On Tue, 16 Apr 2019 11:09:06 +0200 Martin Schwidefsky <schwidefsky@xxxxxxxxxx> wrote: > On Mon, 15 Apr 2019 09:17:10 -0700 > Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > On Sun, Apr 14, 2019 at 10:19 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > > > > Can we please have the page refcount overflow fixes out on the list > > > for review, even if it is after the fact? > > > > They were actually on a list for review long before the fact, but it > > was the security mailing list. The issue actually got discussed back > > in January along with early versions of the patches, but then we > > dropped the ball because it just wasn't on anybody's radar and it got > > resurrected late March. Willy wrote a rather bigger patch-series, and > > review of that is what then resulted in those commits. So they may > > look recent, but that's just because the original patches got > > seriously edited down and rewritten. > > First time I hear about this, thanks for the heads up. > > > That said, powerpc and s390 should at least look at maybe adding a > > check for the page ref in their gup paths too. Powerpc has the special > > gup_hugepte() case, and s390 has its own version of gup entirely. I > > was actually hoping the s390 guys would look at using the generic gup > > code. > > We did look at converting the s390 gup code to CONFIG_HAVE_GENERIC_GUP, > there are some details that need careful consideration. The top one > is access_ok(), for s390 we always return true. The generic gup code > relies on the fact that a page table walk with a specific address is > doable if access_ok() returned true, the s390 specific check is slightly > different: > > if ((end <= start) || (end > mm->context.asce_limit)) > return 0; > > The obvious approach would be to modify access_ok() to check against > the asce_limit. I will try and see if anything breaks, e.g. the automatic > page table upgrade. I tested the waters in regard to access_ok() and the generic gup code. The good news is that mm/gup.c with CONFIG_HAVE_GENERIC_GUP=y seems to work just fine if the access_ok() issue is taken care of. But.. Bloat-o-meter with a non-empty uaccess_ok() that checks against current->mm->context.asce_limit: add/remove: 8/2 grow/shrink: 611/11 up/down: 61352/-1914 (59438) with CONFIG_HAVE_GENERIC_GUP on top of that add/remove: 10/2 grow/shrink: 612/12 up/down: 63568/-3280 (60288) This is not nice, would a patch like the following be acceptable? -- Subject: [PATCH] mm: introduce mm_pgd_walk_ok Add the architecture overrideable function mm_pgd_walk_ok() to check if a block of memory is inside the limits of the page table hierarchy of a given mm struct. Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx> --- include/asm-generic/pgtable.h | 4 ++++ mm/gup.c | 4 ++-- 2 files changed, 6 insertions(+), 2 deletions(-) diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h index fa782fba51ee..7d2a8a58f1c1 100644 --- a/include/asm-generic/pgtable.h +++ b/include/asm-generic/pgtable.h @@ -1186,4 +1186,8 @@ static inline bool arch_has_pfn_modify_check(void) #define mm_pmd_folded(mm) __is_defined(__PAGETABLE_PMD_FOLDED) #endif +#ifndef mm_pgd_walk_ok +#define mm_pgd_walk_ok(mm, addr, size) access_ok(addr, size) +#endif + #endif /* _ASM_GENERIC_PGTABLE_H */ diff --git a/mm/gup.c b/mm/gup.c index 91819b8ad9cc..b3eb3f45d237 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1990,7 +1990,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write, len = (unsigned long) nr_pages << PAGE_SHIFT; end = start + len; - if (unlikely(!access_ok((void __user *)start, len))) + if (unlikely(!mm_pgd_walk_ok(current->mm, (void __user *)start, len))) return 0; /* @@ -2044,7 +2044,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write, if (nr_pages <= 0) return 0; - if (unlikely(!access_ok((void __user *)start, len))) + if (unlikely(!mm_pgd_walk_ok(current->mm, (void __user *)start, len))) return -EFAULT; if (gup_fast_permitted(start, nr_pages)) { -- 2.16.4 With an empty access_ok() but a "real" mm_pgd_walk_ok() the results are much more reasonable: add/remove: 2/0 grow/shrink: 2/1 up/down: 2186/-1382 (804) -- blue skies, Martin. "Reality continues to ruin my life." - Calvin.