Re: [PATCH 2/3] KVM: Check validity of offset+length of gfn_to_pfn_cache prior to activation

[Paul Durrant]

On 20/03/2024 00:15, Sean Christopherson wrote:
> When activating a gfn_to_pfn_cache, verify that the offset+length is sane
> and usable before marking the cache active.  Letting __kvm_gpc_refresh()
> detect the problem results in a cache being marked active without setting
> the GPA (or any other fields), which in turn results in KVM trying to
> refresh a cache with INVALID_GPA.
>
> Attempting to refresh a cache with INVALID_GPA isn't functionally
> problematic, but it runs afoul of the sanity check that exactly one of
> GPA or userspace HVA is valid, i.e. that a cache is either GPA-based or
> HVA-based.
>
> Reported-by: syzbot+106a4f72b0474e1d1b33@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://lore.kernel.org/all/0000000000005fa5cc0613f1cebd@xxxxxxxxxx
> Fixes: 721f5b0dda78 ("KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA")
> Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
> Cc: Paul Durrant <paul@xxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>   virt/kvm/pfncache.c | 16 +++++++++-------
>   1 file changed, 9 insertions(+), 7 deletions(-)

Reviewed-by: Paul Durrant <paul@xxxxxxx>