Re: [PATCH v4 1/2] kvm: vmx: fix limit checking in get_vmx_mem_address()

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Thu, Jun 06, 2019 at 12:17:39AM +0300, Eugene Korenevsky wrote:
> Intel SDM vol. 3, 5.3:
> The processor causes a
> general-protection exception (or, if the segment is SS, a stack-fault
> exception) any time an attempt is made to access the following addresses
> in a segment:
> - A byte at an offset greater than the effective limit
> - A word at an offset greater than the (effective-limit – 1)
> - A doubleword at an offset greater than the (effective-limit – 3)
> - A quadword at an offset greater than the (effective-limit – 7)
> 
> Therefore, the generic limit checking error condition must be
> 
> exn = (off > limit + 1 - access_len) = (off + access_len - 1 > limit)
> 
> but not
> 
> exn = (off + access_len > limit)
> 
> as for now.
> 
> Also avoid integer overflow of `off` at 32-bit KVM by casting it to u64.
> 
> Note: access length is currently sizeof(u64) which is incorrect. This
> will be fixed in the subsequent patch.
> 
> Signed-off-by: Eugene Korenevsky <ekorenevsky@gmail.com>
> ---

Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>