3.16.49-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Michal Hocko <mho...@suse.com>
commit 561b5e0709e4a248c67d024d4d94b6e31e3edf2f upstream.
Commit 1be7107fbe18 ("mm: larger stack guard gap, between vmas") has
introduced a regression in some rust and Java environments which are
trying to implement their own stack guard page. They are punching a new
MAP_FIXED mapping inside the existing stack Vma.
This will confuse expand_{downwards,upwards} into thinking that the
stack expansion would in fact get us too close to an existing non-stack
vma which is a correct behavior wrt safety. It is a real regression on
the other hand.
Let's work around the problem by considering PROT_NONE mapping as a part
of the stack. This is a gros hack but overflowing to such a mapping
would trap anyway an we only can hope that usespace knows what it is
doing and handle it propely.
Fixes: 1be7107fbe18 ("mm: larger stack guard gap, between vmas")
Link: http://lkml.kernel.org/r/20170705182849.ga18...@dhcp22.suse.cz
Signed-off-by: Michal Hocko <mho...@suse.com>
Debugged-by: Vlastimil Babka <vba...@suse.cz>
Cc: Ben Hutchings <b...@decadent.org.uk>
Cc: Willy Tarreau <w...@1wt.eu>
Cc: Oleg Nesterov <o...@redhat.com>
Cc: Rik van Riel <r...@redhat.com>
Cc: Hugh Dickins <hu...@google.com>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
mm/mmap.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2153,7 +2153,8 @@ int expand_upwards(struct vm_area_struct
gap_addr = TASK_SIZE;
next = vma->vm_next;
- if (next && next->vm_start < gap_addr) {
+ if (next && next->vm_start < gap_addr &&
+ (next->vm_flags & (VM_WRITE|VM_READ|VM_EXEC))) {
if (!(next->vm_flags & VM_GROWSUP))
return -ENOMEM;
/* Check that both stack segments have the same anon_vma? */
@@ -2233,7 +2234,8 @@ int expand_downwards(struct vm_area_stru
if (gap_addr > address)
return -ENOMEM;
prev = vma->vm_prev;
- if (prev && prev->vm_end > gap_addr) {
+ if (prev && prev->vm_end > gap_addr &&
+ (prev->vm_flags & (VM_WRITE|VM_READ|VM_EXEC))) {
if (!(prev->vm_flags & VM_GROWSDOWN))
return -ENOMEM;
/* Check that both stack segments have the same anon_vma? */
