Re: [Xen-devel] [PATCH] x86/hvm: Fix use-after-free introduced by c/s 428607a

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.02.16 at 11:48, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 02/02/16 10:43, Jan Beulich wrote:
>>>>> On 01.02.16 at 18:56, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> For safety, NULL out the pointers after freeing them, in an attempt to make
>>> mistakes more obvious in the future.
>> Except that NULLing isn't really adding that much safety, and we'd
>> be better off poisoning such pointers. Nevertheless ...
> 
> NULLing the pointers would cause things like rtc_deinit() to always blow
> up when it followed the NULL pointer.
> 
> IMO, we should unconditionally always NULL pointers when freeing a
> pointer which isn't in local scope.  It would make issues such as these
> completely obvious.

As would poisoning the pointers, yet poisoning has the advantage
of not allowing PV guests to control what the hypervisor might
access when erroneously de-referencing such a pointer.

Jan


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