[PATCH v5 3/7] arm64/kvm: disable access to AMU registers from kvm guests

Ionela Voinescu
2020-02-26T13:30:46Z

Access to the AMU counters should be disabled by default in kvm guests,
as information from the counters might reveal activity in other guests
or activity on the host.

Therefore, disable access to AMU registers from EL0 and EL1 in kvm
guests by:
- Hiding the presence of the extension in the feature register
(SYS_ID_AA64PFR0_EL1) on the VCPU.
- Disabling access to the AMU registers before switching to the guest.
- Trapping accesses and injecting an undefined instruction into the
guest.

Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/kvm_arm.h | 1 +
arch/arm64/kvm/hyp/switch.c | 14 ++++-
arch/arm64/kvm/sys_regs.c | 93 +++++++++++++++++++++++++++++++-
3 files changed, 105 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
index 6e5d839f42b5..51c1d9918999 100644
--- a/arch/arm64/include/asm/kvm_arm.h
+++ b/arch/arm64/include/asm/kvm_arm.h
@@ -267,6 +267,7 @@

/* Hyp Coprocessor Trap Register */
#define CPTR_EL2_TCPAC (1 << 31)
+#define CPTR_EL2_TAM (1 << 30)
#define CPTR_EL2_TTA (1 << 20)
#define CPTR_EL2_TFP (1 << CPTR_EL2_TFP_SHIFT)
#define CPTR_EL2_TZ (1 << 8)
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index dfe8dd172512..46292a370781 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -98,6 +98,18 @@ static void activate_traps_vhe(struct kvm_vcpu *vcpu)
val = read_sysreg(cpacr_el1);
val |= CPACR_EL1_TTA;
val &= ~CPACR_EL1_ZEN;
+
+ /*
+ * With VHE (HCR.E2H == 1), accesses to CPACR_EL1 are routed to
+ * CPTR_EL2. In general, CPACR_EL1 has the same layout as CPTR_EL2,
+ * except for some missing controls, such as TAM.
+ * In this case, CPTR_EL2.TAM has the same position with or without
+ * VHE (HCR.E2H == 1) which allows us to use here the CPTR_EL2.TAM
+ * shift value for trapping the AMU accesses.
+ */
+
+ val |= CPTR_EL2_TAM;
+
if (update_fp_enabled(vcpu)) {
if (vcpu_has_sve(vcpu))
val |= CPACR_EL1_ZEN;
@@ -119,7 +131,7 @@ static void __hyp_text __activate_traps_nvhe(struct kvm_vcpu *vcpu)
__activate_traps_common(vcpu);

val = CPTR_EL2_DEFAULT;
- val |= CPTR_EL2_TTA | CPTR_EL2_TZ;
+ val |= CPTR_EL2_TTA | CPTR_EL2_TZ | CPTR_EL2_TAM;
if (!update_fp_enabled(vcpu)) {
val |= CPTR_EL2_TFP;
__activate_traps_fpsimd32(vcpu);
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 3e909b117f0c..44354c812783 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1003,6 +1003,20 @@ 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), }

+static bool access_amu(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
+ const struct sys_reg_desc *r)
+{
+ kvm_inject_undefined(vcpu);
+
+ return false;
+}
+
+/* Macro to expand the AMU counter and type registers*/
+#define AMU_AMEVCNTR0_EL0(n) { SYS_DESC(SYS_AMEVCNTR0_EL0(n)), access_amu }
+#define AMU_AMEVTYPE0_EL0(n) { SYS_DESC(SYS_AMEVTYPE0_EL0(n)), access_amu }
+#define AMU_AMEVCNTR1_EL0(n) { SYS_DESC(SYS_AMEVCNTR1_EL0(n)), access_amu }
+#define AMU_AMEVTYPE1_EL0(n) { SYS_DESC(SYS_AMEVTYPE1_EL0(n)), access_amu }
+
static bool trap_ptrauth(struct kvm_vcpu *vcpu,
struct sys_reg_params *p,
const struct sys_reg_desc *rd)
@@ -1078,8 +1092,10 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
(u32)r->CRn, (u32)r->CRm, (u32)r->Op2);
u64 val = raz ? 0 : read_sanitised_ftr_reg(id);

- if (id == SYS_ID_AA64PFR0_EL1 && !vcpu_has_sve(vcpu)) {
- val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
+ if (id == SYS_ID_AA64PFR0_EL1) {
+ if (!vcpu_has_sve(vcpu))
+ val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
+ val &= ~(0xfUL << ID_AA64PFR0_AMU_SHIFT);
} else if (id == SYS_ID_AA64ISAR1_EL1 && !vcpu_has_ptrauth(vcpu)) {
val &= ~((0xfUL << ID_AA64ISAR1_APA_SHIFT) |
(0xfUL << ID_AA64ISAR1_API_SHIFT) |
@@ -1565,6 +1581,79 @@ static const struct sys_reg_desc sys_reg_descs[] = {
{ SYS_DESC(SYS_TPIDR_EL0), NULL, reset_unknown, TPIDR_EL0 },
{ SYS_DESC(SYS_TPIDRRO_EL0), NULL, reset_unknown, TPIDRRO_EL0 },

+ { SYS_DESC(SYS_AMCR_EL0), access_amu },
+ { SYS_DESC(SYS_AMCFGR_EL0), access_amu },
+ { SYS_DESC(SYS_AMCGCR_EL0), access_amu },
+ { SYS_DESC(SYS_AMUSERENR_EL0), access_amu },
+ { SYS_DESC(SYS_AMCNTENCLR0_EL0), access_amu },
+ { SYS_DESC(SYS_AMCNTENSET0_EL0), access_amu },
+ { SYS_DESC(SYS_AMCNTENCLR1_EL0), access_amu },
+ { SYS_DESC(SYS_AMCNTENSET1_EL0), access_amu },
+ AMU_AMEVCNTR0_EL0(0),
+ AMU_AMEVCNTR0_EL0(1),
+ AMU_AMEVCNTR0_EL0(2),
+ AMU_AMEVCNTR0_EL0(3),
+ AMU_AMEVCNTR0_EL0(4),
+ AMU_AMEVCNTR0_EL0(5),
+ AMU_AMEVCNTR0_EL0(6),
+ AMU_AMEVCNTR0_EL0(7),
+ AMU_AMEVCNTR0_EL0(8),
+ AMU_AMEVCNTR0_EL0(9),
+ AMU_AMEVCNTR0_EL0(10),
+ AMU_AMEVCNTR0_EL0(11),
+ AMU_AMEVCNTR0_EL0(12),
+ AMU_AMEVCNTR0_EL0(13),
+ AMU_AMEVCNTR0_EL0(14),
+ AMU_AMEVCNTR0_EL0(15),
+ AMU_AMEVTYPE0_EL0(0),
+ AMU_AMEVTYPE0_EL0(1),
+ AMU_AMEVTYPE0_EL0(2),
+ AMU_AMEVTYPE0_EL0(3),
+ AMU_AMEVTYPE0_EL0(4),
+ AMU_AMEVTYPE0_EL0(5),
+ AMU_AMEVTYPE0_EL0(6),
+ AMU_AMEVTYPE0_EL0(7),
+ AMU_AMEVTYPE0_EL0(8),
+ AMU_AMEVTYPE0_EL0(9),
+ AMU_AMEVTYPE0_EL0(10),
+ AMU_AMEVTYPE0_EL0(11),
+ AMU_AMEVTYPE0_EL0(12),
+ AMU_AMEVTYPE0_EL0(13),
+ AMU_AMEVTYPE0_EL0(14),
+ AMU_AMEVTYPE0_EL0(15),
+ AMU_AMEVCNTR1_EL0(0),
+ AMU_AMEVCNTR1_EL0(1),
+ AMU_AMEVCNTR1_EL0(2),
+ AMU_AMEVCNTR1_EL0(3),
+ AMU_AMEVCNTR1_EL0(4),
+ AMU_AMEVCNTR1_EL0(5),
+ AMU_AMEVCNTR1_EL0(6),
+ AMU_AMEVCNTR1_EL0(7),
+ AMU_AMEVCNTR1_EL0(8),
+ AMU_AMEVCNTR1_EL0(9),
+ AMU_AMEVCNTR1_EL0(10),
+ AMU_AMEVCNTR1_EL0(11),
+ AMU_AMEVCNTR1_EL0(12),
+ AMU_AMEVCNTR1_EL0(13),
+ AMU_AMEVCNTR1_EL0(14),
+ AMU_AMEVCNTR1_EL0(15),
+ AMU_AMEVTYPE1_EL0(0),
+ AMU_AMEVTYPE1_EL0(1),
+ AMU_AMEVTYPE1_EL0(2),
+ AMU_AMEVTYPE1_EL0(3),
+ AMU_AMEVTYPE1_EL0(4),
+ AMU_AMEVTYPE1_EL0(5),
+ AMU_AMEVTYPE1_EL0(6),
+ AMU_AMEVTYPE1_EL0(7),
+ AMU_AMEVTYPE1_EL0(8),
+ AMU_AMEVTYPE1_EL0(9),
+ AMU_AMEVTYPE1_EL0(10),
+ AMU_AMEVTYPE1_EL0(11),
+ AMU_AMEVTYPE1_EL0(12),
+ AMU_AMEVTYPE1_EL0(13),
+ AMU_AMEVTYPE1_EL0(14),
+ AMU_AMEVTYPE1_EL0(15),
+
{ SYS_DESC(SYS_CNTP_TVAL_EL0), access_arch_timer },
{ SYS_DESC(SYS_CNTP_CTL_EL0), access_arch_timer },
{ SYS_DESC(SYS_CNTP_CVAL_EL0), access_arch_timer },
--
2.17.1