[PATCH] Check for ambiguities in create alias ioctl.

Glauber Costa
2008-11-18T01:05:11Z

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/ia64/kvm/kvm-ia64.c | 6 ++++++
arch/powerpc/kvm/powerpc.c | 5 +++++
arch/s390/kvm/kvm-s390.c | 6 ++++++
arch/x86/kvm/x86.c | 23 +++++++++++++++++++++--
include/linux/kvm_host.h | 4 ++++
virt/kvm/kvm_main.c | 31 ++++++++++++++++++++-----------
6 files changed, 62 insertions(+), 13 deletions(-)

diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index af1464f..7e9d796 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -1695,6 +1695,12 @@ void kvm_arch_hardware_unsetup(void)
{
}

+int kvm_arch_check_overlap(struct kvm *kvm, gfn_t base_gfn,
+ unsigned long npages, void *me)
+{
+ return 0;
+}
+
static void vcpu_kick_intr(void *info)
{
#ifdef DEBUG
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 90a6fc4..a0c164e 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -45,6 +45,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
return !(v->arch.msr & MSR_WE);
}

+int kvm_arch_check_overlap(struct kvm *kvm, gfn_t base_gfn,
+ unsigned long npages, void *me)
+{
+ return 0;
+}

int kvmppc_emulate_mmio(struct kvm_run *run, struct kvm_vcpu *vcpu)
{
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 8b00eb2..780f33e 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -101,6 +101,12 @@ void kvm_arch_exit(void)
{
}

+int kvm_arch_check_overlap(struct kvm *kvm, gfn_t base_gfn,
+ unsigned long npages, void *me)
+{
+ return 0;
+}
+
/* Section: device related */
long kvm_arch_dev_ioctl(struct file *filp,
unsigned int ioctl, unsigned long arg)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f1f8ff2..324af5e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1506,6 +1506,22 @@ gfn_t unalias_gfn(struct kvm *kvm, gfn_t gfn)
return gfn;
}

+int kvm_arch_check_overlap(struct kvm *kvm, gfn_t base_gfn,
+ unsigned long npages, void *me)
+{
+ int i;
+ for (i = 0; i < kvm->arch.naliases ; i++) {
+ struct kvm_mem_alias *p = &kvm->arch.aliases[i];
+ if (p == me)
+ continue;
+
+ if (!((base_gfn + npages < p->base_gfn) ||
+ (base_gfn > p->base_gfn + p->npages)))
+ return -EEXIST;
+ }
+ return 0;
+}
+
/*
* Set a new alias region. Aliases map a portion of physical memory into
* another portion. This is useful for memory windows, for example the PC
@@ -1540,18 +1556,21 @@ static int kvm_vm_ioctl_set_memory_alias(struct kvm *kvm,
p->npages = alias->memory_size >> PAGE_SHIFT;
p->target_gfn = alias->target_phys_addr >> PAGE_SHIFT;

+ r = kvm_check_overlap(kvm, p->base_gfn, p->npages, p);
+ if (r)
+ goto out_locked;
+
for (n = KVM_ALIAS_SLOTS; n > 0; --n)
if (kvm->arch.aliases[n - 1].npages)
break;
kvm->arch.naliases = n;

+out_locked:
spin_unlock(&kvm->mmu_lock);
kvm_mmu_zap_all(kvm);

up_write(&kvm->slots_lock);

- return 0;
-
out:
return r;
}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index bb92be2..79f34ab 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -178,6 +178,10 @@ int kvm_arch_set_memory_region(struct kvm *kvm,
struct kvm_userspace_memory_region *mem,
struct kvm_memory_slot old,
int user_alloc);
+int kvm_check_overlap(struct kvm *kvm, gfn_t base_gfn,
+ unsigned long pages, void *me);
+int kvm_arch_check_overlap(struct kvm *kvm, gfn_t base_gfn,
+ unsigned long pages, void *me);
void kvm_arch_flush_shadow(struct kvm *kvm);
gfn_t unalias_gfn(struct kvm *kvm, gfn_t gfn);
struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fd265b2..18af322 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -685,6 +685,23 @@ static int kvm_vm_release(struct inode *inode, struct file *filp)
return 0;
}

+int kvm_check_overlap(struct kvm *kvm, gfn_t base_gfn,
+ unsigned long npages, void *me)
+{
+ int i;
+
+ for (i = 0; i < KVM_MEMORY_SLOTS; ++i) {
+ struct kvm_memory_slot *s = &kvm->memslots[i];
+
+ if (s == me)
+ continue;
+ if (!((base_gfn + npages <= s->base_gfn) ||
+ (base_gfn >= s->base_gfn + s->npages)))
+ return -EEXIST;
+ }
+ return kvm_arch_check_overlap(kvm, base_gfn, npages, me);
+}
+
/*
* Allocate some memory and give it an address in the guest physical address
* space.
@@ -700,7 +717,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
int r;
gfn_t base_gfn;
unsigned long npages;
- unsigned long i;
struct kvm_memory_slot *memslot;
struct kvm_memory_slot old, new;

@@ -733,17 +749,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
if (npages && old.npages && npages != old.npages)
goto out_free;

- /* Check for overlaps */
- r = -EEXIST;
- for (i = 0; i < KVM_MEMORY_SLOTS; ++i) {
- struct kvm_memory_slot *s = &kvm->memslots[i];
+ r = kvm_check_overlap(kvm, base_gfn, npages, memslot);
+ if (r)
+ goto out_free;

- if (s == memslot)
- continue;
- if (!((base_gfn + npages <= s->base_gfn) ||
- (base_gfn >= s->base_gfn + s->npages)))
- goto out_free;
- }

/* Free page dirty bitmap if unneeded */
if (!(new.flags & KVM_MEM_LOG_DIRTY_PAGES))
--
1.5.6.5