linux-kernel - Re: [PATCH] x86: do not overrun page table ranges in gup

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Message-ID: <alpine.LFD.1.10.0807281737480.3486@nehalem.linux-foundation.org>
Date:	Mon, 28 Jul 2008 17:39:18 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Johannes Weiner <hannes@...urebad.de>
cc:	Alexey Dobriyan <adobriyan@...il.com>, akpm@...uxfoundation.org,
	torvalds@...uxfoundation.org, npiggin@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: do not overrun page table ranges in gup



On Mon, 28 Jul 2008, Linus Torvalds wrote:
> 
> So no, the right fix would be to align 'start' first, which means that 
> everything else (including 'end') will be page-aligned. Aligning just one 
> or the other is very very wrong.

Does this work?

Not pretty, but it stands _some_ chance of being correct.

		Linus


---
 arch/x86/mm/gup.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index 3085f25..007bb06 100644
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -223,14 +223,17 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 			struct page **pages)
 {
 	struct mm_struct *mm = current->mm;
-	unsigned long end = start + (nr_pages << PAGE_SHIFT);
-	unsigned long addr = start;
+	unsigned long addr, len, end;
 	unsigned long next;
 	pgd_t *pgdp;
 	int nr = 0;
 
+	start &= PAGE_MASK;
+	addr = start;
+	len = (unsigned long) nr_pages << PAGE_SHIFT;
+	end = start + len;
 	if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
-					start, nr_pages*PAGE_SIZE)))
+					start, len)))
 		goto slow_irqon;
 
 	/*
--
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