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KVM: Clean up __kvm_gfn_to_hva_cache_init() and its callers 

Barret reported a (technically benign) bug where nr_pages_avail can be
accessed without being initialized if gfn_to_hva_many() fails.

  virt/kvm/kvm_main.c:2193:13: warning: 'nr_pages_avail' may be
  used uninitialized in this function [-Wmaybe-uninitialized]

Rather than simply squashing the warning by initializing nr_pages_avail,
fix the underlying issues by reworking __kvm_gfn_to_hva_cache_init() to
return immediately instead of continuing on.  Now that all callers check
the result and/or bail immediately on a bad hva, there's no need to
explicitly nullify the memslot on error.

Reported-by: Barret Rhoden <brho@google.com>
Fixes: f1b9dd5eb8 ("kvm: Disallow wraparound in kvm_gfn_to_hva_cache_init")
Cc: Jim Mattson <jmattson@google.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2020-01-09 14:58:55 -05:00 committed by Paolo Bonzini
parent fcfbc61754
commit 6ad1e29fe0
1 changed files with 12 additions and 9 deletions
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19
virt/kvm/kvm_main.c
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@ -2130,33 +2130,36 @@ static int __kvm_gfn_to_hva_cache_init(struct kvm_memslots *slots,
gfn_t end_gfn = (gpa + len - 1) >> PAGE_SHIFT;
gfn_t nr_pages_needed = end_gfn - start_gfn + 1;
gfn_t nr_pages_avail;
int r = start_gfn <= end_gfn ? 0 : -EINVAL;
ghc->gpa = gpa;
/* Update ghc->generation before performing any error checks. */
ghc->generation = slots->generation;
ghc->len = len;
if (start_gfn > end_gfn) {
ghc->hva = KVM_HVA_ERR_BAD;
return -EINVAL;
}
/*
* If the requested region crosses two memslots, we still
* verify that the entire region is valid here.
*/
while (!r && start_gfn <= end_gfn) {
for ( ; start_gfn <= end_gfn; start_gfn += nr_pages_avail) {
ghc->memslot = __gfn_to_memslot(slots, start_gfn);
ghc->hva = gfn_to_hva_many(ghc->memslot, start_gfn,
&nr_pages_avail);
if (kvm_is_error_hva(ghc->hva))
r = -EFAULT;
start_gfn += nr_pages_avail;
return -EFAULT;
}
/* Use the slow path for cross page reads and writes. */
if (!r && nr_pages_needed == 1)
if (nr_pages_needed == 1)
ghc->hva += offset;
else
ghc->memslot = NULL;
return r;
ghc->gpa = gpa;
ghc->len = len;
return 0;
}
int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,