KVM: Add helpers to wrap vcpu->srcu_idx and yell if it's abused

Add wrappers to acquire/release KVM's SRCU lock when stashing the index
in vcpu->src_idx, along with rudimentary detection of illegal usage,
e.g. re-acquiring SRCU and thus overwriting vcpu->src_idx.  Because the
SRCU index is (currently) either 0 or 1, illegal nesting bugs can go
unnoticed for quite some time and only cause problems when the nested
lock happens to get a different index.

Wrap the WARNs in PROVE_RCU=y, and make them ONCE, otherwise KVM will
likely yell so loudly that it will bring the kernel to its knees.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Fabiano Rosas <farosas@linux.ibm.com>
Message-Id: <20220415004343.2203171-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

11 files changed, 71 insertions, 50 deletions

diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index e4ce2a35483f..42851c32ff3b 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -168,9 +168,10 @@ int kvmppc_mmu_walk_radix_tree(struct kvm_vcpu *vcpu, gva_t eaddr,
 			return -EINVAL;
 		/* Read the entry from guest memory */
 		addr = base + (index * sizeof(rpte));
-		vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
+
+		kvm_vcpu_srcu_read_lock(vcpu);
 		ret = kvm_read_guest(kvm, addr, &rpte, sizeof(rpte));
-		srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
+		kvm_vcpu_srcu_read_unlock(vcpu);
 		if (ret) {
 			if (pte_ret_p)
 				*pte_ret_p = addr;
@@ -246,9 +247,9 @@ int kvmppc_mmu_radix_translate_table(struct kvm_vcpu *vcpu, gva_t eaddr,
 
 	/* Read the table to find the root of the radix tree */
 	ptbl = (table & PRTB_MASK) + (table_index * sizeof(entry));
-	vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
+	kvm_vcpu_srcu_read_lock(vcpu);
 	ret = kvm_read_guest(kvm, ptbl, &entry, sizeof(entry));
-	srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
+	kvm_vcpu_srcu_read_unlock(vcpu);
 	if (ret)
 		return ret;
 
diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
index 9d373f8963ee..c943a051c6e7 100644
--- a/arch/powerpc/kvm/book3s_hv_nested.c
+++ b/arch/powerpc/kvm/book3s_hv_nested.c
@@ -306,10 +306,10 @@ long kvmhv_enter_nested_guest(struct kvm_vcpu *vcpu)
 	/* copy parameters in */
 	hv_ptr = kvmppc_get_gpr(vcpu, 4);
 	regs_ptr = kvmppc_get_gpr(vcpu, 5);
-	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+	kvm_vcpu_srcu_read_lock(vcpu);
 	err = kvmhv_read_guest_state_and_regs(vcpu, &l2_hv, &l2_regs,
 					      hv_ptr, regs_ptr);
-	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+	kvm_vcpu_srcu_read_unlock(vcpu);
 	if (err)
 		return H_PARAMETER;
 
@@ -410,10 +410,10 @@ long kvmhv_enter_nested_guest(struct kvm_vcpu *vcpu)
 		byteswap_hv_regs(&l2_hv);
 		byteswap_pt_regs(&l2_regs);
 	}
-	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+	kvm_vcpu_srcu_read_lock(vcpu);
 	err = kvmhv_write_guest_state_and_regs(vcpu, &l2_hv, &l2_regs,
 					       hv_ptr, regs_ptr);
-	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+	kvm_vcpu_srcu_read_unlock(vcpu);
 	if (err)
 		return H_AUTHORITY;
 
@@ -600,16 +600,16 @@ long kvmhv_copy_tofrom_guest_nested(struct kvm_vcpu *vcpu)
 			goto not_found;
 
 		/* Write what was loaded into our buffer back to the L1 guest */
-		vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+		kvm_vcpu_srcu_read_lock(vcpu);
 		rc = kvm_vcpu_write_guest(vcpu, gp_to, buf, n);
-		srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+		kvm_vcpu_srcu_read_unlock(vcpu);
 		if (rc)
 			goto not_found;
 	} else {
 		/* Load the data to be stored from the L1 guest into our buf */
-		vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+		kvm_vcpu_srcu_read_lock(vcpu);
 		rc = kvm_vcpu_read_guest(vcpu, gp_from, buf, n);
-		srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+		kvm_vcpu_srcu_read_unlock(vcpu);
 		if (rc)
 			goto not_found;
 
diff --git a/arch/powerpc/kvm/book3s_rtas.c b/arch/powerpc/kvm/book3s_rtas.c
index 0f847f1e5ddd..6808bda0dbc1 100644
--- a/arch/powerpc/kvm/book3s_rtas.c
+++ b/arch/powerpc/kvm/book3s_rtas.c
@@ -229,9 +229,9 @@ int kvmppc_rtas_hcall(struct kvm_vcpu *vcpu)
 	 */
 	args_phys = kvmppc_get_gpr(vcpu, 4) & KVM_PAM;
 
-	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+	kvm_vcpu_srcu_read_lock(vcpu);
 	rc = kvm_read_guest(vcpu->kvm, args_phys, &args, sizeof(args));
-	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+	kvm_vcpu_srcu_read_unlock(vcpu);
 	if (rc)
 		goto fail;
 
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 875c30c12db0..533c4232e5ab 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -425,9 +425,9 @@ int kvmppc_ld(struct kvm_vcpu *vcpu, ulong *eaddr, int size, void *ptr,
 		return EMULATE_DONE;
 	}
 
-	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+	kvm_vcpu_srcu_read_lock(vcpu);
 	rc = kvm_read_guest(vcpu->kvm, pte.raddr, ptr, size);
-	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+	kvm_vcpu_srcu_read_unlock(vcpu);
 	if (rc)
 		return EMULATE_DO_MMIO;
 
diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index 4a52fda6417b..7461f964d20a 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -727,13 +727,13 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 	/* Mark this VCPU ran at least once */
 	vcpu->arch.ran_atleast_once = true;
 
-	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+	kvm_vcpu_srcu_read_lock(vcpu);
 
 	/* Process MMIO value returned from user-space */
 	if (run->exit_reason == KVM_EXIT_MMIO) {
 		ret = kvm_riscv_vcpu_mmio_return(vcpu, vcpu->run);
 		if (ret) {
-			srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+			kvm_vcpu_srcu_read_unlock(vcpu);
 			return ret;
 		}
 	}
@@ -742,13 +742,13 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 	if (run->exit_reason == KVM_EXIT_RISCV_SBI) {
 		ret = kvm_riscv_vcpu_sbi_return(vcpu, vcpu->run);
 		if (ret) {
-			srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+			kvm_vcpu_srcu_read_unlock(vcpu);
 			return ret;
 		}
 	}
 
 	if (run->immediate_exit) {
-		srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+		kvm_vcpu_srcu_read_unlock(vcpu);
 		return -EINTR;
 	}
 
@@ -787,7 +787,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 		 */
 		vcpu->mode = IN_GUEST_MODE;
 
-		srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+		kvm_vcpu_srcu_read_unlock(vcpu);
 		smp_mb__after_srcu_read_unlock();
 
 		/*
@@ -805,7 +805,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 			vcpu->mode = OUTSIDE_GUEST_MODE;
 			local_irq_enable();
 			preempt_enable();
-			vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+			kvm_vcpu_srcu_read_lock(vcpu);
 			continue;
 		}
 
@@ -849,7 +849,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 
 		preempt_enable();
 
-		vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+		kvm_vcpu_srcu_read_lock(vcpu);
 
 		ret = kvm_riscv_vcpu_exit(vcpu, run, &trap);
 	}
@@ -858,7 +858,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 
 	vcpu_put(vcpu);
 
-	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+	kvm_vcpu_srcu_read_unlock(vcpu);
 
 	return ret;
 }
diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c
index 2d56faddb9d1..a72c15d4b42a 100644
--- a/arch/riscv/kvm/vcpu_exit.c
+++ b/arch/riscv/kvm/vcpu_exit.c
@@ -456,9 +456,9 @@ static int stage2_page_fault(struct kvm_vcpu *vcpu, struct kvm_run *run,
 void kvm_riscv_vcpu_wfi(struct kvm_vcpu *vcpu)
 {
 	if (!kvm_arch_vcpu_runnable(vcpu)) {
-		srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+		kvm_vcpu_srcu_read_unlock(vcpu);
 		kvm_vcpu_halt(vcpu);
-		vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+		kvm_vcpu_srcu_read_lock(vcpu);
 		kvm_clear_request(KVM_REQ_UNHALT, vcpu);
 	}
 }
diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 9b30beac904d..af96dc0549a4 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -1334,11 +1334,11 @@ int kvm_s390_handle_wait(struct kvm_vcpu *vcpu)
 	hrtimer_start(&vcpu->arch.ckc_timer, sltime, HRTIMER_MODE_REL);
 	VCPU_EVENT(vcpu, 4, "enabled wait: %llu ns", sltime);
 no_timer:
-	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+	kvm_vcpu_srcu_read_unlock(vcpu);
 	kvm_vcpu_halt(vcpu);
 	vcpu->valid_wakeup = false;
 	__unset_cpu_idle(vcpu);
-	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+	kvm_vcpu_srcu_read_lock(vcpu);
 
 	hrtimer_cancel(&vcpu->arch.ckc_timer);
 	return 0;
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 156d1c25a3c1..da3dabda1a12 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -4237,14 +4237,14 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 	 * We try to hold kvm->srcu during most of vcpu_run (except when run-
 	 * ning the guest), so that memslots (and other stuff) are protected
 	 */
-	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+	kvm_vcpu_srcu_read_lock(vcpu);
 
 	do {
 		rc = vcpu_pre_run(vcpu);
 		if (rc)
 			break;
 
-		srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+		kvm_vcpu_srcu_read_unlock(vcpu);
 		/*
 		 * As PF_VCPU will be used in fault handler, between
 		 * guest_enter and guest_exit should be no uaccess.
@@ -4281,12 +4281,12 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 		__enable_cpu_timer_accounting(vcpu);
 		guest_exit_irqoff();
 		local_irq_enable();
-		vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+		kvm_vcpu_srcu_read_lock(vcpu);
 
 		rc = vcpu_post_run(vcpu, exit_reason);
 	} while (!signal_pending(current) && !guestdbg_exit_pending(vcpu) && !rc);
 
-	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+	kvm_vcpu_srcu_read_unlock(vcpu);
 	return rc;
 }
 
diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index acda4b6fc851..dada78b92691 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -1091,7 +1091,7 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 
 	handle_last_fault(vcpu, vsie_page);
 
-	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+	kvm_vcpu_srcu_read_unlock(vcpu);
 
 	/* save current guest state of bp isolation override */
 	guest_bp_isolation = test_thread_flag(TIF_ISOLATE_BP_GUEST);
@@ -1133,7 +1133,7 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 	if (!guest_bp_isolation)
 		clear_thread_flag(TIF_ISOLATE_BP_GUEST);
 
-	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+	kvm_vcpu_srcu_read_lock(vcpu);
 
 	if (rc == -EINTR) {
 		VCPU_EVENT(vcpu, 3, "%s", "machine check");
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 867c0fd8d187..51eb27824452 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10097,7 +10097,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	/* Store vcpu->apicv_active before vcpu->mode.  */
 	smp_store_release(&vcpu->mode, IN_GUEST_MODE);
 
-	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+	kvm_vcpu_srcu_read_unlock(vcpu);
 
 	/*
 	 * 1) We should set ->mode before checking ->requests.  Please see
@@ -10128,7 +10128,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		smp_wmb();
 		local_irq_enable();
 		preempt_enable();
-		vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+		kvm_vcpu_srcu_read_lock(vcpu);
 		r = 1;
 		goto cancel_injection;
 	}
@@ -10254,7 +10254,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	local_irq_enable();
 	preempt_enable();
 
-	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+	kvm_vcpu_srcu_read_lock(vcpu);
 
 	/*
 	 * Profile KVM exit RIPs:
@@ -10284,7 +10284,7 @@ out:
 }
 
 /* Called within kvm->srcu read side.  */
-static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
+static inline int vcpu_block(struct kvm_vcpu *vcpu)
 {
 	bool hv_timer;
 
@@ -10300,12 +10300,12 @@ static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
 		if (hv_timer)
 			kvm_lapic_switch_to_sw_timer(vcpu);
 
-		srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
+		kvm_vcpu_srcu_read_unlock(vcpu);
 		if (vcpu->arch.mp_state == KVM_MP_STATE_HALTED)
 			kvm_vcpu_halt(vcpu);
 		else
 			kvm_vcpu_block(vcpu);
-		vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
+		kvm_vcpu_srcu_read_lock(vcpu);
 
 		if (hv_timer)
 			kvm_lapic_switch_to_hv_timer(vcpu);
@@ -10347,7 +10347,6 @@ static inline bool kvm_vcpu_running(struct kvm_vcpu *vcpu)
 static int vcpu_run(struct kvm_vcpu *vcpu)
 {
 	int r;
-	struct kvm *kvm = vcpu->kvm;
 
 	vcpu->arch.l1tf_flush_l1d = true;
 
@@ -10355,7 +10354,7 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
 		if (kvm_vcpu_running(vcpu)) {
 			r = vcpu_enter_guest(vcpu);
 		} else {
-			r = vcpu_block(kvm, vcpu);
+			r = vcpu_block(vcpu);
 		}
 
 		if (r <= 0)
@@ -10374,9 +10373,9 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
 		}
 
 		if (__xfer_to_guest_mode_work_pending()) {
-			srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
+			kvm_vcpu_srcu_read_unlock(vcpu);
 			r = xfer_to_guest_mode_handle_work(vcpu);
-			vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
+			kvm_vcpu_srcu_read_lock(vcpu);
 			if (r)
 				return r;
 		}
@@ -10479,7 +10478,6 @@ static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
 int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 {
 	struct kvm_run *kvm_run = vcpu->run;
-	struct kvm *kvm = vcpu->kvm;
 	int r;
 
 	vcpu_load(vcpu);
@@ -10487,7 +10485,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 	kvm_run->flags = 0;
 	kvm_load_guest_fpu(vcpu);
 
-	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+	kvm_vcpu_srcu_read_lock(vcpu);
 	if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) {
 		if (kvm_run->immediate_exit) {
 			r = -EINTR;
@@ -10499,9 +10497,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 		 */
 		WARN_ON_ONCE(kvm_lapic_hv_timer_in_use(vcpu));
 
-		srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
+		kvm_vcpu_srcu_read_unlock(vcpu);
 		kvm_vcpu_block(vcpu);
-		vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
+		kvm_vcpu_srcu_read_lock(vcpu);
 
 		if (kvm_apic_accept_events(vcpu) < 0) {
 			r = 0;
@@ -10562,7 +10560,7 @@ out:
 	if (kvm_run->kvm_valid_regs)
 		store_regs(vcpu);
 	post_kvm_run_save(vcpu);
-	srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
+	kvm_vcpu_srcu_read_unlock(vcpu);
 
 	kvm_sigset_deactivate(vcpu);
 	vcpu_put(vcpu);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 3f9b22c4983a..2dab4b696682 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -315,7 +315,10 @@ struct kvm_vcpu {
 	int cpu;
 	int vcpu_id; /* id given by userspace at creation */
 	int vcpu_idx; /* index in kvm->vcpus array */
-	int srcu_idx;
+	int ____srcu_idx; /* Don't use this directly.  You've been warned. */
+#ifdef CONFIG_PROVE_RCU
+	int srcu_depth;
+#endif
 	int mode;
 	u64 requests;
 	unsigned long guest_debug;
@@ -840,6 +843,25 @@ static inline void kvm_vm_bugged(struct kvm *kvm)
 	unlikely(__ret);					\
 })
 
+static inline void kvm_vcpu_srcu_read_lock(struct kvm_vcpu *vcpu)
+{
+#ifdef CONFIG_PROVE_RCU
+	WARN_ONCE(vcpu->srcu_depth++,
+		  "KVM: Illegal vCPU srcu_idx LOCK, depth=%d", vcpu->srcu_depth - 1);
+#endif
+	vcpu->____srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+}
+
+static inline void kvm_vcpu_srcu_read_unlock(struct kvm_vcpu *vcpu)
+{
+	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->____srcu_idx);
+
+#ifdef CONFIG_PROVE_RCU
+	WARN_ONCE(--vcpu->srcu_depth,
+		  "KVM: Illegal vCPU srcu_idx UNLOCK, depth=%d", vcpu->srcu_depth);
+#endif
+}
+
 static inline bool kvm_dirty_log_manual_protect_and_init_set(struct kvm *kvm)
 {
 	return !!(kvm->manual_dirty_log_protect & KVM_DIRTY_LOG_INITIALLY_SET);