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authorLinus Torvalds <torvalds@linux-foundation.org>2010-08-12 17:54:33 -0700
committerGreg Kroah-Hartman <gregkh@suse.de>2010-08-13 13:20:27 -0700
commit7e281afe24330aeea86113ac241eabdac8ba2311 (patch)
tree23031c0f8276f049a607f33b5da93b006e362559
parent46dc12d5f11adc21f0071f41d251f3e68869213d (diff)
mm: keep a guard page below a grow-down stack segment
commit 320b2b8de12698082609ebbc1a17165727f4c893 upstream. This is a rather minimally invasive patch to solve the problem of the user stack growing into a memory mapped area below it. Whenever we fill the first page of the stack segment, expand the segment down by one page. Now, admittedly some odd application might _want_ the stack to grow down into the preceding memory mapping, and so we may at some point need to make this a process tunable (some people might also want to have more than a single page of guarding), but let's try the minimal approach first. Tested with trivial application that maps a single page just below the stack, and then starts recursing. Without this, we will get a SIGSEGV _after_ the stack has smashed the mapping. With this patch, we'll get a nice SIGBUS just as the stack touches the page just above the mapping. Requested-by: Keith Packard <keithp@keithp.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--mm/memory.c23
1 files changed, 23 insertions, 0 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 348e2066a4f3..92ef198a7670 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2630,6 +2630,26 @@ out_release:
}
/*
+ * This is like a special single-page "expand_downwards()",
+ * except we must first make sure that 'address-PAGE_SIZE'
+ * doesn't hit another vma.
+ *
+ * The "find_vma()" will do the right thing even if we wrap
+ */
+static inline int check_stack_guard_page(struct vm_area_struct *vma, unsigned long address)
+{
+ address &= PAGE_MASK;
+ if ((vma->vm_flags & VM_GROWSDOWN) && address == vma->vm_start) {
+ address -= PAGE_SIZE;
+ if (find_vma(vma->vm_mm, address) != vma)
+ return -ENOMEM;
+
+ expand_stack(vma, address);
+ }
+ return 0;
+}
+
+/*
* We enter with non-exclusive mmap_sem (to exclude vma changes,
* but allow concurrent faults), and pte mapped but not yet locked.
* We return with mmap_sem still held, but pte unmapped and unlocked.
@@ -2642,6 +2662,9 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
spinlock_t *ptl;
pte_t entry;
+ if (check_stack_guard_page(vma, address) < 0)
+ return VM_FAULT_SIGBUS;
+
if (!(flags & FAULT_FLAG_WRITE)) {
entry = pte_mkspecial(pfn_pte(my_zero_pfn(address),
vma->vm_page_prot));