On 07/02/2018 12:15 PM, Greg KH wrote:
> On Mon, Jul 02, 2018 at 11:48:28AM +0300, Andrey Ryabinin wrote:
>> commit 0e311d237d7f3022b7dafb639b42541bfb42fe94 upstream.
>>
>> When the P4D page table layer is folded at runtime, the p4d_free()
>> should do nothing, the same as in <asm-generic/pgtable-nop4d.h>.
>>
>> It seems this bug should cause double-free in efi_call_phys_epilog(),
>> but I don't know how to trigger that code path, so I can't confirm that
>> by testing.
>>
>> Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
>> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
>> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> Cc: stable@xxxxxxxxxxxxxxx # 4.17
>> Fixes: 98219dda2ab5 ("x86/mm: Fold p4d page table layer at runtime")
>> Link: http://lkml.kernel.org/r/20180625102427.15015-1-aryabinin@xxxxxxxxxxxxx
>> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
>> Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
>> ---
>>
>> Changes since v1:
>> - Fix wrong "From:" field
>>
>> arch/x86/include/asm/pgalloc.h | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/pgalloc.h b/arch/x86/include/asm/pgalloc.h
>> index 263c142a6a6c..f65e9e1cea4c 100644
>> --- a/arch/x86/include/asm/pgalloc.h
>> +++ b/arch/x86/include/asm/pgalloc.h
>> @@ -184,6 +184,9 @@ static inline p4d_t *p4d_alloc_one(struct mm_struct *mm, unsigned long addr)
>>
>> static inline void p4d_free(struct mm_struct *mm, p4d_t *p4d)
>> {
>> + if (!pgtable_l5_enabled)
>> + return;
>> +
>
> Again, did you actually test-build this?
Again, yes, I did test-build this.
> What changed from the original
> patch which blew the build up into little tiny pieces?
>
Removed '()'. In 4.17 pgtable_l5_enabled is variable, in 4.18 it's function.
> greg k-h
>
