On 2/21/22 23:47, Michal Hocko wrote:
> On Mon 21-02-22 12:24:25, Mike Kravetz wrote:
>> On 2/21/22 00:42, Michal Hocko wrote:
>>> On Fri 18-02-22 13:29:46, Mike Kravetz wrote:
>>> [...]
>>>> @@ -4161,7 +4162,7 @@ static int __init hugepages_setup(char *s)
>>>> }
>>>> if (tmp >= nr_online_nodes)
>>>> goto invalid;
>>>> - node = tmp;
>>>> + node = array_index_nospec(tmp, nr_online_nodes);
>>>> p += count + 1;
>>>> /* Parse hugepages */
>>>> if (sscanf(p, "%lu%n", &tmp, &count) != 1)
>>>> @@ -6889,9 +6890,9 @@ static int __init cmdline_parse_hugetlb_cma(char *p)
>>>> break;
>>>>
>>>> if (s[count] == ':') {
>>>> - nid = tmp;
>>>> - if (nid < 0 || nid >= MAX_NUMNODES)
>>>> + if (tmp >= MAX_NUMNODES)
>>>> break;
>>>> + nid = array_index_nospec(tmp, MAX_NUMNODES);
>>>>
>>>> s += count + 1;
>>>> tmp = memparse(s, &s);
>>>
>>> This is an early boot code, how is this supposed to be used as a side
>>> channel?
>>
>> I do not have an evil hacker mind, but I can not think of a way this one time
>> use of a user specified index could be an issue. It does add noise to the
>> BUILD REGRESSION emails sent to Andrew.
>
> Maybe Smack can be taught to ignore __init and other early boot
> functions.
>
> I do not have any strong objections to using array_index_nospec because
> it won't do any harm. Except that it makes a security measure a normal
> comodity so any future changes to array_index_nospec and its users will
> have to consult additional callers. Whether that is something we should
> deeply care about, I don't know.
>
> At minimum make sure to be explicit that this can hardly be a Spectre
> gadget as it is a _one_ time early boot call. If there is a scenario
> where this could be really abused then it should be mentioned
> explicitly.
How about adding this note to the commit message?
Note: these routines take a user specified value used as an index ONCE
during the boot process. As a result, they can not be used as a general
method of exploitation. Code changes are being made to eliminate warnings.
Andrew, would you like me to send a v3?
--
Mike Kravetz
