[PATCH 11/17] KVM: arm64: Prevent host PC adjustments for protected vCPUs
From: Fuad Tabba <fuad.tabba@linux.dev>
Date: 2026-08-31 16:35:00
Also in:
kvmarm, lkml
Subsystem:
arm64 port (aarch64 architecture), kernel virtual machine for arm64 (kvm/arm64), the rest · Maintainers:
Catalin Marinas, Will Deacon, Marc Zyngier, Oliver Upton, Linus Torvalds
__kvm_adjust_pc() lets the host advance a vCPU's PC or inject an exception, which for a protected vCPU would let the host redirect guest execution. Drop the request there: the entry handlers apply the host's PC_UPDATE_REQ on re-entry, where EL2 allows it. For a non-protected vCPU, adjusting the hyp vCPU while PKVM_HOST_STATE_DIRTY is set loses the update at the next flush and the guest re-executes an emulated MMIO access, so the flag selects which copy to adjust. Adjusting the hyp vCPU copies PC_UPDATE_REQ in and back out again. Without the copy back, INCREMENT_PC outlives the adjustment and the next KVM_SET_VCPU_EVENTS trips WARN_ON(INCREMENT_PC) in kvm_pend_exception(). Unloaded, the host copy is host-writable, so pin it and its VM before adjusting. Only commit_pending_events(), under KVM_SET_VCPU_EVENTS, reaches EL2 with no hyp vCPU loaded. KVM_RUN's call always has one. enter_exception64() reads the VM's MTE flag and a host copy's vcpu->kvm is host-written, so __kvm_adjust_pc_vm() takes the VM as a parameter: the pinned host struct kvm when unloaded, the hyp VM otherwise. Suggested-by: Marc Zyngier <maz@kernel.org> Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev> --- arch/arm64/include/asm/kvm_asm.h | 1 + arch/arm64/kvm/hyp/exception.c | 27 ++++++++++------- arch/arm64/kvm/hyp/nvhe/hyp-main.c | 47 +++++++++++++++++++++++++++++- 3 files changed, 63 insertions(+), 12 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index e5b92ac09e69e..d149afee7b4bd 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h@@ -280,6 +280,7 @@ extern int __kvm_at_s12(struct kvm_vcpu *vcpu, u32 op, u64 vaddr); extern int __kvm_vcpu_run(struct kvm_vcpu *vcpu); extern void __kvm_adjust_pc(struct kvm_vcpu *vcpu); +extern void __kvm_adjust_pc_vm(struct kvm_vcpu *vcpu, struct kvm *kvm); extern bool __vgic_v3_get_gic_config(void); extern void __vgic_v3_init_lrs(void);
diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c
index 754e2dc1df54a..bf9d8efce9984 100644
--- a/arch/arm64/kvm/hyp/exception.c
+++ b/arch/arm64/kvm/hyp/exception.c@@ -66,8 +66,8 @@ static void __vcpu_write_spsr_und(struct kvm_vcpu *vcpu, u64 val) * Here we manipulate the fields in order of the AArch64 SPSR_ELx layout, from * MSB to LSB. */ -static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode, - enum exception_type type) +static void enter_exception64(struct kvm_vcpu *vcpu, struct kvm *kvm, + unsigned long target_mode, enum exception_type type) { unsigned long sctlr, vbar, old, new, mode; u64 exc_offset;
@@ -109,7 +109,7 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode, new |= (old & PSR_C_BIT); new |= (old & PSR_V_BIT); - if (kvm_has_mte(kern_hyp_va(vcpu->kvm))) + if (kvm_has_mte(kvm)) new |= PSR_TCO_BIT; new |= (old & PSR_DIT_BIT);
@@ -294,7 +294,7 @@ static void enter_exception32(struct kvm_vcpu *vcpu, u32 mode, u32 vect_offset) *vcpu_pc(vcpu) = vect_offset; } -static void kvm_inject_exception(struct kvm_vcpu *vcpu) +static void kvm_inject_exception(struct kvm_vcpu *vcpu, struct kvm *kvm) { if (vcpu_el1_is_32bit(vcpu)) { switch (vcpu_get_flag(vcpu, EXCEPT_MASK)) {
@@ -314,23 +314,23 @@ static void kvm_inject_exception(struct kvm_vcpu *vcpu) } else { switch (vcpu_get_flag(vcpu, EXCEPT_MASK)) { case unpack_vcpu_flag(EXCEPT_AA64_EL1_SYNC): - enter_exception64(vcpu, PSR_MODE_EL1h, except_type_sync); + enter_exception64(vcpu, kvm, PSR_MODE_EL1h, except_type_sync); break; case unpack_vcpu_flag(EXCEPT_AA64_EL1_SERR): - enter_exception64(vcpu, PSR_MODE_EL1h, except_type_serror); + enter_exception64(vcpu, kvm, PSR_MODE_EL1h, except_type_serror); break; case unpack_vcpu_flag(EXCEPT_AA64_EL2_SYNC): - enter_exception64(vcpu, PSR_MODE_EL2h, except_type_sync); + enter_exception64(vcpu, kvm, PSR_MODE_EL2h, except_type_sync); break; case unpack_vcpu_flag(EXCEPT_AA64_EL2_IRQ): - enter_exception64(vcpu, PSR_MODE_EL2h, except_type_irq); + enter_exception64(vcpu, kvm, PSR_MODE_EL2h, except_type_irq); break; case unpack_vcpu_flag(EXCEPT_AA64_EL2_SERR): - enter_exception64(vcpu, PSR_MODE_EL2h, except_type_serror); + enter_exception64(vcpu, kvm, PSR_MODE_EL2h, except_type_serror); break; default:
@@ -348,10 +348,10 @@ static void kvm_inject_exception(struct kvm_vcpu *vcpu) * Adjust the guest PC (and potentially exception state) depending on * flags provided by the emulation code. */ -void __kvm_adjust_pc(struct kvm_vcpu *vcpu) +void __kvm_adjust_pc_vm(struct kvm_vcpu *vcpu, struct kvm *kvm) { if (vcpu_get_flag(vcpu, PENDING_EXCEPTION)) { - kvm_inject_exception(vcpu); + kvm_inject_exception(vcpu, kvm); vcpu_clear_flag(vcpu, PENDING_EXCEPTION); vcpu_clear_flag(vcpu, EXCEPT_MASK); } else if (vcpu_get_flag(vcpu, INCREMENT_PC)) {
@@ -359,3 +359,8 @@ void __kvm_adjust_pc(struct kvm_vcpu *vcpu) vcpu_clear_flag(vcpu, INCREMENT_PC); } } + +void __kvm_adjust_pc(struct kvm_vcpu *vcpu) +{ + __kvm_adjust_pc_vm(vcpu, kern_hyp_va(vcpu->kvm)); +}
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 2fdb861abb22d..5925d35abba8c 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c@@ -741,11 +741,56 @@ static void handle___pkvm_host_mkyoung_guest(struct kvm_cpu_context *host_ctxt) cpu_reg(host_ctxt, 1) = ret; } +static void adjust_pc_loaded(struct pkvm_hyp_vcpu *hyp_vcpu, + struct kvm_vcpu *host_vcpu) +{ + /* + * PKVM_HOST_STATE_DIRTY names the authoritative copy: the host's + * when set, the hyp vCPU's otherwise. Adjust that one. + */ + if (vcpu_get_flag(host_vcpu, PKVM_HOST_STATE_DIRTY)) { + __kvm_adjust_pc_vm(host_vcpu, hyp_vcpu->vcpu.kvm); + return; + } + + /* Reflect the consumed request back, otherwise it stays pending. */ + vcpu_copy_flag(&hyp_vcpu->vcpu, host_vcpu, PC_UPDATE_REQ); + __kvm_adjust_pc(&hyp_vcpu->vcpu); + vcpu_copy_flag(host_vcpu, &hyp_vcpu->vcpu, PC_UPDATE_REQ); +} + +static void adjust_pc_unloaded(struct kvm_vcpu *host_vcpu) +{ + struct kvm *host_kvm; + + if (!is_protected_kvm_enabled()) { + __kvm_adjust_pc(host_vcpu); + return; + } + + /* The host copy is authoritative, used only while pinned. */ + if (hyp_pin_shared_mem(host_vcpu, host_vcpu + 1)) + return; + + host_kvm = kern_hyp_va(READ_ONCE(host_vcpu->kvm)); + if (!hyp_pin_shared_mem(host_kvm, host_kvm + 1)) { + __kvm_adjust_pc_vm(host_vcpu, host_kvm); + hyp_unpin_shared_mem(host_kvm, host_kvm + 1); + } + hyp_unpin_shared_mem(host_vcpu, host_vcpu + 1); +} + static void handle___kvm_adjust_pc(struct kvm_cpu_context *host_ctxt) { DECLARE_REG(struct kvm_vcpu *, vcpu, host_ctxt, 1); + struct pkvm_hyp_vcpu *hyp_vcpu; + struct kvm_vcpu *host_vcpu; - __kvm_adjust_pc(kern_hyp_va(vcpu)); + host_vcpu = __get_host_hyp_vcpus(vcpu, &hyp_vcpu); + if (!hyp_vcpu) + adjust_pc_unloaded(kern_hyp_va(vcpu)); + else if (!pkvm_hyp_vcpu_is_protected(hyp_vcpu)) + adjust_pc_loaded(hyp_vcpu, host_vcpu); } static void handle___kvm_flush_vm_context(struct kvm_cpu_context *host_ctxt)
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2.39.5