On Fri, Jun 17, 2016 at 1:30 PM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> On Fri, Jun 17, 2016 at 01:00:39PM -0700, Andy Lutomirski wrote:
>> It's currently only used in the EFI code, which is safe AFAICT.
>
> "It is basically useful for a pagetable hierarchy which is not init_mm."
>
>> Warn if anyone tries to use it on the normal kernel pgd.
>>
>> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
>> ---
>> arch/x86/mm/pageattr.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
>> index 6a8026918bf6..e9b9c5cedbb8 100644
>> --- a/arch/x86/mm/pageattr.c
>> +++ b/arch/x86/mm/pageattr.c
>> @@ -1996,6 +1996,9 @@ out:
>> void kernel_unmap_pages_in_pgd(pgd_t *root, unsigned long address,
>> unsigned numpages)
>> {
>> + /* Unmapping kernel entries from init_mm's pgd is not allowed. */
>> + WARN_ON(root == init_mm.pgd);
>
> We can also return and not do the unmapping:
>
> if (WARN_ON(root == init_mm.pgd))
> return;
I'll do one better: the only function that calls this function is
unused. I'll just delete it.
--Andy
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