __ptrauth_save_key(ctxt->sys_regs, APIB);
+ __ptrauth_save_key(ctxt->sys_regs, APDA);
+ __ptrauth_save_key(ctxt->sys_regs, APDB);
+ }
+
+ if (cpus_have_const_cap(ARM64_HAS_GENERIC_AUTH)) {
+ __ptrauth_save_key(ctxt->sys_regs, APGA);
+ }
+}
+
+#define __ptrauth_restore_key(regs, key) \
+({ \
+ write_sysreg_s(regs[key ## KEYLO_EL1], SYS_ ## key ## KEYLO_EL1); \
+ write_sysreg_s(regs[key ## KEYHI_EL1], SYS_ ## key ## KEYHI_EL1); \
+})
+
+static void __hyp_text __ptrauth_restore_state(struct kvm_cpu_context *ctxt)
+{
+
+ if (cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH)) {
+ __ptrauth_restore_key(ctxt->sys_regs, APIA);
+ __ptrauth_restore_key(ctxt->sys_regs, APIB);
+ __ptrauth_restore_key(ctxt->sys_regs, APDA);
+ __ptrauth_restore_key(ctxt->sys_regs, APDB);
+ }
+
+ if (cpus_have_const_cap(ARM64_HAS_GENERIC_AUTH)) {
+ __ptrauth_restore_key(ctxt->sys_regs, APGA);
+ }
+}
+
+void __hyp_text __ptrauth_switch_to_guest(struct kvm_vcpu *vcpu,
+ struct kvm_cpu_context *host_ctxt,
+ struct kvm_cpu_context *guest_ctxt)
+{
+ if (!__ptrauth_is_enabled(vcpu))
+ return;
+
+ __ptrauth_save_state(host_ctxt);
+ __ptrauth_restore_state(guest_ctxt);
+}
+
+void __hyp_text __ptrauth_switch_to_host(struct kvm_vcpu *vcpu,
+ struct kvm_cpu_context *host_ctxt,
+ struct kvm_cpu_context *guest_ctxt)
+{
+ if (!__ptrauth_is_enabled(vcpu))
+ return;
+
+ __ptrauth_save_state(guest_ctxt);
+ __ptrauth_restore_state(host_ctxt);
+}
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index 2205f0be3ced..d9be2762ac1a 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -315,6 +315,8 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
__sysreg_restore_guest_state(guest_ctxt);
__debug_restore_state(vcpu, kern_hyp_va(vcpu->arch.debug_ptr), guest_ctxt);

+ __ptrauth_switch_to_guest(vcpu, host_ctxt, guest_ctxt);
+
/* Jump in the fire! */
again:
exit_code = __guest_enter(vcpu, host_ctxt);
@@ -373,6 +375,8 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)

fp_enabled = __fpsimd_enabled();

+ __ptrauth_switch_to_host(vcpu, host_ctxt, guest_ctxt);
+
__sysreg_save_guest_state(guest_ctxt);
__sysreg32_save_state(vcpu);
__timer_disable_traps(vcpu);
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 1830ebc227d1..5fe3b2588bec 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -838,6 +838,32 @@ static bool access_pmuserenr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
{ SYS_DESC(SYS_PMEVTYPERn_EL0(n)), \
access_pmu_evtyper, reset_unknown, (PMEVTYPER0_EL0 + n), }

+
+void kvm_arm_vcpu_ptrauth_enable(struct kvm_vcpu *vcpu)
+{
+ vcpu->arch.hcr_el2 |= (HCR_API | HCR_APK);
+}
+
+void kvm_arm_vcpu_ptrauth_disable(struct kvm_vcpu *vcpu)
+{
+ vcpu->arch.hcr_el2 &= ~(HCR_API | HCR_APK);
+}
+
+static bool trap_ptrauth(struct kvm_vcpu *vcpu,
+ struct sys_reg_params *p,
+ const struct sys_reg_desc *rd)
+{
+ kvm_arm_vcpu_ptrauth_trap(vcpu);
+ return false;
+}
+
+#define __PTRAUTH_KEY(k) \
+ { SYS_DESC(SYS_## k), trap_ptrauth, reset_unknown, k }
+
+#define PTRAUTH_KEY(k) \
+ __PTRAUTH_KEY(k ## KEYLO_EL1), \
+ __PTRAUTH_KEY(k ## KEYHI_EL1)
+
static bool access_cntp_tval(struct kvm_vcpu *vcpu,
struct sys_reg_params *p,
const struct sys_reg_desc *r)
@@ -1156,6 +1182,12 @@ static const struct sys_reg_desc sys_reg_descs[] = {
{ SYS_DESC(SYS_TTBR1_EL1), access_vm_reg, reset_unknown, TTBR1_EL1 },
{ SYS_DESC(SYS_TCR_EL1), access_vm_reg, reset_val, TCR_EL1, 0 },

+ PTRAUTH_KEY(APIA),
+ PTRAUTH_KEY(APIB),
+ PTRAUTH_KEY(APDA),
+ PTRAUTH_KEY(APDB),
+ PTRAUTH_KEY(APGA),
+
{ SYS_DESC(SYS_AFSR0_EL1), access_vm_reg, reset_unknown, AFSR0_EL1 },
{ SYS_DESC(SYS_AFSR1_EL1), access_vm_reg, reset_unknown, AFSR1_EL1 },
{ SYS_DESC(SYS_ESR_EL1), access_vm_reg, reset_unknown, ESR_EL1 },
--
2.11.0
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