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authorLinus Torvalds <torvalds@linux-foundation.org>2010-08-15 11:35:52 -0700
committerGreg Kroah-Hartman <gregkh@suse.de>2010-08-20 11:34:24 -0700
commite4599a4a45259b9cfb0942d36f6f35f3dca1d893 (patch)
treef49aa4b2cb9d15b7273f26e7c135729e5f96795d
parent058daedc8311ab42702dfe29d3ff16dff7e7eaf8 (diff)
mm: fix up some user-visible effects of the stack guard page
commit d7824370e26325c881b665350ce64fb0a4fde24a upstream. This commit makes the stack guard page somewhat less visible to user space. It does this by: - not showing the guard page in /proc/<pid>/maps It looks like lvm-tools will actually read /proc/self/maps to figure out where all its mappings are, and effectively do a specialized "mlockall()" in user space. By not showing the guard page as part of the mapping (by just adding PAGE_SIZE to the start for grows-up pages), lvm-tools ends up not being aware of it. - by also teaching the _real_ mlock() functionality not to try to lock the guard page. That would just expand the mapping down to create a new guard page, so there really is no point in trying to lock it in place. It would perhaps be nice to show the guard page specially in /proc/<pid>/maps (or at least mark grow-down segments some way), but let's not open ourselves up to more breakage by user space from programs that depends on the exact deails of the 'maps' file. Special thanks to Henrique de Moraes Holschuh for diving into lvm-tools source code to see what was going on with the whole new warning. Reported-and-tested-by: Fran├žois Valenduc <francois.valenduc@tvcablenet.be Reported-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--fs/proc/task_mmu.c8
-rw-r--r--mm/mlock.c8
2 files changed, 15 insertions, 1 deletions
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 366b1017a4f1..899145d48207 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -206,6 +206,7 @@ static void show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
int flags = vma->vm_flags;
unsigned long ino = 0;
unsigned long long pgoff = 0;
+ unsigned long start;
dev_t dev = 0;
int len;
@@ -216,8 +217,13 @@ static void show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
pgoff = ((loff_t)vma->vm_pgoff) << PAGE_SHIFT;
}
+ /* We don't show the stack guard page in /proc/maps */
+ start = vma->vm_start;
+ if (vma->vm_flags & VM_GROWSDOWN)
+ start += PAGE_SIZE;
+
seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
- vma->vm_start,
+ start,
vma->vm_end,
flags & VM_READ ? 'r' : '-',
flags & VM_WRITE ? 'w' : '-',
diff --git a/mm/mlock.c b/mm/mlock.c
index 2e05c97b04f5..524d2a444ef7 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -170,6 +170,14 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
if (vma->vm_flags & VM_WRITE)
gup_flags |= FOLL_WRITE;
+ /* We don't try to access the guard page of a stack vma */
+ if (vma->vm_flags & VM_GROWSDOWN) {
+ if (start == vma->vm_start) {
+ start += PAGE_SIZE;
+ nr_pages--;
+ }
+ }
+
while (nr_pages > 0) {
int i;