new in v5: - patches 1-3 and 6 are unchanged - added patch 4: rework vma_dump_size() into a common helper (Linus) - added patch 7: actually do the mmget_still_valid() removal (Linus) - for now, let dump_vma_snapshot() take the mmap_lock in write mode instead of read mode to avoid the data race with stack expansion new in v4: - simplify patch 4/5 by replacing the heuristic for dumping the first pages of ELF mappings with what Linus suggested At the moment, we have that rather ugly mmget_still_valid() helper to work around <https://crbug.com/project-zero/1790>: ELF core dumping doesn't take the mmap_sem while traversing the task's VMAs, and if anything (like userfaultfd) then remotely messes with the VMA tree, fireworks ensue. So at the moment we use mmget_still_valid() to bail out in any writers that might be operating on a remote mm's VMAs. With this series, I'm trying to get rid of the need for that as cleanly as possible. ("cleanly" meaning "avoid holding the mmap_lock across unbounded sleeps".) Patches 1, 2, 3 and 4 are relatively unrelated cleanups in the core dumping code. Patches 5 and 6 implement the main change: Instead of repeatedly accessing the VMA list with sleeps in between, we snapshot it at the start with proper locking, and then later we just use our copy of the VMA list. This ensures that the kernel won't crash, that VMA metadata in the coredump is consistent even in the presence of concurrent modifications, and that any virtual addresses that aren't being concurrently modified have their contents show up in the core dump properly. The disadvantage of this approach is that we need a bit more memory during core dumping for storing metadata about all VMAs. At the end of the series, patch 7 removes the old workaround for this issue (mmget_still_valid()). I have tested: - Creating a simple core dump on X86-64 still works. - The created coredump on X86-64 opens in GDB and looks plausible. - X86-64 core dumps contain the first page for executable mappings at offset 0, and don't contain the first page for non-executable file mappings or executable mappings at offset !=0. - NOMMU 32-bit ARM can still generate plausible-looking core dumps through the FDPIC implementation. (I can't test this with GDB because GDB is missing some structure definition for nommu ARM, but I've poked around in the hexdump and it looked decent.) Jann Horn (7): binfmt_elf_fdpic: Stop using dump_emit() on user pointers on !MMU coredump: Let dump_emit() bail out on short writes coredump: Refactor page range dumping into common helper coredump: Rework elf/elf_fdpic vma_dump_size() into common helper binfmt_elf, binfmt_elf_fdpic: Use a VMA list snapshot mm/gup: Take mmap_lock in get_dump_page() mm: Remove the now-unnecessary mmget_still_valid() hack drivers/infiniband/core/uverbs_main.c | 3 - drivers/vfio/pci/vfio_pci.c | 38 ++-- fs/binfmt_elf.c | 238 +++----------------------- fs/binfmt_elf_fdpic.c | 162 +++--------------- fs/coredump.c | 236 +++++++++++++++++++++++-- fs/proc/task_mmu.c | 18 -- fs/userfaultfd.c | 28 +-- include/linux/coredump.h | 11 ++ include/linux/sched/mm.h | 25 --- mm/gup.c | 61 +++---- mm/khugepaged.c | 2 +- mm/madvise.c | 17 -- mm/mmap.c | 5 +- 13 files changed, 346 insertions(+), 498 deletions(-) base-commit: 06a4ec1d9dc652e17ee3ac2ceb6c7cf6c2b75cdd -- 2.28.0.297.g1956fa8f8d-goog
