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Title: s390/mm: four page table levels vs. fork Status in linux package in Ubuntu: New Bug description: == Comment: #0 - Hendrik Brueckner <brueck...@de.ibm.com> - 2016-03-11 08:30:57 == Please backport: http://git.kernel.org/cgit/linux/kernel/git/s390/linux.git/commit/?h =for-linus&id=3446c13b268af86391d06611327006b059b8bab1 s390/mm: four page table levels vs. fork The fork of a process with four page table levels is broken since git commit 6252d702c5311ce9 "[S390] dynamic page tables." All new mm contexts are created with three page table levels and an asce limit of 4TB. If the parent has four levels dup_mmap will add vmas to the new context which are outside of the asce limit. The subsequent call to copy_page_range will walk the three level page table structure of the new process with non-zero pgd and pud indexes. This leads to memory clobbers as the pgd_index *and* the pud_index is added to the mm->pgd pointer without a pgd_deref in between. The init_new_context() function is selecting the number of page table levels for a new context. The function is used by mm_init() which in turn is called by dup_mm() and mm_alloc(). These two are used by fork() and exec(). The init_new_context() function can distinguish the two cases by looking at mm->context.asce_limit, for fork() the mm struct has been copied and the number of page table levels may not change. For exec() the mm_alloc() function set the new mm structure to zero, in this case a three-level page table is created as the temporary stack space is located at STACK_TOP_MAX = 4TB. This fixes CVE-2016-2143. Reported-by: Marcin Ko?cielnicki <koria...@0x04.net> Reviewed-by: Heiko Carstens <heiko.carst...@de.ibm.com> Cc: sta...@vger.kernel.org Signed-off-by: Martin Schwidefsky <schwidef...@de.ibm.com> To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1556141/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
