Re: [4.19.y PATCH 1/3] efi/x86/Add missing error handling to old_memmap 1:1 mapping code

Srivatsa S. Bhat
2019-06-29T21:49:44Z

On 6/29/19 2:11 PM, Ard Biesheuvel wrote:
> On Sat, 29 Jun 2019 at 11:11, Greg KH <gregkh@linuxfoundation.org> wrote:
>>
>> On Sat, Jun 29, 2019 at 10:47:00AM +0200, Ard Biesheuvel wrote:
>>> On Sat, 29 Jun 2019 at 08:57, Greg KH <gregkh@linuxfoundation.org> wrote:
>>>>
>>>> On Fri, Jun 28, 2019 at 11:42:13AM -0700, Srivatsa S. Bhat wrote:
>>>>> From: Gen Zhang <blackgod016574@gmail.com>
>>>>>
>>>>> commit 4e78921ba4dd0aca1cc89168f45039add4183f8e upstream.
>>>>>
>>>>> The old_memmap flow in efi_call_phys_prolog() performs numerous memory
>>>>> allocations, and either does not check for failure at all, or it does
>>>>> but fails to propagate it back to the caller, which may end up calling
>>>>> into the firmware with an incomplete 1:1 mapping.
>>>>>
>>>>> So let's fix this by returning NULL from efi_call_phys_prolog() on
>>>>> memory allocation failures only, and by handling this condition in the
>>>>> caller. Also, clean up any half baked sets of page tables that we may
>>>>> have created before returning with a NULL return value.
>>>>>
>>>>> Note that any failure at this level will trigger a panic() two levels
>>>>> up, so none of this makes a huge difference, but it is a nice cleanup
>>>>> nonetheless.
>>>>
>>>> With a description like this, why is this needed in a stable kernel if
>>>> it does not really fix anything useful?
>>>>
>>>
>>> Because it fixes a 'CVE', remember? :-)
>>
>> No, I don't remember that at all.
>>
>> Remember, I get 1000+ emails a day to do something with, and hence, have
>> the short-term memory of prior emails of a squirrel.
>>
>> Also, CVEs mean nothing, anyone can get one and they are impossible to
>> revoke, so don't treat them like they are "authoritative" at all.
>>
>
> To refresh your memory: I already nacked this backport once before, on
> the grounds that the CVE is completely bogus.
>

Oh! I didn't know that this patch was discussed here before (this is
the first time I'm posting these backports). Anyway, based on the
discussion above, Greg, please ignore this patchset.

Regards,
Srivatsa