[patch] kvm: make cr3 loading more robust

Ingo Molnar
2007-01-03T02:10:57Z

From: Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>
Subject: [patch] kvm: make cr3 loading more robust

rmap_write_protect() has a BUG_ON() if a physical address is not found
the the memslot. But this is a possible scenario if a buggy guest OS
loads an invalid or corrupted cr3 value. So exit more gracefully.

[ Avi: this patch needs kvm_mmu_get_page() NULL return to not be ignored
by mmu_alloc_roots()/nonpaging_init_context()/paging_new_cr3()/etc.
and passed further down - i assume you are working on those
issues already, or should i fix those too? ]

Signed-off-by: Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>

Index: linux/drivers/kvm/mmu.c
===================================================================
--- linux.orig/drivers/kvm/mmu.c
+++ linux/drivers/kvm/mmu.c
@@ -378,7 +378,7 @@ static void rmap_remove(struct kvm_vcpu
}
}

-static void rmap_write_protect(struct kvm_vcpu *vcpu, u64 gfn)
+static int rmap_write_protect(struct kvm_vcpu *vcpu, u64 gfn)
{
struct kvm *kvm = vcpu->kvm;
struct page *page;
@@ -387,7 +387,8 @@ static void rmap_write_protect(struct kv
u64 *spte;

slot = gfn_to_memslot(kvm, gfn);
- BUG_ON(!slot);
+ if (!slot)
+ return -1;
page = gfn_to_page(slot, gfn);

while (page->private) {
@@ -407,6 +408,7 @@ static void rmap_write_protect(struct kv
kvm_arch_ops->tlb_flush(vcpu);
*spte &= ~(u64)PT_WRITABLE_MASK;
}
+ return 0;
}

static int is_empty_shadow_page(hpa_t page_hpa)
@@ -592,12 +594,17 @@ static struct kvm_mmu_page *kvm_mmu_get_
page = kvm_mmu_alloc_page(vcpu, parent_pte);
if (!page)
return page;
+ if (!metaphysical) {
+ if (rmap_write_protect(vcpu, gfn) < 0) {
+ kvm_mmu_free_page(vcpu, page->page_hpa);
+ return NULL;
+ }
+ }
pgprintk("%s: adding gfn %lx role %x\n", __FUNCTION__, gfn, role.word);
page->gfn = gfn;
page->role = role;
hlist_add_head(&page->hash_link, bucket);
- if (!metaphysical)
- rmap_write_protect(vcpu, gfn);
+
return page;
}