On 07/25/22 17:07, Miaohe Lin wrote: > Hi all: > When I investigate the mm/hugetlb code, I found there's a possible data leak issue > with huge pmd sharing. Thank about the below scene: > > 1. Process A and process B shares huge pmd page.(vm_flags: VM_MAYSHARE but !VM_SHARED) Thanks, I often get confused about the setting of VM_MAYSHARE and VM_SHARED. When you throw in the possibility of shared and anonymous, then I struggle a bit more. At one time did an audit to get the meaning clear in my mind, but still struggle with the meanings. Is it possible to have VM_MAYSHARE and !VM_SHARED on a hugetlb vma? I only took a quick look and could not find a way for this to happen. But, I could have easily missed something. -- Mike Kravetz > 2. Process A write fault a hugetlb page. As vm_flags is !VM_SHARED, a private copy of > hugetlb page will be installed in the pagetable via hugetlb_wp. > 3. Process A writes private data into hugetlb page. > 4. Process B can read process A's private data since hugetlb page is shared through huge > pmd sharing... > > I think the above scene is possible. If so, huge pmd sharing for !VM_SHARED should be disabled > to fix this issue? Or am I miss something about hugetlb huge pmd sharing? > > Any response would be appreciated. > > Thanks! :)
