From 7f8189068726492950bf1a2dcfd9b51314560abf Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 20 Jun 2009 09:52:27 -0700 Subject: [PATCH] x86: don't use 'access_ok()' as a range check in get_user_pages_fast() It's really not right to use 'access_ok()', since that is meant for the normal "get_user()" and "copy_from/to_user()" accesses, which are done through the TLB, rather than through the page tables. Why? access_ok() does both too few, and too many checks. Too many, because it is meant for regular kernel accesses that will not honor the 'user' bit in the page tables, and because it honors the USER_DS vs KERNEL_DS distinction that we shouldn't care about in GUP. And too few, because it doesn't do the 'canonical' check on the address on x86-64, since the TLB will do that for us. So instead of using a function that isn't meant for this, and does something else and much more complicated, just do the real rules: we don't want the range to overflow, and on x86-64, we want it to be a canonical low address (on 32-bit, all addresses are canonical). Acked-by: Ingo Molnar Cc: H. Peter Anvin Cc: Thomas Gleixner Signed-off-by: Linus Torvalds --- arch/x86/mm/gup.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c index 6340cef6798..f9748094126 100644 --- a/arch/x86/mm/gup.c +++ b/arch/x86/mm/gup.c @@ -247,10 +247,15 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write, start &= PAGE_MASK; addr = start; len = (unsigned long) nr_pages << PAGE_SHIFT; + end = start + len; - if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ, - (void __user *)start, len))) + if (end < start) + goto slow_irqon; + +#ifdef CONFIG_X86_64 + if (end >> __VIRTUAL_MASK_SHIFT) goto slow_irqon; +#endif /* * XXX: batch / limit 'nr', to avoid large irq off latency -- 2.32.0.93.g670b81a890