KVM: arm/arm64: VGIC/ITS: protect kvm_read_guest() calls with SRCU lock

kvm_read_guest() will eventually look up in kvm_memslots(), which requires
either to hold the kvm->slots_lock or to be inside a kvm->srcu critical
section.
In contrast to x86 and s390 we don't take the SRCU lock on every guest
exit, so we have to do it individually for each kvm_read_guest() call.

Provide a wrapper which does that and use that everywhere.

Note that ending the SRCU critical section before returning from the
kvm_read_guest() wrapper is safe, because the data has been *copied*, so
we don't need to rely on valid references to the memslot anymore.

Cc: Stable <stable@vger.kernel.org> # 4.8+
Reported-by: Jan Glauber <jan.glauber@caviumnetworks.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
index 707a1f06dc5d5e207f0d2c18e0b37844569ca199..f675162663f09a054253b8ad6d86361c74968618 100644 (file)
--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h
@@ -309,6 +309,22 @@ static inline unsigned int kvm_get_vmid_bits(void)
        return 8;
 }
 
+/*
+ * We are not in the kvm->srcu critical section most of the time, so we take
+ * the SRCU read lock here. Since we copy the data from the user page, we
+ * can immediately drop the lock again.
+ */
+static inline int kvm_read_guest_lock(struct kvm *kvm,
+                                     gpa_t gpa, void *data, unsigned long len)
+{
+       int srcu_idx = srcu_read_lock(&kvm->srcu);
+       int ret = kvm_read_guest(kvm, gpa, data, len);
+
+       srcu_read_unlock(&kvm->srcu, srcu_idx);
+
+       return ret;
+}
+
 static inline void *kvm_get_hyp_vector(void)
 {
        return kvm_ksym_ref(__kvm_hyp_vector);

diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 082110993647b9b7e30cf18da5d9d447c58d362f..6128992c2ded6b7e1aa4ba835474f6f45f6fdc5e 100644 (file)
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -360,6 +360,22 @@ static inline unsigned int kvm_get_vmid_bits(void)
        return (cpuid_feature_extract_unsigned_field(reg, ID_AA64MMFR1_VMIDBITS_SHIFT) == 2) ? 16 : 8;
 }
 
+/*
+ * We are not in the kvm->srcu critical section most of the time, so we take
+ * the SRCU read lock here. Since we copy the data from the user page, we
+ * can immediately drop the lock again.
+ */
+static inline int kvm_read_guest_lock(struct kvm *kvm,
+                                     gpa_t gpa, void *data, unsigned long len)
+{
+       int srcu_idx = srcu_read_lock(&kvm->srcu);
+       int ret = kvm_read_guest(kvm, gpa, data, len);
+
+       srcu_read_unlock(&kvm->srcu, srcu_idx);
+
+       return ret;
+}
+
 #ifdef CONFIG_KVM_INDIRECT_VECTORS
 /*
  * EL2 vectors can be mapped and rerouted in a number of ways,

diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
index 51a80b6006326ae44eb48080db96ae502c02794a..7cb060e01a76fee3301a97dc89062a44aa46f261 100644 (file)
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -281,8 +281,8 @@ static int update_lpi_config(struct kvm *kvm, struct vgic_irq *irq,
        int ret;
        unsigned long flags;
 
-       ret = kvm_read_guest(kvm, propbase + irq->intid - GIC_LPI_OFFSET,
-                            &prop, 1);
+       ret = kvm_read_guest_lock(kvm, propbase + irq->intid - GIC_LPI_OFFSET,
+                                 &prop, 1);
 
        if (ret)
                return ret;
@@ -444,8 +444,9 @@ static int its_sync_lpi_pending_table(struct kvm_vcpu *vcpu)
                 * this very same byte in the last iteration. Reuse that.
                 */
                if (byte_offset != last_byte_offset) {
-                       ret = kvm_read_guest(vcpu->kvm, pendbase + byte_offset,
-                                            &pendmask, 1);
+                       ret = kvm_read_guest_lock(vcpu->kvm,
+                                                 pendbase + byte_offset,
+                                                 &pendmask, 1);
                        if (ret) {
                                kfree(intids);
                                return ret;
@@ -789,7 +790,7 @@ static bool vgic_its_check_id(struct vgic_its *its, u64 baser, u32 id,
                return false;
 
        /* Each 1st level entry is represented by a 64-bit value. */
-       if (kvm_read_guest(its->dev->kvm,
+       if (kvm_read_guest_lock(its->dev->kvm,
                           BASER_ADDRESS(baser) + index * sizeof(indirect_ptr),
                           &indirect_ptr, sizeof(indirect_ptr)))
                return false;
@@ -1370,8 +1371,8 @@ static void vgic_its_process_commands(struct kvm *kvm, struct vgic_its *its)
        cbaser = CBASER_ADDRESS(its->cbaser);
 
        while (its->cwriter != its->creadr) {
-               int ret = kvm_read_guest(kvm, cbaser + its->creadr,
-                                        cmd_buf, ITS_CMD_SIZE);
+               int ret = kvm_read_guest_lock(kvm, cbaser + its->creadr,
+                                             cmd_buf, ITS_CMD_SIZE);
                /*
                 * If kvm_read_guest() fails, this could be due to the guest
                 * programming a bogus value in CBASER or something else going