[PATCH] Check for ambiguities in create alias ioctl.

Glauber Costa
2008-11-13T12:36:33Z

The current alias ioctl allows for the creation of
an alias covering a gpa that already exists. It is invalid,
because the gpa space needs to be uniquely mapped. So, if
there's a memory slot covering gpa range 0x123000 to 0x124000,
and we create an alias from any gpa within that range to a different
target, we create an essential ambiguity that brings no value at
the cost of a lot of confusion. Right now this confusion
manifests itself as a BUG() triggered in the rmaps code path.

Signed-off-by: Glauber Costa <glommer@redhat.com>
---
arch/x86/kvm/x86.c | 12 ++++++++++--
1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7a2aeba..c3b5770 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1591,6 +1591,8 @@ static int kvm_vm_ioctl_set_memory_alias(struct kvm *kvm,
{
int r, n;
struct kvm_mem_alias *p;
+ gfn_t base_gfn;
+ unsigned long npages;

r = -EINVAL;
/* General sanity checks */
@@ -1607,12 +1609,18 @@ static int kvm_vm_ioctl_set_memory_alias(struct kvm *kvm,
< alias->target_phys_addr)
goto out;

+ base_gfn = alias->guest_phys_addr >> PAGE_SHIFT;
+ npages = alias->memory_size >> PAGE_SHIFT;
+
+ if (gfn_to_memslot(kvm, base_gfn) || gfn_to_memslot(kvm, base_gfn + npages))
+ goto out;
+
down_write(&kvm->slots_lock);
spin_lock(&kvm->mmu_lock);

p = &kvm->arch.aliases[alias->slot];
- p->base_gfn = alias->guest_phys_addr >> PAGE_SHIFT;
- p->npages = alias->memory_size >> PAGE_SHIFT;
+ p->base_gfn = base_gfn;
+ p->npages = npages;
p->target_gfn = alias->target_phys_addr >> PAGE_SHIFT;

for (n = KVM_ALIAS_SLOTS; n > 0; --n)
--
1.5.6.5