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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2016-10-20 00:49:40 +0200 |
|---|---|---|
| committer | Simon Shields <keepcalm444@gmail.com> | 2016-10-22 13:35:25 +1100 |
| commit | 6c0837fc69be45a1a1bf91c433ac3a4955597c4e (patch) | |
| tree | 323245f250fb5d9955e750eb64d708edff292eec /include | |
| parent | a20c4e114c47ab6c34025110cd44775df36079b0 (diff) | |
| download | kernel_samsung_smdk4412-6c0837fc69be45a1a1bf91c433ac3a4955597c4e.tar.gz kernel_samsung_smdk4412-6c0837fc69be45a1a1bf91c433ac3a4955597c4e.tar.bz2 kernel_samsung_smdk4412-6c0837fc69be45a1a1bf91c433ac3a4955597c4e.zip | |
mm: remove gup_flags FOLL_WRITE games from __get_user_pages()
This is an ancient bug that was actually attempted to be fixed once
(badly) by me eleven years ago in commit 4ceb5db9757a ("Fix
get_user_pages() race for write access") but that was then undone due to
problems on s390 by commit f33ea7f404e5 ("fix get_user_pages bug").
In the meantime, the s390 situation has long been fixed, and we can now
fix it by checking the pte_dirty() bit properly (and do it better). The
s390 dirty bit was implemented in abf09bed3cce ("s390/mm: implement
software dirty bits") which made it into v3.9. Earlier kernels will
have to look at the page state itself.
Also, the VM has become more scalable, and what used a purely
theoretical race back then has become easier to trigger.
To fix it, we introduce a new internal FOLL_COW flag to mark the "yes,
we already did a COW" rather than play racy games with FOLL_WRITE that
is very fundamental, and then use the pte dirty flag to validate that
the FOLL_COW flag is still valid.
Change-Id: Id9bec3722797dff7d0ff0d9f6097c4229e31fd62
Reported-and-tested-by: Phil "not Paul" Oester <kernel@linuxace.com>
Acked-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Michal Hocko <mhocko@suse.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Nick Piggin <npiggin@gmail.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[wt: s/gup.c/memory.c; s/follow_page_pte/follow_page_mask;
s/faultin_page/__get_user_page]
Signed-off-by: Willy Tarreau <w@1wt.eu>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/mm.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index 92a055bd3dd..b465c7f716c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1574,6 +1574,7 @@ struct page *follow_page(struct vm_area_struct *, unsigned long address, #define FOLL_SPLIT 0x80 /* don't return transhuge pages, split them */ #define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */ #define FOLL_NO_CMA 0x200 /* avoid putting pages to CMA regions */ +#define FOLL_COW 0x4000 /* internal GUP flag */ typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr, void *data); |