kvm: Don't crash debug dump if address isn't in guest memory

We don't do MMU translation in the hypevisor for guest memory addresses which
causes us to try to dereference invalid pointers.  Work around the problem by
checking that a pointer is in guest memory before dumping the contents.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

diff --git a/tools/kvm/kvm.c b/tools/kvm/kvm.c
index 64316875db874e7e8cb7926d3ae7c5496ab954af..11dec87ef0e5093b515e3299a1c807f483e494fb 100644 (file)
--- a/tools/kvm/kvm.c
+++ b/tools/kvm/kvm.c
@@ -50,6 +50,11 @@ const char *kvm_exit_reasons[] = {
        DEFINE_KVM_EXIT_REASON(KVM_EXIT_INTERNAL_ERROR),
 };
 
+static inline bool host_ptr_in_ram(struct kvm *self, void *p)
+{
+       return self->ram_start <= p && p < (self->ram_start + self->ram_size);
+}
+
 static inline uint32_t segment_to_flat(uint16_t selector, uint16_t offset)
 {
        return ((uint32_t)selector << 4) + (uint32_t) offset;
@@ -650,6 +655,9 @@ void kvm__show_code(struct kvm *self)
        printf("Code: ");
 
        for (i = 0; i < code_len; i++, ip++) {
+               if (!host_ptr_in_ram(self, ip))
+                       break;
+
                c = *ip;
 
                if (ip == guest_flat_to_host(self, ip_to_flat(self, self->regs.rip)))
@@ -678,9 +686,20 @@ void kvm__show_page_tables(struct kvm *self)
                die("KVM_GET_SREGS failed");
 
        pte4    = guest_flat_to_host(self, self->sregs.cr3);
+       if (!host_ptr_in_ram(self, pte4))
+               return;
+
        pte3    = guest_flat_to_host(self, (*pte4 & ~0xfff));
+       if (!host_ptr_in_ram(self, pte3))
+               return;
+
        pte2    = guest_flat_to_host(self, (*pte3 & ~0xfff));
+       if (!host_ptr_in_ram(self, pte2))
+               return;
+
        pte1    = guest_flat_to_host(self, (*pte2 & ~0xfff));
+       if (!host_ptr_in_ram(self, pte1))
+               return;
 
        printf("Page Tables:\n");
        if (*pte2 & (1 << 7))
@@ -700,8 +719,12 @@ void kvm__dump_mem(struct kvm *self, unsigned long addr, unsigned long size)
 
        p = guest_flat_to_host(self, addr);
 
-       for (n = 0; n < size; n+=8)
+       for (n = 0; n < size; n+=8) {
+               if (!host_ptr_in_ram(self, p + n))
+                       break;
+
                printf("  0x%08lx: %02x %02x %02x %02x  %02x %02x %02x %02x\n",
                        addr + n, p[n + 0], p[n + 1], p[n + 2], p[n + 3],
                                  p[n + 4], p[n + 5], p[n + 6], p[n + 7]);
+       }
 }