lkml.org 
[lkml]   [2018]   [Oct]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v3 2/7] arm64/kvm: context-switch ptrauth registers
Date
From: Mark Rutland <mark.rutland@arm.com>

When pointer authentication is supported, a guest may wish to use it.
This patch adds the necessary KVM infrastructure for this to work.

When we schedule a vcpu, we enable guest usage of pointer
authentication instructions and accesses to the keys. After these are
enabled, we allow context-switching the keys.

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 attempts will result in an UNDEF
being taken by the guest.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Christoffer Dall <christoffer.dall@arm.com>
Cc: kvmarm@lists.cs.columbia.edu
---
arch/arm/include/asm/kvm_host.h | 2 +
arch/arm64/include/asm/cpufeature.h | 6 +++
arch/arm64/include/asm/kvm_host.h | 29 +++++++++++++++
arch/arm64/include/asm/kvm_hyp.h | 7 ++++
arch/arm64/kernel/traps.c | 1 +
arch/arm64/kvm/handle_exit.c | 24 +++++++-----
arch/arm64/kvm/hyp/Makefile | 1 +
arch/arm64/kvm/hyp/ptrauth-sr.c | 73 +++++++++++++++++++++++++++++++++++++
arch/arm64/kvm/hyp/switch.c | 8 ++++
arch/arm64/kvm/sys_regs.c | 40 ++++++++++++++++----
virt/kvm/arm/arm.c | 3 ++
11 files changed, 177 insertions(+), 17 deletions(-)
create mode 100644 arch/arm64/kvm/hyp/ptrauth-sr.c

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index dd32934..0ad3c3f 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -351,6 +351,8 @@ static inline int kvm_arm_have_ssbd(void)

static inline void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu) {}
static inline void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu) {}
+static inline void kvm_arm_vcpu_ptrauth_start(struct kvm_vcpu *vcpu) {}
+static inline void kvm_arm_vcpu_ptrauth_stop(struct kvm_vcpu *vcpu) {}

#define __KVM_HAVE_ARCH_VM_ALLOC
struct kvm *kvm_arch_alloc_vm(void);
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index af4ca92..967977f 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -517,6 +517,12 @@ static inline bool system_supports_sve(void)
cpus_have_const_cap(ARM64_SVE);
}

+static inline bool system_supports_ptrauth(void)
+{
+ return IS_ENABLED(CONFIG_ARM64_PTR_AUTH) &&
+ cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH);
+}
+
#define ARM64_SSBD_UNKNOWN -1
#define ARM64_SSBD_FORCE_DISABLE 0
#define ARM64_SSBD_KERNEL 1
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 0c0e243..ecba6d5 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -144,6 +144,18 @@ 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 */
@@ -426,6 +438,23 @@ static inline bool kvm_arch_check_sve_has_vhe(void)
return true;
}

+void kvm_arm_vcpu_ptrauth_enable(struct kvm_vcpu *vcpu);
+void kvm_arm_vcpu_ptrauth_disable(struct kvm_vcpu *vcpu);
+static inline void kvm_arm_vcpu_ptrauth_start(struct kvm_vcpu *vcpu)
+{
+ /* Enable ptrauth for the vcpu */
+ if (system_supports_ptrauth())
+ kvm_arm_vcpu_ptrauth_enable(vcpu);
+}
+static inline void kvm_arm_vcpu_ptrauth_stop(struct kvm_vcpu *vcpu)
+{
+ /* Disable ptrauth for the vcpu */
+ if (system_supports_ptrauth())
+ kvm_arm_vcpu_ptrauth_disable(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) {}
diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
index 384c343..3f4b844 100644
--- a/arch/arm64/include/asm/kvm_hyp.h
+++ b/arch/arm64/include/asm/kvm_hyp.h
@@ -152,6 +152,13 @@ bool __fpsimd_enabled(void);
void activate_traps_vhe_load(struct kvm_vcpu *vcpu);
void deactivate_traps_vhe_put(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/kernel/traps.c b/arch/arm64/kernel/traps.c
index 039e9ff..8c7ff96 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -557,6 +557,7 @@ static const char *esr_class_str[] = {
[ESR_ELx_EC_CP14_LS] = "CP14 LDC/STC",
[ESR_ELx_EC_FP_ASIMD] = "ASIMD",
[ESR_ELx_EC_CP10_ID] = "CP10 MRC/VMRS",
+ [ESR_ELx_EC_PAC] = "Pointer authentication trap",
[ESR_ELx_EC_CP14_64] = "CP14 MCRR/MRRC",
[ESR_ELx_EC_ILL] = "PSTATE.IL",
[ESR_ELx_EC_SVC32] = "SVC (AArch32)",
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 53759b3..798158d 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -174,19 +174,25 @@ static int handle_sve(struct kvm_vcpu *vcpu, struct kvm_run *run)
}

/*
+ * Handle the guest trying to use a ptrauth instruction, or trying to access a
+ * ptrauth register. This trap should not occur as we enable ptrauth during
+ * vcpu schedule itself but is anyway kept here for any unfortunate scenario.
+ */
+void kvm_arm_vcpu_ptrauth_trap(struct kvm_vcpu *vcpu)
+{
+ if (system_supports_ptrauth())
+ kvm_arm_vcpu_ptrauth_enable(vcpu);
+ else
+ kvm_inject_undefined(vcpu);
+}
+
+/*
* Guest usage of a ptrauth instruction (which the guest EL1 did not turn into
- * a NOP).
+ * a NOP), or guest EL1 access to a ptrauth register.
*/
static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu, struct kvm_run *run)
{
- /*
- * We don't currently support ptrauth in a guest, and we mask the ID
- * registers to prevent well-behaved guests from trying to make use of
- * it.
- *
- * Inject an UNDEF, as if the feature really isn't present.
- */
- kvm_inject_undefined(vcpu);
+ kvm_arm_vcpu_ptrauth_trap(vcpu);
return 1;
}

diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
index 2fabc2d..85ddb7f 100644
--- a/arch/arm64/kvm/hyp/Makefile
+++ b/arch/arm64/kvm/hyp/Makefile
@@ -20,6 +20,7 @@ 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 0000000..6e96908
--- /dev/null
+++ b/arch/arm64/kvm/hyp/ptrauth-sr.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * arch/arm64/kvm/hyp/ptrauth-sr.c: Guest/host ptrauth save/restore
+ *
+ * Copyright 2018 Arm Limited
+ * Author: Mark Rutland <mark.rutland@arm.com>
+ * Amit Daniel Kachhap <amit.kachhap@arm.com>
+ */
+#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>
+#include <asm/pointer_auth.h>
+
+static __always_inline 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 __always_inline void __hyp_text __ptrauth_save_state(struct kvm_cpu_context *ctxt)
+{
+ __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);
+ __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 __always_inline void __hyp_text __ptrauth_restore_state(struct kvm_cpu_context *ctxt)
+{
+ __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);
+ __ptrauth_restore_key(ctxt->sys_regs, APGA);
+}
+
+void __no_ptrauth __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 __no_ptrauth __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 fa7dab9..714ee5b 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -508,6 +508,8 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
sysreg_restore_guest_state_vhe(guest_ctxt);
__debug_switch_to_guest(vcpu);

+ __ptrauth_switch_to_guest(vcpu, host_ctxt, guest_ctxt);
+
__set_guest_arch_workaround_state(vcpu);

do {
@@ -519,6 +521,8 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)

__set_host_arch_workaround_state(vcpu);

+ __ptrauth_switch_to_host(vcpu, host_ctxt, guest_ctxt);
+
sysreg_save_guest_state_vhe(guest_ctxt);

__deactivate_traps(vcpu);
@@ -562,6 +566,8 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
__sysreg_restore_state_nvhe(guest_ctxt);
__debug_switch_to_guest(vcpu);

+ __ptrauth_switch_to_guest(vcpu, host_ctxt, guest_ctxt);
+
__set_guest_arch_workaround_state(vcpu);

do {
@@ -573,6 +579,8 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)

__set_host_arch_workaround_state(vcpu);

+ __ptrauth_switch_to_host(vcpu, host_ctxt, guest_ctxt);
+
__sysreg_save_state_nvhe(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 1ca592d..6af6c7d 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -986,6 +986,32 @@ 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)
@@ -1040,14 +1066,6 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz)
kvm_debug("SVE unsupported for guests, suppressing\n");

val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
- } else if (id == SYS_ID_AA64ISAR1_EL1) {
- const u64 ptrauth_mask = (0xfUL << ID_AA64ISAR1_APA_SHIFT) |
- (0xfUL << ID_AA64ISAR1_API_SHIFT) |
- (0xfUL << ID_AA64ISAR1_GPA_SHIFT) |
- (0xfUL << ID_AA64ISAR1_GPI_SHIFT);
- if (val & ptrauth_mask)
- kvm_debug("ptrauth unsupported for guests, suppressing\n");
- val &= ~ptrauth_mask;
} else if (id == SYS_ID_AA64MMFR1_EL1) {
if (val & (0xfUL << ID_AA64MMFR1_LOR_SHIFT))
kvm_debug("LORegions unsupported for guests, suppressing\n");
@@ -1316,6 +1334,12 @@ 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 },
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index b3d1ee4..71efc60 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -386,10 +386,13 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
vcpu_clear_wfe_traps(vcpu);
else
vcpu_set_wfe_traps(vcpu);
+
+ kvm_arm_vcpu_ptrauth_start(vcpu);
}

void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
{
+ kvm_arm_vcpu_ptrauth_stop(vcpu);
kvm_arch_vcpu_put_fp(vcpu);
kvm_vcpu_put_sysregs(vcpu);
kvm_timer_vcpu_put(vcpu);
--
2.7.4
\
 
 \ /
  Last update: 2018-10-17 12:49    [W:0.115 / U:3.372 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site