Hi David,
Thank you for quick review!
On 2/13/23 4:44 PM, David Hildenbrand wrote:
> On 13.02.23 11:43, Muhammad Usama Anjum wrote:
>> mwriteprotect_range() errors out if [start, end) doesn't fall in one
>> VMA. We are facing a use case where multiple VMAs are present in one
>> range of interest. For example, the following pseudocode reproduces the
>> error which we are trying to fix:
>>
>> - Allocate memory of size 16 pages with PROT_NONE with mmap
>> - Register userfaultfd
>> - Change protection of the first half (1 to 8 pages) of memory to
>> PROT_READ | PROT_WRITE. This breaks the memory area in two VMAs.
>> - Now UFFDIO_WRITEPROTECT_MODE_WP on the whole memory of 16 pages errors
>> out.
>>
>> This is a simple use case where user may or may not know if the memory
>> area has been divided into multiple VMAs.
>>
>> Reported-by: Paul Gofman <pgofman@xxxxxxxxxxxxxxx>
>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
>> ---
>> mm/userfaultfd.c | 36 +++++++++++++++++++-----------------
>> 1 file changed, 19 insertions(+), 17 deletions(-)
>>
>> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
>> index 65ad172add27..46e0a014af68 100644
>> --- a/mm/userfaultfd.c
>> +++ b/mm/userfaultfd.c
>> @@ -738,9 +738,11 @@ int mwriteprotect_range(struct mm_struct *dst_mm,
>> unsigned long start,
>> unsigned long len, bool enable_wp,
>> atomic_t *mmap_changing)
>> {
>> + unsigned long end = start + len;
>> struct vm_area_struct *dst_vma;
>> unsigned long page_mask;
>> int err;
>> + VMA_ITERATOR(vmi, dst_mm, start);
>> /*
>> * Sanitize the command parameters:
>> @@ -762,26 +764,26 @@ int mwriteprotect_range(struct mm_struct *dst_mm,
>> unsigned long start,
>> if (mmap_changing && atomic_read(mmap_changing))
>> goto out_unlock;
>> - err = -ENOENT;
>> - dst_vma = find_dst_vma(dst_mm, start, len);
>> -
>> - if (!dst_vma)
>> - goto out_unlock;
>> - if (!userfaultfd_wp(dst_vma))
>> - goto out_unlock;
>> - if (!vma_can_userfault(dst_vma, dst_vma->vm_flags))
>> - goto out_unlock;
>> + for_each_vma_range(vmi, dst_vma, end) {
>> + err = -ENOENT;
>> - if (is_vm_hugetlb_page(dst_vma)) {
>> - err = -EINVAL;
>> - page_mask = vma_kernel_pagesize(dst_vma) - 1;
>> - if ((start & page_mask) || (len & page_mask))
>> - goto out_unlock;
>> - }
>> + if (!dst_vma->vm_userfaultfd_ctx.ctx)
>> + break;
>> + if (!userfaultfd_wp(dst_vma))
>> + break;
>> + if (!vma_can_userfault(dst_vma, dst_vma->vm_flags))
>> + break;
>> - uffd_wp_range(dst_mm, dst_vma, start, len, enable_wp);
>> + if (is_vm_hugetlb_page(dst_vma)) {
>> + err = -EINVAL;
>> + page_mask = vma_kernel_pagesize(dst_vma) - 1;
>> + if ((start & page_mask) || (len & page_mask))
>> + break;
>> + }
>> - err = 0;
>> + uffd_wp_range(dst_mm, dst_vma, start, len, enable_wp);
>
> I suspect you should be adjusting the range to only cover that specific VMA
> here.
Sorry, you are right. I don't know why it is still working with the
blunder. Will send a v2.
Thanks,
Usama
--
BR,
Muhammad Usama Anjum
