KVM occasionally encounters guests that attempt to access memory outside
the registered RAM memory slots using instructions that don't provide
decoding information in the ESR_EL2 (the ISV bit is not set), and
historically this has led to the kernel printing a confusing error
message in dmesg and returning -ENOYSYS from KVM_RUN.
KVM/Arm now has KVM_CAP_ARM_NISV_TO_USER, which can be enabled from
userspace, and which allows us to handle this with a little bit more
helpful information to the user. For example, we can at least tell the
user if the guest just hit a hole in the guest's memory map, or if this
appeared to be an attempt at doing MMIO.
Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxx>
---
arm/kvm-cpu.c | 20 +++++++++++++++++++-
arm/kvm.c | 8 ++++++++
include/kvm/kvm.h | 1 +
kvm.c | 1 +
mmio.c | 11 +++++++++++
5 files changed, 40 insertions(+), 1 deletion(-)
diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c
index 7780251..25bd3ed 100644
--- a/arm/kvm-cpu.c
+++ b/arm/kvm-cpu.c
@@ -136,7 +136,25 @@ void kvm_cpu__delete(struct kvm_cpu *vcpu)
bool kvm_cpu__handle_exit(struct kvm_cpu *vcpu)
{
- return false;
+ switch (vcpu->kvm_run->exit_reason) {
+ case KVM_EXIT_ARM_NISV: {
+ u64 phys_addr = vcpu->kvm_run->arm_nisv.fault_ipa;
+
+ if (!arm_addr_in_ioport_region(phys_addr) &&
+ !kvm__mmio_exists(vcpu, phys_addr))
+ die("Guest accessed memory outside RAM and IO ranges");
+
+ /*
+ * We cannot fetch and decode instructions from a KVM guest,
+ * which used a load/store instruction that doesn't get
+ * decoded in the ESR towards an I/O device, so we have no
+ * choice but to exit to the user with an error.
+ */
+ die("Guest accessed I/O device with unsupported load/store instruction");
+ }
+ default:
+ return false;
+ }
}
void kvm_cpu__show_page_tables(struct kvm_cpu *vcpu)
diff --git a/arm/kvm.c b/arm/kvm.c
index 1f85fc6..2572ac2 100644
--- a/arm/kvm.c
+++ b/arm/kvm.c
@@ -59,6 +59,8 @@ void kvm__arch_set_cmdline(char *cmdline, bool video)
void kvm__arch_init(struct kvm *kvm, const char *hugetlbfs_path, u64 ram_size)
{
+ struct kvm_enable_cap enable_cap = { .flags = 0 };
+
/*
* Allocate guest memory. We must align our buffer to 64K to
* correlate with the maximum guest page size for virtio-mmio.
@@ -83,6 +85,12 @@ void kvm__arch_init(struct kvm *kvm, const char *hugetlbfs_path, u64 ram_size)
madvise(kvm->arch.ram_alloc_start, kvm->arch.ram_alloc_size,
MADV_HUGEPAGE);
+ if (kvm__supports_extension(kvm, KVM_CAP_ARM_NISV_TO_USER)) {
+ enable_cap.cap = KVM_CAP_ARM_NISV_TO_USER;
+ if (ioctl(kvm->vm_fd, KVM_ENABLE_CAP, &enable_cap) < 0)
+ die("unable to enable NISV_TO_USER capability");
+ }
+
/* Create the virtual GIC. */
if (gic__create(kvm, kvm->cfg.arch.irqchip))
die("Failed to create virtual GIC");
diff --git a/include/kvm/kvm.h b/include/kvm/kvm.h
index 7a73818..05d90ee 100644
--- a/include/kvm/kvm.h
+++ b/include/kvm/kvm.h
@@ -107,6 +107,7 @@ bool kvm__emulate_io(struct kvm_cpu *vcpu, u16 port, void *data, int direction,
bool kvm__emulate_mmio(struct kvm_cpu *vcpu, u64 phys_addr, u8 *data, u32 len, u8 is_write);
int kvm__register_mem(struct kvm *kvm, u64 guest_phys, u64 size, void *userspace_addr,
enum kvm_mem_type type);
+bool kvm__mmio_exists(struct kvm_cpu *vcpu, u64 phys_addr);
static inline int kvm__register_ram(struct kvm *kvm, u64 guest_phys, u64 size,
void *userspace_addr)
{
diff --git a/kvm.c b/kvm.c
index 57c4ff9..03ec43f 100644
--- a/kvm.c
+++ b/kvm.c
@@ -55,6 +55,7 @@ const char *kvm_exit_reasons[] = {
#ifdef CONFIG_PPC64
DEFINE_KVM_EXIT_REASON(KVM_EXIT_PAPR_HCALL),
#endif
+ DEFINE_KVM_EXIT_REASON(KVM_EXIT_ARM_NISV),
};
static int pause_event;
diff --git a/mmio.c b/mmio.c
index 61e1d47..2ab7fa7 100644
--- a/mmio.c
+++ b/mmio.c
@@ -139,3 +139,14 @@ bool kvm__emulate_mmio(struct kvm_cpu *vcpu, u64 phys_addr, u8 *data, u32 len, u
return true;
}
+
+bool kvm__mmio_exists(struct kvm_cpu *vcpu, u64 phys_addr)
+{
+ struct mmio_mapping *mmio;
+
+ br_read_lock(vcpu->kvm);
+ mmio = mmio_search(&mmio_tree, phys_addr, 1);
+ br_read_unlock(vcpu->kvm);
+
+ return mmio != NULL;
+}
--
2.17.1
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