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-   -   SRU: Fix (hopefully) the last stack guard page effect (http://www.linux-archive.org/ubuntu-kernel-team/427819-sru-fix-hopefully-last-stack-guard-page-effect.html)

Brad Figg 09-16-2010 01:14 PM

SRU: Fix (hopefully) the last stack guard page effect
 
On 09/14/2010 09:04 AM, Stefan Bader wrote:
> SRU Justification:
>
> Impact: When introducing the stack guard page, a follow up patch tried to
> minimize the effects user-space sees from this change. Unfortunately a
> lot of the checks did not take into account that user-space may mlock a
> portion of the stack, but not all of it. This causes the stack vma to
> be split and a lot of assumptions to go down the drain. Most places have
> been fixed by now but looking at /proc/<pid>/maps when a stack vma has
> been split still hides a page on every area and not only on head of it
> as it was intended.
>
> Fix: The following upstream change makes one inline available to other
> code and uses that when checking for the guard page in the proc output.
>
> Testcase: A program that mlocks an area of the stack and then dumps its
> maps will see holes before the patch and none after.
>
> Note: When providing incremental patches to Linus, the cc for stable got
> lost, though I pinged Greg, but have not received an answer yet. In the
> end it hopefully comes from stable. I have not yet created a bug report
> for it as I am not really sure how urgent this is to fix.
>
> -Stefan
>
> ---
>
> From 39aa3cb3e8250db9188a6f1e3fb62ffa1a717678 Mon Sep 17 00:00:00 2001
> From: Stefan Bader<stefan.bader@canonical.com>
> Date: Tue, 31 Aug 2010 15:52:27 +0200
> Subject: [PATCH] mm: (pre-stable) Move vma_stack_continue into mm.h
>
> So it can be used by all that need to check for that.
>
> Signed-off-by: Stefan Bader<stefan.bader@canonical.com>
> Signed-off-by: Linus Torvalds<torvalds@linux-foundation.org>
> (cherry-picked from commit 39aa3cb3e8250db9188a6f1e3fb62ffa1a717678 upstream)
> Signed-off-by: Stefan Bader<stefan.bader@canonical.com>
> ---
> fs/proc/task_mmu.c | 3 ++-
> include/linux/mm.h | 6 ++++++
> mm/mlock.c | 6 ------
> 3 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 439fc1f..271afc4 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -224,7 +224,8 @@ static void show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
> /* We don't show the stack guard page in /proc/maps */
> start = vma->vm_start;
> if (vma->vm_flags& VM_GROWSDOWN)
> - start += PAGE_SIZE;
> + if (!vma_stack_continue(vma->vm_prev, vma->vm_start))
> + start += PAGE_SIZE;
>
> seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
> start,
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e6b1210..74949fb 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -864,6 +864,12 @@ int set_page_dirty(struct page *page);
> int set_page_dirty_lock(struct page *page);
> int clear_page_dirty_for_io(struct page *page);
>
> +/* Is the vma a continuation of the stack vma above it? */
> +static inline int vma_stack_continue(struct vm_area_struct *vma, unsigned long addr)
> +{
> + return vma&& (vma->vm_end == addr)&& (vma->vm_flags& VM_GROWSDOWN);
> +}
> +
> extern unsigned long move_page_tables(struct vm_area_struct *vma,
> unsigned long old_addr, struct vm_area_struct *new_vma,
> unsigned long new_addr, unsigned long len);
> diff --git a/mm/mlock.c b/mm/mlock.c
> index cbae7c5..b70919c 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -135,12 +135,6 @@ void munlock_vma_page(struct page *page)
> }
> }
>
> -/* Is the vma a continuation of the stack vma above it? */
> -static inline int vma_stack_continue(struct vm_area_struct *vma, unsigned long addr)
> -{
> - return vma&& (vma->vm_end == addr)&& (vma->vm_flags& VM_GROWSDOWN);
> -}
> -
> static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long addr)
> {
> return (vma->vm_flags& VM_GROWSDOWN)&&


Acked-by: Brad Figg <brad.figg@canonical.com>

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Brad Figg brad.figg@canonical.com http://www.canonical.com

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