On Thu, Dec 13, 2018 at 01:10:21PM -0800, Jim Mattson wrote:
> Avoid potential out-of-bounds writes due to negative offsets. Note
> that all current call sites are fine.
Oof. It'd be helpful if the changelog went into a bit more detail on
how an out-of-bounds write is possible, e.g. even just a small blurb
that says offset is used to directly adjust the gpa/hva. It wasn't
immediately obvious (to me) that a negative offset was bad because the
existing bounds check makes it look ok at first glance...
BUG_ON(len + offset > ghc->len);
Tangentially related, seems like this should be:
if (WARN_ON(...))
return -EFAULT;
Reviewed-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> Fixes: 4ec6e8636256 ("kvm: Introduce kvm_write_guest_offset_cached()")
> Reported-by: Cfir Cohen <cfir@xxxxxxxxxx>
> Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
> Reviewed-by: Cfir Cohen <cfir@xxxxxxxxxx>
> Reviewed-by: Peter Shier <pshier@xxxxxxxxxx>
> ---
> include/linux/kvm_host.h | 3 ++-
> virt/kvm/kvm_main.c | 3 ++-
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index c926698040e0d..a03d5e264e5e7 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -694,7 +694,8 @@ int kvm_write_guest(struct kvm *kvm, gpa_t gpa, const void *data,
> int kvm_write_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
> void *data, unsigned long len);
> int kvm_write_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
> - void *data, int offset, unsigned long len);
> + void *data, unsigned int offset,
> + unsigned long len);
> int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
> gpa_t gpa, unsigned long len);
> int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 2679e476b6c39..065ee2fb40340 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1965,7 +1965,8 @@ int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
> EXPORT_SYMBOL_GPL(kvm_gfn_to_hva_cache_init);
>
> int kvm_write_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
> - void *data, int offset, unsigned long len)
> + void *data, unsigned int offset,
> + unsigned long len)
> {
> struct kvm_memslots *slots = kvm_memslots(kvm);
> int r;
> --
> 2.20.0.rc2.403.gdbc3b29805-goog
>
