diff options
| author | Oliver Upton | 2022-02-03 17:41:57 +0000 |
|---|---|---|
| committer | Marc Zyngier | 2022-02-08 14:23:41 +0000 |
| commit | 7dabf02f43a1670d13282463fc0106f01dfd6f9c (patch) | |
| tree | 1051af3f34505cffca6918de7024352ca7d7c9b4 /arch/arm64/kvm | |
| parent | f24adc65c5568a8d94e2693f5441de80f1ffe0d3 (diff) | |
KVM: arm64: Emulate the OS Lock
The OS lock blocks all debug exceptions at every EL. To date, KVM has
not implemented the OS lock for its guests, despite the fact that it is
mandatory per the architecture. Simple context switching between the
guest and host is not appropriate, as its effects are not constrained to
the guest context.
Emulate the OS Lock by clearing MDE and SS in MDSCR_EL1, thereby
blocking all but software breakpoint instructions.
Signed-off-by: Oliver Upton <oupton@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220203174159.2887882-5-oupton@google.com
Diffstat (limited to 'arch/arm64/kvm')
| -rw-r--r-- | arch/arm64/kvm/debug.c | 26 | ||||
| -rw-r--r-- | arch/arm64/kvm/sys_regs.c | 6 |
2 files changed, 25 insertions, 7 deletions
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c index db9361338b2a..4fd5c216c4bb 100644 --- a/arch/arm64/kvm/debug.c +++ b/arch/arm64/kvm/debug.c @@ -105,9 +105,11 @@ static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu) * - Userspace is using the hardware to debug the guest * (KVM_GUESTDBG_USE_HW is set). * - The guest is not using debug (KVM_ARM64_DEBUG_DIRTY is clear). + * - The guest has enabled the OS Lock (debug exceptions are blocked). */ if ((vcpu->guest_debug & KVM_GUESTDBG_USE_HW) || - !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY)) + !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY) || + kvm_vcpu_os_lock_enabled(vcpu)) vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA; trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2); @@ -160,8 +162,8 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) kvm_arm_setup_mdcr_el2(vcpu); - /* Is Guest debugging in effect? */ - if (vcpu->guest_debug) { + /* Check if we need to use the debug registers. */ + if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) { /* Save guest debug state */ save_guest_debug_regs(vcpu); @@ -223,6 +225,19 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) trace_kvm_arm_set_regset("WAPTS", get_num_wrps(), &vcpu->arch.debug_ptr->dbg_wcr[0], &vcpu->arch.debug_ptr->dbg_wvr[0]); + + /* + * The OS Lock blocks debug exceptions in all ELs when it is + * enabled. If the guest has enabled the OS Lock, constrain its + * effects to the guest. Emulate the behavior by clearing + * MDSCR_EL1.MDE. In so doing, we ensure that host debug + * exceptions are unaffected by guest configuration of the OS + * Lock. + */ + } else if (kvm_vcpu_os_lock_enabled(vcpu)) { + mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1); + mdscr &= ~DBG_MDSCR_MDE; + vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1); } } @@ -244,7 +259,10 @@ void kvm_arm_clear_debug(struct kvm_vcpu *vcpu) { trace_kvm_arm_clear_debug(vcpu->guest_debug); - if (vcpu->guest_debug) { + /* + * Restore the guest's debug registers if we were using them. + */ + if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) { restore_guest_debug_regs(vcpu); /* diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index b0d7240ef49f..dd34b5ab51d4 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -1457,9 +1457,9 @@ static unsigned int mte_visibility(const struct kvm_vcpu *vcpu, * Debug handling: We do trap most, if not all debug related system * registers. The implementation is good enough to ensure that a guest * can use these with minimal performance degradation. The drawback is - * that we don't implement any of the external debug, none of the - * OSlock protocol. This should be revisited if we ever encounter a - * more demanding guest... + * that we don't implement any of the external debug architecture. + * This should be revisited if we ever encounter a more demanding + * guest... */ static const struct sys_reg_desc sys_reg_descs[] = { { SYS_DESC(SYS_DC_ISW), access_dcsw }, |