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| author | Michal Hocko <mhocko@suse.com> | 2017-07-10 15:49:51 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-07-10 16:32:33 -0700 |
| commit | 561b5e0709e4a248c67d024d4d94b6e31e3edf2f (patch) | |
| tree | 8a5424e03ba4704bb57309eeaeb85fe10a10a598 /mm | |
| parent | bb01b64cfab7c22f3848cb73dc0c2b46b8d38499 (diff) | |
| download | lwn-561b5e0709e4a248c67d024d4d94b6e31e3edf2f.tar.gz lwn-561b5e0709e4a248c67d024d4d94b6e31e3edf2f.zip | |
mm/mmap.c: do not blow on PROT_NONE MAP_FIXED holes in the stack
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.GA18027@dhcp22.suse.cz
Signed-off-by: Michal Hocko <mhocko@suse.com>
Debugged-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/mmap.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/mm/mmap.c b/mm/mmap.c index 7f8cfe9d9b4d..d1902872414f 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2244,7 +2244,8 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address) 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? */ @@ -2328,7 +2329,8 @@ int expand_downwards(struct vm_area_struct *vma, 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? */ |