[PATCH v11 15/39] KVM: arm64: Manage GCS access and registers for guests

Mark Brown
2024-08-22T01:19:09Z

GCS introduces a number of system registers for EL1 and EL0, on systems
with GCS we need to context switch them and expose them to VMMs to allow
guests to use GCS.

In order to allow guests to use GCS we also need to configure
HCRX_EL2.GCSEn, if this is not set GCS instructions will be noops and
CHKFEAT will report GCS as disabled. Also enable fine grained traps for
access to the GCS registers by guests which do not have the feature
enabled.

In order to allow userspace to control availability of the feature to
guests we enable writability for only ID_AA64PFR1_EL1.GCS, this is a
deliberately conservative choice to avoid errors due to oversights.
Further fields should be made writable in future.

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/include/asm/kvm_host.h | 12 ++++++++
arch/arm64/include/asm/vncr_mapping.h | 2 ++
arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 49 ++++++++++++++++++++++++------
arch/arm64/kvm/sys_regs.c | 27 +++++++++++++++-
4 files changed, 79 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index a33f5996ca9f..88d6a85a2844 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -446,6 +446,10 @@ enum vcpu_sysreg {
GCR_EL1, /* Tag Control Register */
TFSRE0_EL1, /* Tag Fault Status Register (EL0) */

+ /* Guarded Control Stack registers */
+ GCSCRE0_EL1, /* Guarded Control Stack Control (EL0) */
+ GCSPR_EL0, /* Guarded Control Stack Pointer (EL0) */
+
/* 32bit specific registers. */
DACR32_EL2, /* Domain Access Control Register */
IFSR32_EL2, /* Instruction Fault Status Register */
@@ -517,6 +521,10 @@ enum vcpu_sysreg {
VNCR(PIR_EL1), /* Permission Indirection Register 1 (EL1) */
VNCR(PIRE0_EL1), /* Permission Indirection Register 0 (EL1) */

+ /* Guarded Control Stack registers */
+ VNCR(GCSPR_EL1), /* Guarded Control Stack Pointer (EL1) */
+ VNCR(GCSCR_EL1), /* Guarded Control Stack Control (EL1) */
+
VNCR(HFGRTR_EL2),
VNCR(HFGWTR_EL2),
VNCR(HFGITR_EL2),
@@ -1473,4 +1481,8 @@ void kvm_set_vm_id_reg(struct kvm *kvm, u32 reg, u64 val);
(pa + pi + pa3) == 1; \
})

+#define kvm_has_gcs(k) \
+ (system_supports_gcs() && \
+ kvm_has_feat((k), ID_AA64PFR1_EL1, GCS, IMP))
+
#endif /* __ARM64_KVM_HOST_H__ */
diff --git a/arch/arm64/include/asm/vncr_mapping.h b/arch/arm64/include/asm/vncr_mapping.h
index df2c47c55972..5e83e6f579fd 100644
--- a/arch/arm64/include/asm/vncr_mapping.h
+++ b/arch/arm64/include/asm/vncr_mapping.h
@@ -88,6 +88,8 @@
#define VNCR_PMSIRR_EL1 0x840
#define VNCR_PMSLATFR_EL1 0x848
#define VNCR_TRFCR_EL1 0x880
+#define VNCR_GCSPR_EL1 0x8C0
+#define VNCR_GCSCR_EL1 0x8D0
#define VNCR_MPAM1_EL1 0x900
#define VNCR_MPAMHCR_EL2 0x930
#define VNCR_MPAMVPMV_EL2 0x938
diff --git a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
index 4c0fdabaf8ae..ac29352e225a 100644
--- a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
+++ b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
@@ -16,6 +16,27 @@
#include <asm/kvm_hyp.h>
#include <asm/kvm_mmu.h>

+static inline struct kvm_vcpu *ctxt_to_vcpu(struct kvm_cpu_context *ctxt)
+{
+ struct kvm_vcpu *vcpu = ctxt->__hyp_running_vcpu;
+
+ if (!vcpu)
+ vcpu = container_of(ctxt, struct kvm_vcpu, arch.ctxt);
+
+ return vcpu;
+}
+
+static inline bool ctxt_has_gcs(struct kvm_cpu_context *ctxt)
+{
+ struct kvm_vcpu *vcpu;
+
+ if (!cpus_have_final_cap(ARM64_HAS_GCS))
+ return false;
+
+ vcpu = ctxt_to_vcpu(ctxt);
+ return kvm_has_feat(kern_hyp_va(vcpu->kvm), ID_AA64PFR1_EL1, GCS, IMP);
+}
+
static inline void __sysreg_save_common_state(struct kvm_cpu_context *ctxt)
{
ctxt_sys_reg(ctxt, MDSCR_EL1) = read_sysreg(mdscr_el1);
@@ -25,16 +46,10 @@ static inline void __sysreg_save_user_state(struct kvm_cpu_context *ctxt)
{
ctxt_sys_reg(ctxt, TPIDR_EL0) = read_sysreg(tpidr_el0);
ctxt_sys_reg(ctxt, TPIDRRO_EL0) = read_sysreg(tpidrro_el0);
-}
-
-static inline struct kvm_vcpu *ctxt_to_vcpu(struct kvm_cpu_context *ctxt)
-{
- struct kvm_vcpu *vcpu = ctxt->__hyp_running_vcpu;
-
- if (!vcpu)
- vcpu = container_of(ctxt, struct kvm_vcpu, arch.ctxt);
-
- return vcpu;
+ if (ctxt_has_gcs(ctxt)) {
+ ctxt_sys_reg(ctxt, GCSPR_EL0) = read_sysreg_s(SYS_GCSPR_EL0);
+ ctxt_sys_reg(ctxt, GCSCRE0_EL1) = read_sysreg_s(SYS_GCSCRE0_EL1);
+ }
}

static inline bool ctxt_has_mte(struct kvm_cpu_context *ctxt)
@@ -79,6 +94,10 @@ static inline void __sysreg_save_el1_state(struct kvm_cpu_context *ctxt)
if (ctxt_has_s1pie(ctxt)) {
ctxt_sys_reg(ctxt, PIR_EL1) = read_sysreg_el1(SYS_PIR);
ctxt_sys_reg(ctxt, PIRE0_EL1) = read_sysreg_el1(SYS_PIRE0);
+ if (ctxt_has_gcs(ctxt)) {
+ ctxt_sys_reg(ctxt, GCSPR_EL1) = read_sysreg_el1(SYS_GCSPR);
+ ctxt_sys_reg(ctxt, GCSCR_EL1) = read_sysreg_el1(SYS_GCSCR);
+ }
}
}
ctxt_sys_reg(ctxt, ESR_EL1) = read_sysreg_el1(SYS_ESR);
@@ -126,6 +145,11 @@ static inline void __sysreg_restore_user_state(struct kvm_cpu_context *ctxt)
{
write_sysreg(ctxt_sys_reg(ctxt, TPIDR_EL0), tpidr_el0);
write_sysreg(ctxt_sys_reg(ctxt, TPIDRRO_EL0), tpidrro_el0);
+ if (ctxt_has_gcs(ctxt)) {
+ write_sysreg_s(ctxt_sys_reg(ctxt, GCSPR_EL0), SYS_GCSPR_EL0);
+ write_sysreg_s(ctxt_sys_reg(ctxt, GCSCRE0_EL1),
+ SYS_GCSCRE0_EL1);
+ }
}

static inline void __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt)
@@ -157,6 +181,11 @@ static inline void __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt)
if (ctxt_has_s1pie(ctxt)) {
write_sysreg_el1(ctxt_sys_reg(ctxt, PIR_EL1), SYS_PIR);
write_sysreg_el1(ctxt_sys_reg(ctxt, PIRE0_EL1), SYS_PIRE0);
+
+ if (ctxt_has_gcs(ctxt)) {
+ write_sysreg_el1(ctxt_sys_reg(ctxt, GCSPR_EL1), SYS_GCSPR);
+ write_sysreg_el1(ctxt_sys_reg(ctxt, GCSCR_EL1), SYS_GCSCR);
+ }
}
}
write_sysreg_el1(ctxt_sys_reg(ctxt, ESR_EL1), SYS_ESR);
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index c90324060436..4e820dd50414 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1645,6 +1645,15 @@ static unsigned int raz_visibility(const struct kvm_vcpu *vcpu,
return REG_RAZ;
}

+static unsigned int gcs_visibility(const struct kvm_vcpu *vcpu,
+ const struct sys_reg_desc *r)
+{
+ if (kvm_has_gcs(vcpu->kvm))
+ return 0;
+
+ return REG_HIDDEN;
+}
+
/* cpufeature ID register access trap handlers */

static bool access_id_reg(struct kvm_vcpu *vcpu,
@@ -2362,7 +2371,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
ID_AA64PFR0_EL1_GIC |
ID_AA64PFR0_EL1_AdvSIMD |
ID_AA64PFR0_EL1_FP), },
- ID_SANITISED(ID_AA64PFR1_EL1),
+ ID_WRITABLE(ID_AA64PFR1_EL1, ID_AA64PFR1_EL1_GCS),
ID_UNALLOCATED(4,2),
ID_UNALLOCATED(4,3),
ID_WRITABLE(ID_AA64ZFR0_EL1, ~ID_AA64ZFR0_EL1_RES0),
@@ -2446,6 +2455,13 @@ static const struct sys_reg_desc sys_reg_descs[] = {
PTRAUTH_KEY(APDB),
PTRAUTH_KEY(APGA),

+ { SYS_DESC(SYS_GCSCR_EL1), NULL, reset_val, GCSCR_EL1, 0,
+ .visibility = gcs_visibility },
+ { SYS_DESC(SYS_GCSPR_EL1), NULL, reset_unknown, GCSPR_EL1,
+ .visibility = gcs_visibility },
+ { SYS_DESC(SYS_GCSCRE0_EL1), NULL, reset_val, GCSCRE0_EL1, 0,
+ .visibility = gcs_visibility },
+
{ SYS_DESC(SYS_SPSR_EL1), access_spsr},
{ SYS_DESC(SYS_ELR_EL1), access_elr},

@@ -2535,6 +2551,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
CTR_EL0_IDC_MASK |
CTR_EL0_DminLine_MASK |
CTR_EL0_IminLine_MASK),
+ { SYS_DESC(SYS_GCSPR_EL0), NULL, reset_unknown, GCSPR_EL0,
+ .visibility = gcs_visibility },
{ SYS_DESC(SYS_SVCR), undef_access },

{ PMU_SYS_REG(PMCR_EL0), .access = access_pmcr, .reset = reset_pmcr,
@@ -4560,6 +4578,9 @@ void kvm_calculate_traps(struct kvm_vcpu *vcpu)

if (kvm_has_feat(kvm, ID_AA64MMFR3_EL1, TCRX, IMP))
vcpu->arch.hcrx_el2 |= HCRX_EL2_TCR2En;
+
+ if (kvm_has_gcs(kvm))
+ vcpu->arch.hcrx_el2 |= HCRX_EL2_GCSEn;
}

if (test_bit(KVM_ARCH_FLAG_FGU_INITIALIZED, &kvm->arch.flags))
@@ -4604,6 +4625,10 @@ void kvm_calculate_traps(struct kvm_vcpu *vcpu)
kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nPIRE0_EL1 |
HFGxTR_EL2_nPIR_EL1);

+ if (!kvm_has_gcs(kvm))
+ kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nGCS_EL0 |
+ HFGxTR_EL2_nGCS_EL1);
+
if (!kvm_has_feat(kvm, ID_AA64PFR0_EL1, AMU, IMP))
kvm->arch.fgu[HAFGRTR_GROUP] |= ~(HAFGRTR_EL2_RES0 |
HAFGRTR_EL2_RES1);

--
2.39.2