[PATCH 3/3] KVM: Add helpers to wrap vcpu->srcu_idx and yell if it's abused

Sean Christopherson
2022-04-15T00:44:05Z

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>
---
arch/powerpc/kvm/book3s_64_mmu_radix.c | 9 +++++----
arch/powerpc/kvm/book3s_hv_nested.c | 16 +++++++--------
arch/powerpc/kvm/book3s_rtas.c | 4 ++--
arch/powerpc/kvm/powerpc.c | 4 ++--
arch/riscv/kvm/vcpu.c | 16 +++++++--------
arch/riscv/kvm/vcpu_exit.c | 4 ++--
arch/s390/kvm/interrupt.c | 4 ++--
arch/s390/kvm/kvm-s390.c | 8 ++++----
arch/s390/kvm/vsie.c | 4 ++--
arch/x86/kvm/x86.c | 28 ++++++++++++--------------
include/linux/kvm_host.h | 24 +++++++++++++++++++++-
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 9772b176e406..fd88c2412e83 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 2f1caf23eed4..256cf04ec01e 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -724,13 +724,13 @@ 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;
}
}
@@ -739,13 +739,13 @@ 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;
}

@@ -784,7 +784,7 @@ 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();

/*
@@ -802,7 +802,7 @@ 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;
}

@@ -846,7 +846,7 @@ 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);
}
@@ -855,7 +855,7 @@ 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 f35fe09de59d..bc24b35c4e80 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10157,7 +10157,7 @@ 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
@@ -10188,7 +10188,7 @@ 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;
}
@@ -10314,7 +10314,7 @@ 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:
@@ -10344,7 +10344,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
}

/* 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;

@@ -10360,12 +10360,12 @@ 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);
@@ -10407,7 +10407,6 @@ 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;

@@ -10415,7 +10414,7 @@ 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)
@@ -10437,9 +10436,9 @@ 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;
}
@@ -10542,7 +10541,6 @@ 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);
@@ -10550,7 +10548,7 @@ 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;
@@ -10562,9 +10560,9 @@ 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;
@@ -10625,7 +10623,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
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 252ee4a61b58..76fc7233bd6a 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;
@@ -841,6 +844,25 @@ 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);
--
2.36.0.rc0.470.gd361397f0d-goog