Re: [PATCH] mm/migrate: initialize pud_entry in migrate_vma()

[Ralph Campbell <rcampbell@nvidia.com>]

On 8/26/19 8:11 AM, Vlastimil Babka wrote:
> On 7/20/19 1:32 AM, Ralph Campbell wrote:
>> When CONFIG_MIGRATE_VMA_HELPER is enabled, migrate_vma() calls
>> migrate_vma_collect() which initializes a struct mm_walk but
>> didn't initialize mm_walk.pud_entry. (Found by code inspection)
>> Use a C structure initialization to make sure it is set to NULL.
>>
>> Fixes: 8763cb45ab967 ("mm/migrate: new memory migration helper for use with
>> device memory")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
>> Cc: "Jérôme Glisse" <jglisse@redhat.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
> 
> So this bug can manifest by some garbage address on stack being called, right? I
> wonder, how comes it didn't actually happen yet?

Right.
Probably because HMM isn't widely being used in production yet.

> 
>> ---
>>   mm/migrate.c | 17 +++++++----------
>>   1 file changed, 7 insertions(+), 10 deletions(-)
>>
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 515718392b24..a42858d8e00b 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -2340,16 +2340,13 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
>>   static void migrate_vma_collect(struct migrate_vma *migrate)
>>   {
>>   	struct mmu_notifier_range range;
>> -	struct mm_walk mm_walk;
>> -
>> -	mm_walk.pmd_entry = migrate_vma_collect_pmd;
>> -	mm_walk.pte_entry = NULL;
>> -	mm_walk.pte_hole = migrate_vma_collect_hole;
>> -	mm_walk.hugetlb_entry = NULL;
>> -	mm_walk.test_walk = NULL;
>> -	mm_walk.vma = migrate->vma;
>> -	mm_walk.mm = migrate->vma->vm_mm;
>> -	mm_walk.private = migrate;
>> +	struct mm_walk mm_walk = {
>> +		.pmd_entry = migrate_vma_collect_pmd,
>> +		.pte_hole = migrate_vma_collect_hole,
>> +		.vma = migrate->vma,
>> +		.mm = migrate->vma->vm_mm,
>> +		.private = migrate,
>> +	};
>>   
>>   	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm_walk.mm,
>>   				migrate->start,
>>
>