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-rw-r--r--CVE-2017-1000364.mm-larger-stack-guard-gap-between-vmas.patch883
1 files changed, 883 insertions, 0 deletions
diff --git a/CVE-2017-1000364.mm-larger-stack-guard-gap-between-vmas.patch b/CVE-2017-1000364.mm-larger-stack-guard-gap-between-vmas.patch
new file mode 100644
index 00000000000..681fec47a4a
--- /dev/null
+++ b/CVE-2017-1000364.mm-larger-stack-guard-gap-between-vmas.patch
@@ -0,0 +1,883 @@
+From: Hugh Dickins <hughd@google.com>
+Date: Mon, 19 Jun 2017 04:03:24 -0700
+Subject: mm: larger stack guard gap, between vmas
+Origin: https://git.kernel.org/linus/1be7107fbe18eed3e319a6c3e83c78254b693acb
+
+Stack guard page is a useful feature to reduce a risk of stack smashing
+into a different mapping. We have been using a single page gap which
+is sufficient to prevent having stack adjacent to a different mapping.
+But this seems to be insufficient in the light of the stack usage in
+userspace. E.g. glibc uses as large as 64kB alloca() in many commonly
+used functions. Others use constructs liks gid_t buffer[NGROUPS_MAX]
+which is 256kB or stack strings with MAX_ARG_STRLEN.
+
+This will become especially dangerous for suid binaries and the default
+no limit for the stack size limit because those applications can be
+tricked to consume a large portion of the stack and a single glibc call
+could jump over the guard page. These attacks are not theoretical,
+unfortunatelly.
+
+Make those attacks less probable by increasing the stack guard gap
+to 1MB (on systems with 4k pages; but make it depend on the page size
+because systems with larger base pages might cap stack allocations in
+the PAGE_SIZE units) which should cover larger alloca() and VLA stack
+allocations. It is obviously not a full fix because the problem is
+somehow inherent, but it should reduce attack space a lot.
+
+One could argue that the gap size should be configurable from userspace,
+but that can be done later when somebody finds that the new 1MB is wrong
+for some special case applications. For now, add a kernel command line
+option (stack_guard_gap) to specify the stack gap size (in page units).
+
+Implementation wise, first delete all the old code for stack guard page:
+because although we could get away with accounting one extra page in a
+stack vma, accounting a larger gap can break userspace - case in point,
+a program run with "ulimit -S -v 20000" failed when the 1MB gap was
+counted for RLIMIT_AS; similar problems could come with RLIMIT_MLOCK
+and strict non-overcommit mode.
+
+Instead of keeping gap inside the stack vma, maintain the stack guard
+gap as a gap between vmas: using vm_start_gap() in place of vm_start
+(or vm_end_gap() in place of vm_end if VM_GROWSUP) in just those few
+places which need to respect the gap - mainly arch_get_unmapped_area(),
+and and the vma tree's subtree_gap support for that.
+
+Original-patch-by: Oleg Nesterov <oleg@redhat.com>
+Original-patch-by: Michal Hocko <mhocko@suse.com>
+Signed-off-by: Hugh Dickins <hughd@google.com>
+Acked-by: Michal Hocko <mhocko@suse.com>
+Tested-by: Helge Deller <deller@gmx.de> # parisc
+Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
+[bwh: Backported to 4.11: adjust context]
+---
+ Documentation/admin-guide/kernel-parameters.txt | 7 ++
+ arch/arc/mm/mmap.c | 2 +-
+ arch/arm/mm/mmap.c | 4 +-
+ arch/frv/mm/elf-fdpic.c | 2 +-
+ arch/mips/mm/mmap.c | 2 +-
+ arch/parisc/kernel/sys_parisc.c | 15 ++-
+ arch/powerpc/mm/hugetlbpage-radix.c | 2 +-
+ arch/powerpc/mm/mmap.c | 4 +-
+ arch/powerpc/mm/slice.c | 2 +-
+ arch/s390/mm/mmap.c | 4 +-
+ arch/sh/mm/mmap.c | 4 +-
+ arch/sparc/kernel/sys_sparc_64.c | 4 +-
+ arch/sparc/mm/hugetlbpage.c | 2 +-
+ arch/tile/mm/hugetlbpage.c | 2 +-
+ arch/x86/kernel/sys_x86_64.c | 4 +-
+ arch/x86/mm/hugetlbpage.c | 2 +-
+ arch/xtensa/kernel/syscall.c | 2 +-
+ fs/hugetlbfs/inode.c | 2 +-
+ fs/proc/task_mmu.c | 4 -
+ include/linux/mm.h | 53 ++++-----
+ mm/gup.c | 5 -
+ mm/memory.c | 38 ------
+ mm/mmap.c | 149 ++++++++++++++----------
+ 23 files changed, 152 insertions(+), 163 deletions(-)
+
+--- a/Documentation/admin-guide/kernel-parameters.txt
++++ b/Documentation/admin-guide/kernel-parameters.txt
+@@ -3779,6 +3779,13 @@
+ spia_pedr=
+ spia_peddr=
+
++ stack_guard_gap= [MM]
++ override the default stack gap protection. The value
++ is in page units and it defines how many pages prior
++ to (for stacks growing down) resp. after (for stacks
++ growing up) the main stack are reserved for no other
++ mapping. Default value is 256 pages.
++
+ stacktrace [FTRACE]
+ Enabled the stack tracer on boot up.
+
+--- a/arch/arc/mm/mmap.c
++++ b/arch/arc/mm/mmap.c
+@@ -65,7 +65,7 @@ arch_get_unmapped_area(struct file *filp
+
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+--- a/arch/arm/mm/mmap.c
++++ b/arch/arm/mm/mmap.c
+@@ -90,7 +90,7 @@ arch_get_unmapped_area(struct file *filp
+
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+@@ -141,7 +141,7 @@ arch_get_unmapped_area_topdown(struct fi
+ addr = PAGE_ALIGN(addr);
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+--- a/arch/frv/mm/elf-fdpic.c
++++ b/arch/frv/mm/elf-fdpic.c
+@@ -75,7 +75,7 @@ unsigned long arch_get_unmapped_area(str
+ addr = PAGE_ALIGN(addr);
+ vma = find_vma(current->mm, addr);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ goto success;
+ }
+
+--- a/arch/mips/mm/mmap.c
++++ b/arch/mips/mm/mmap.c
+@@ -93,7 +93,7 @@ static unsigned long arch_get_unmapped_a
+
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+--- a/arch/parisc/kernel/sys_parisc.c
++++ b/arch/parisc/kernel/sys_parisc.c
+@@ -90,7 +90,7 @@ unsigned long arch_get_unmapped_area(str
+ unsigned long len, unsigned long pgoff, unsigned long flags)
+ {
+ struct mm_struct *mm = current->mm;
+- struct vm_area_struct *vma;
++ struct vm_area_struct *vma, *prev;
+ unsigned long task_size = TASK_SIZE;
+ int do_color_align, last_mmap;
+ struct vm_unmapped_area_info info;
+@@ -117,9 +117,10 @@ unsigned long arch_get_unmapped_area(str
+ else
+ addr = PAGE_ALIGN(addr);
+
+- vma = find_vma(mm, addr);
++ vma = find_vma_prev(mm, addr, &prev);
+ if (task_size - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)) &&
++ (!prev || addr >= vm_end_gap(prev)))
+ goto found_addr;
+ }
+
+@@ -143,7 +144,7 @@ arch_get_unmapped_area_topdown(struct fi
+ const unsigned long len, const unsigned long pgoff,
+ const unsigned long flags)
+ {
+- struct vm_area_struct *vma;
++ struct vm_area_struct *vma, *prev;
+ struct mm_struct *mm = current->mm;
+ unsigned long addr = addr0;
+ int do_color_align, last_mmap;
+@@ -177,9 +178,11 @@ arch_get_unmapped_area_topdown(struct fi
+ addr = COLOR_ALIGN(addr, last_mmap, pgoff);
+ else
+ addr = PAGE_ALIGN(addr);
+- vma = find_vma(mm, addr);
++
++ vma = find_vma_prev(mm, addr, &prev);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)) &&
++ (!prev || addr >= vm_end_gap(prev)))
+ goto found_addr;
+ }
+
+--- a/arch/powerpc/mm/hugetlbpage-radix.c
++++ b/arch/powerpc/mm/hugetlbpage-radix.c
+@@ -65,7 +65,7 @@ radix__hugetlb_get_unmapped_area(struct
+ addr = ALIGN(addr, huge_page_size(h));
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+ /*
+--- a/arch/powerpc/mm/mmap.c
++++ b/arch/powerpc/mm/mmap.c
+@@ -107,7 +107,7 @@ radix__arch_get_unmapped_area(struct fil
+ addr = PAGE_ALIGN(addr);
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+@@ -143,7 +143,7 @@ radix__arch_get_unmapped_area_topdown(st
+ addr = PAGE_ALIGN(addr);
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+--- a/arch/powerpc/mm/slice.c
++++ b/arch/powerpc/mm/slice.c
+@@ -105,7 +105,7 @@ static int slice_area_is_free(struct mm_
+ if ((mm->task_size - len) < addr)
+ return 0;
+ vma = find_vma(mm, addr);
+- return (!vma || (addr + len) <= vma->vm_start);
++ return (!vma || (addr + len) <= vm_start_gap(vma));
+ }
+
+ static int slice_low_has_vma(struct mm_struct *mm, unsigned long slice)
+--- a/arch/s390/mm/mmap.c
++++ b/arch/s390/mm/mmap.c
+@@ -100,7 +100,7 @@ arch_get_unmapped_area(struct file *filp
+ addr = PAGE_ALIGN(addr);
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+@@ -138,7 +138,7 @@ arch_get_unmapped_area_topdown(struct fi
+ addr = PAGE_ALIGN(addr);
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+--- a/arch/sh/mm/mmap.c
++++ b/arch/sh/mm/mmap.c
+@@ -64,7 +64,7 @@ unsigned long arch_get_unmapped_area(str
+
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+@@ -114,7 +114,7 @@ arch_get_unmapped_area_topdown(struct fi
+
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+--- a/arch/sparc/kernel/sys_sparc_64.c
++++ b/arch/sparc/kernel/sys_sparc_64.c
+@@ -120,7 +120,7 @@ unsigned long arch_get_unmapped_area(str
+
+ vma = find_vma(mm, addr);
+ if (task_size - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+@@ -183,7 +183,7 @@ arch_get_unmapped_area_topdown(struct fi
+
+ vma = find_vma(mm, addr);
+ if (task_size - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+--- a/arch/sparc/mm/hugetlbpage.c
++++ b/arch/sparc/mm/hugetlbpage.c
+@@ -120,7 +120,7 @@ hugetlb_get_unmapped_area(struct file *f
+ addr = ALIGN(addr, huge_page_size(h));
+ vma = find_vma(mm, addr);
+ if (task_size - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+ if (mm->get_unmapped_area == arch_get_unmapped_area)
+--- a/arch/tile/mm/hugetlbpage.c
++++ b/arch/tile/mm/hugetlbpage.c
+@@ -233,7 +233,7 @@ unsigned long hugetlb_get_unmapped_area(
+ addr = ALIGN(addr, huge_page_size(h));
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+ if (current->mm->get_unmapped_area == arch_get_unmapped_area)
+--- a/arch/x86/kernel/sys_x86_64.c
++++ b/arch/x86/kernel/sys_x86_64.c
+@@ -141,7 +141,7 @@ arch_get_unmapped_area(struct file *filp
+ addr = PAGE_ALIGN(addr);
+ vma = find_vma(mm, addr);
+ if (end - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+@@ -184,7 +184,7 @@ arch_get_unmapped_area_topdown(struct fi
+ addr = PAGE_ALIGN(addr);
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+--- a/arch/x86/mm/hugetlbpage.c
++++ b/arch/x86/mm/hugetlbpage.c
+@@ -145,7 +145,7 @@ hugetlb_get_unmapped_area(struct file *f
+ addr = ALIGN(addr, huge_page_size(h));
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+ if (mm->get_unmapped_area == arch_get_unmapped_area)
+--- a/arch/xtensa/kernel/syscall.c
++++ b/arch/xtensa/kernel/syscall.c
+@@ -88,7 +88,7 @@ unsigned long arch_get_unmapped_area(str
+ /* At this point: (!vmm || addr < vmm->vm_end). */
+ if (TASK_SIZE - len < addr)
+ return -ENOMEM;
+- if (!vmm || addr + len <= vmm->vm_start)
++ if (!vmm || addr + len <= vm_start_gap(vmm))
+ return addr;
+ addr = vmm->vm_end;
+ if (flags & MAP_SHARED)
+--- a/fs/hugetlbfs/inode.c
++++ b/fs/hugetlbfs/inode.c
+@@ -200,7 +200,7 @@ hugetlb_get_unmapped_area(struct file *f
+ addr = ALIGN(addr, huge_page_size(h));
+ vma = find_vma(mm, addr);
+ if (TASK_SIZE - len >= addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)))
+ return addr;
+ }
+
+--- a/fs/proc/task_mmu.c
++++ b/fs/proc/task_mmu.c
+@@ -303,11 +303,7 @@ show_map_vma(struct seq_file *m, struct
+
+ /* We don't show the stack guard page in /proc/maps */
+ start = vma->vm_start;
+- if (stack_guard_page_start(vma, start))
+- start += PAGE_SIZE;
+ end = vma->vm_end;
+- if (stack_guard_page_end(vma, end))
+- end -= PAGE_SIZE;
+
+ seq_setwidth(m, 25 + sizeof(void *) * 6 - 1);
+ seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu ",
+--- a/include/linux/mm.h
++++ b/include/linux/mm.h
+@@ -1403,12 +1403,6 @@ int clear_page_dirty_for_io(struct page
+
+ int get_cmdline(struct task_struct *task, char *buffer, int buflen);
+
+-/* Is the vma a continuation of the stack vma above it? */
+-static inline int vma_growsdown(struct vm_area_struct *vma, unsigned long addr)
+-{
+- return vma && (vma->vm_end == addr) && (vma->vm_flags & VM_GROWSDOWN);
+-}
+-
+ static inline bool vma_is_anonymous(struct vm_area_struct *vma)
+ {
+ return !vma->vm_ops;
+@@ -1424,28 +1418,6 @@ bool vma_is_shmem(struct vm_area_struct
+ static inline bool vma_is_shmem(struct vm_area_struct *vma) { return false; }
+ #endif
+
+-static inline int stack_guard_page_start(struct vm_area_struct *vma,
+- unsigned long addr)
+-{
+- return (vma->vm_flags & VM_GROWSDOWN) &&
+- (vma->vm_start == addr) &&
+- !vma_growsdown(vma->vm_prev, addr);
+-}
+-
+-/* Is the vma a continuation of the stack vma below it? */
+-static inline int vma_growsup(struct vm_area_struct *vma, unsigned long addr)
+-{
+- return vma && (vma->vm_start == addr) && (vma->vm_flags & VM_GROWSUP);
+-}
+-
+-static inline int stack_guard_page_end(struct vm_area_struct *vma,
+- unsigned long addr)
+-{
+- return (vma->vm_flags & VM_GROWSUP) &&
+- (vma->vm_end == addr) &&
+- !vma_growsup(vma->vm_next, addr);
+-}
+-
+ int vma_is_stack_for_current(struct vm_area_struct *vma);
+
+ extern unsigned long move_page_tables(struct vm_area_struct *vma,
+@@ -2232,6 +2204,7 @@ void page_cache_async_readahead(struct a
+ pgoff_t offset,
+ unsigned long size);
+
++extern unsigned long stack_guard_gap;
+ /* Generic expand stack which grows the stack according to GROWS{UP,DOWN} */
+ extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
+
+@@ -2260,6 +2233,30 @@ static inline struct vm_area_struct * fi
+ return vma;
+ }
+
++static inline unsigned long vm_start_gap(struct vm_area_struct *vma)
++{
++ unsigned long vm_start = vma->vm_start;
++
++ if (vma->vm_flags & VM_GROWSDOWN) {
++ vm_start -= stack_guard_gap;
++ if (vm_start > vma->vm_start)
++ vm_start = 0;
++ }
++ return vm_start;
++}
++
++static inline unsigned long vm_end_gap(struct vm_area_struct *vma)
++{
++ unsigned long vm_end = vma->vm_end;
++
++ if (vma->vm_flags & VM_GROWSUP) {
++ vm_end += stack_guard_gap;
++ if (vm_end < vma->vm_end)
++ vm_end = -PAGE_SIZE;
++ }
++ return vm_end;
++}
++
+ static inline unsigned long vma_pages(struct vm_area_struct *vma)
+ {
+ return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+--- a/mm/gup.c
++++ b/mm/gup.c
+@@ -387,11 +387,6 @@ static int faultin_page(struct task_stru
+ /* mlock all present pages, but do not fault in new pages */
+ if ((*flags & (FOLL_POPULATE | FOLL_MLOCK)) == FOLL_MLOCK)
+ return -ENOENT;
+- /* For mm_populate(), just skip the stack guard page. */
+- if ((*flags & FOLL_POPULATE) &&
+- (stack_guard_page_start(vma, address) ||
+- stack_guard_page_end(vma, address + PAGE_SIZE)))
+- return -ENOENT;
+ if (*flags & FOLL_WRITE)
+ fault_flags |= FAULT_FLAG_WRITE;
+ if (*flags & FOLL_REMOTE)
+--- a/mm/memory.c
++++ b/mm/memory.c
+@@ -2855,40 +2855,6 @@ out_release:
+ }
+
+ /*
+- * This is like a special single-page "expand_{down|up}wards()",
+- * except we must first make sure that 'address{-|+}PAGE_SIZE'
+- * doesn't hit another vma.
+- */
+-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) {
+- struct vm_area_struct *prev = vma->vm_prev;
+-
+- /*
+- * Is there a mapping abutting this one below?
+- *
+- * That's only ok if it's the same stack mapping
+- * that has gotten split..
+- */
+- if (prev && prev->vm_end == address)
+- return prev->vm_flags & VM_GROWSDOWN ? 0 : -ENOMEM;
+-
+- return expand_downwards(vma, address - PAGE_SIZE);
+- }
+- if ((vma->vm_flags & VM_GROWSUP) && address + PAGE_SIZE == vma->vm_end) {
+- struct vm_area_struct *next = vma->vm_next;
+-
+- /* As VM_GROWSDOWN but s/below/above/ */
+- if (next && next->vm_start == address + PAGE_SIZE)
+- return next->vm_flags & VM_GROWSUP ? 0 : -ENOMEM;
+-
+- return expand_upwards(vma, address + PAGE_SIZE);
+- }
+- 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.
+@@ -2904,10 +2870,6 @@ static int do_anonymous_page(struct vm_f
+ if (vma->vm_flags & VM_SHARED)
+ return VM_FAULT_SIGBUS;
+
+- /* Check if we need to add a guard page to the stack */
+- if (check_stack_guard_page(vma, vmf->address) < 0)
+- return VM_FAULT_SIGSEGV;
+-
+ /*
+ * Use pte_alloc() instead of pte_alloc_map(). We can't run
+ * pte_offset_map() on pmds where a huge pmd might be created
+--- a/mm/mmap.c
++++ b/mm/mmap.c
+@@ -183,6 +183,7 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
+ unsigned long retval;
+ unsigned long newbrk, oldbrk;
+ struct mm_struct *mm = current->mm;
++ struct vm_area_struct *next;
+ unsigned long min_brk;
+ bool populate;
+ LIST_HEAD(uf);
+@@ -229,7 +230,8 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
+ }
+
+ /* Check against existing mmap mappings. */
+- if (find_vma_intersection(mm, oldbrk, newbrk+PAGE_SIZE))
++ next = find_vma(mm, oldbrk);
++ if (next && newbrk + PAGE_SIZE > vm_start_gap(next))
+ goto out;
+
+ /* Ok, looks good - let it rip. */
+@@ -253,10 +255,22 @@ out:
+
+ static long vma_compute_subtree_gap(struct vm_area_struct *vma)
+ {
+- unsigned long max, subtree_gap;
+- max = vma->vm_start;
+- if (vma->vm_prev)
+- max -= vma->vm_prev->vm_end;
++ unsigned long max, prev_end, subtree_gap;
++
++ /*
++ * Note: in the rare case of a VM_GROWSDOWN above a VM_GROWSUP, we
++ * allow two stack_guard_gaps between them here, and when choosing
++ * an unmapped area; whereas when expanding we only require one.
++ * That's a little inconsistent, but keeps the code here simpler.
++ */
++ max = vm_start_gap(vma);
++ if (vma->vm_prev) {
++ prev_end = vm_end_gap(vma->vm_prev);
++ if (max > prev_end)
++ max -= prev_end;
++ else
++ max = 0;
++ }
+ if (vma->vm_rb.rb_left) {
+ subtree_gap = rb_entry(vma->vm_rb.rb_left,
+ struct vm_area_struct, vm_rb)->rb_subtree_gap;
+@@ -352,7 +366,7 @@ static void validate_mm(struct mm_struct
+ anon_vma_unlock_read(anon_vma);
+ }
+
+- highest_address = vma->vm_end;
++ highest_address = vm_end_gap(vma);
+ vma = vma->vm_next;
+ i++;
+ }
+@@ -541,7 +555,7 @@ void __vma_link_rb(struct mm_struct *mm,
+ if (vma->vm_next)
+ vma_gap_update(vma->vm_next);
+ else
+- mm->highest_vm_end = vma->vm_end;
++ mm->highest_vm_end = vm_end_gap(vma);
+
+ /*
+ * vma->vm_prev wasn't known when we followed the rbtree to find the
+@@ -856,7 +870,7 @@ again:
+ vma_gap_update(vma);
+ if (end_changed) {
+ if (!next)
+- mm->highest_vm_end = end;
++ mm->highest_vm_end = vm_end_gap(vma);
+ else if (!adjust_next)
+ vma_gap_update(next);
+ }
+@@ -941,7 +955,7 @@ again:
+ * mm->highest_vm_end doesn't need any update
+ * in remove_next == 1 case.
+ */
+- VM_WARN_ON(mm->highest_vm_end != end);
++ VM_WARN_ON(mm->highest_vm_end != vm_end_gap(vma));
+ }
+ }
+ if (insert && file)
+@@ -1787,7 +1801,7 @@ unsigned long unmapped_area(struct vm_un
+
+ while (true) {
+ /* Visit left subtree if it looks promising */
+- gap_end = vma->vm_start;
++ gap_end = vm_start_gap(vma);
+ if (gap_end >= low_limit && vma->vm_rb.rb_left) {
+ struct vm_area_struct *left =
+ rb_entry(vma->vm_rb.rb_left,
+@@ -1798,7 +1812,7 @@ unsigned long unmapped_area(struct vm_un
+ }
+ }
+
+- gap_start = vma->vm_prev ? vma->vm_prev->vm_end : 0;
++ gap_start = vma->vm_prev ? vm_end_gap(vma->vm_prev) : 0;
+ check_current:
+ /* Check if current node has a suitable gap */
+ if (gap_start > high_limit)
+@@ -1825,8 +1839,8 @@ check_current:
+ vma = rb_entry(rb_parent(prev),
+ struct vm_area_struct, vm_rb);
+ if (prev == vma->vm_rb.rb_left) {
+- gap_start = vma->vm_prev->vm_end;
+- gap_end = vma->vm_start;
++ gap_start = vm_end_gap(vma->vm_prev);
++ gap_end = vm_start_gap(vma);
+ goto check_current;
+ }
+ }
+@@ -1890,7 +1904,7 @@ unsigned long unmapped_area_topdown(stru
+
+ while (true) {
+ /* Visit right subtree if it looks promising */
+- gap_start = vma->vm_prev ? vma->vm_prev->vm_end : 0;
++ gap_start = vma->vm_prev ? vm_end_gap(vma->vm_prev) : 0;
+ if (gap_start <= high_limit && vma->vm_rb.rb_right) {
+ struct vm_area_struct *right =
+ rb_entry(vma->vm_rb.rb_right,
+@@ -1903,7 +1917,7 @@ unsigned long unmapped_area_topdown(stru
+
+ check_current:
+ /* Check if current node has a suitable gap */
+- gap_end = vma->vm_start;
++ gap_end = vm_start_gap(vma);
+ if (gap_end < low_limit)
+ return -ENOMEM;
+ if (gap_start <= high_limit && gap_end - gap_start >= length)
+@@ -1929,7 +1943,7 @@ check_current:
+ struct vm_area_struct, vm_rb);
+ if (prev == vma->vm_rb.rb_right) {
+ gap_start = vma->vm_prev ?
+- vma->vm_prev->vm_end : 0;
++ vm_end_gap(vma->vm_prev) : 0;
+ goto check_current;
+ }
+ }
+@@ -1967,7 +1981,7 @@ arch_get_unmapped_area(struct file *filp
+ unsigned long len, unsigned long pgoff, unsigned long flags)
+ {
+ struct mm_struct *mm = current->mm;
+- struct vm_area_struct *vma;
++ struct vm_area_struct *vma, *prev;
+ struct vm_unmapped_area_info info;
+
+ if (len > TASK_SIZE - mmap_min_addr)
+@@ -1978,9 +1992,10 @@ arch_get_unmapped_area(struct file *filp
+
+ if (addr) {
+ addr = PAGE_ALIGN(addr);
+- vma = find_vma(mm, addr);
++ vma = find_vma_prev(mm, addr, &prev);
+ if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)) &&
++ (!prev || addr >= vm_end_gap(prev)))
+ return addr;
+ }
+
+@@ -2003,7 +2018,7 @@ arch_get_unmapped_area_topdown(struct fi
+ const unsigned long len, const unsigned long pgoff,
+ const unsigned long flags)
+ {
+- struct vm_area_struct *vma;
++ struct vm_area_struct *vma, *prev;
+ struct mm_struct *mm = current->mm;
+ unsigned long addr = addr0;
+ struct vm_unmapped_area_info info;
+@@ -2018,9 +2033,10 @@ arch_get_unmapped_area_topdown(struct fi
+ /* requesting a specific address */
+ if (addr) {
+ addr = PAGE_ALIGN(addr);
+- vma = find_vma(mm, addr);
++ vma = find_vma_prev(mm, addr, &prev);
+ if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
+- (!vma || addr + len <= vma->vm_start))
++ (!vma || addr + len <= vm_start_gap(vma)) &&
++ (!prev || addr >= vm_end_gap(prev)))
+ return addr;
+ }
+
+@@ -2155,21 +2171,19 @@ find_vma_prev(struct mm_struct *mm, unsi
+ * update accounting. This is shared with both the
+ * grow-up and grow-down cases.
+ */
+-static int acct_stack_growth(struct vm_area_struct *vma, unsigned long size, unsigned long grow)
++static int acct_stack_growth(struct vm_area_struct *vma,
++ unsigned long size, unsigned long grow)
+ {
+ struct mm_struct *mm = vma->vm_mm;
+ struct rlimit *rlim = current->signal->rlim;
+- unsigned long new_start, actual_size;
++ unsigned long new_start;
+
+ /* address space limit tests */
+ if (!may_expand_vm(mm, vma->vm_flags, grow))
+ return -ENOMEM;
+
+ /* Stack limit test */
+- actual_size = size;
+- if (size && (vma->vm_flags & (VM_GROWSUP | VM_GROWSDOWN)))
+- actual_size -= PAGE_SIZE;
+- if (actual_size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur))
++ if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur))
+ return -ENOMEM;
+
+ /* mlock limit tests */
+@@ -2207,17 +2221,30 @@ static int acct_stack_growth(struct vm_a
+ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
+ {
+ struct mm_struct *mm = vma->vm_mm;
++ struct vm_area_struct *next;
++ unsigned long gap_addr;
+ int error = 0;
+
+ if (!(vma->vm_flags & VM_GROWSUP))
+ return -EFAULT;
+
+ /* Guard against wrapping around to address 0. */
+- if (address < PAGE_ALIGN(address+4))
+- address = PAGE_ALIGN(address+4);
+- else
++ address &= PAGE_MASK;
++ address += PAGE_SIZE;
++ if (!address)
+ return -ENOMEM;
+
++ /* Enforce stack_guard_gap */
++ gap_addr = address + stack_guard_gap;
++ if (gap_addr < address)
++ return -ENOMEM;
++ next = vma->vm_next;
++ if (next && next->vm_start < gap_addr) {
++ if (!(next->vm_flags & VM_GROWSUP))
++ return -ENOMEM;
++ /* Check that both stack segments have the same anon_vma? */
++ }
++
+ /* We must make sure the anon_vma is allocated. */
+ if (unlikely(anon_vma_prepare(vma)))
+ return -ENOMEM;
+@@ -2261,7 +2288,7 @@ int expand_upwards(struct vm_area_struct
+ if (vma->vm_next)
+ vma_gap_update(vma->vm_next);
+ else
+- mm->highest_vm_end = address;
++ mm->highest_vm_end = vm_end_gap(vma);
+ spin_unlock(&mm->page_table_lock);
+
+ perf_event_mmap(vma);
+@@ -2282,6 +2309,8 @@ int expand_downwards(struct vm_area_stru
+ unsigned long address)
+ {
+ struct mm_struct *mm = vma->vm_mm;
++ struct vm_area_struct *prev;
++ unsigned long gap_addr;
+ int error;
+
+ address &= PAGE_MASK;
+@@ -2289,6 +2318,17 @@ int expand_downwards(struct vm_area_stru
+ if (error)
+ return error;
+
++ /* Enforce stack_guard_gap */
++ gap_addr = address - stack_guard_gap;
++ if (gap_addr > address)
++ return -ENOMEM;
++ prev = vma->vm_prev;
++ if (prev && prev->vm_end > gap_addr) {
++ if (!(prev->vm_flags & VM_GROWSDOWN))
++ return -ENOMEM;
++ /* Check that both stack segments have the same anon_vma? */
++ }
++
+ /* We must make sure the anon_vma is allocated. */
+ if (unlikely(anon_vma_prepare(vma)))
+ return -ENOMEM;
+@@ -2343,28 +2383,25 @@ int expand_downwards(struct vm_area_stru
+ return error;
+ }
+
+-/*
+- * Note how expand_stack() refuses to expand the stack all the way to
+- * abut the next virtual mapping, *unless* that mapping itself is also
+- * a stack mapping. We want to leave room for a guard page, after all
+- * (the guard page itself is not added here, that is done by the
+- * actual page faulting logic)
+- *
+- * This matches the behavior of the guard page logic (see mm/memory.c:
+- * check_stack_guard_page()), which only allows the guard page to be
+- * removed under these circumstances.
+- */
++/* enforced gap between the expanding stack and other mappings. */
++unsigned long stack_guard_gap = 256UL<<PAGE_SHIFT;
++
++static int __init cmdline_parse_stack_guard_gap(char *p)
++{
++ unsigned long val;
++ char *endptr;
++
++ val = simple_strtoul(p, &endptr, 10);
++ if (!*endptr)
++ stack_guard_gap = val << PAGE_SHIFT;
++
++ return 0;
++}
++__setup("stack_guard_gap=", cmdline_parse_stack_guard_gap);
++
+ #ifdef CONFIG_STACK_GROWSUP
+ int expand_stack(struct vm_area_struct *vma, unsigned long address)
+ {
+- struct vm_area_struct *next;
+-
+- address &= PAGE_MASK;
+- next = vma->vm_next;
+- if (next && next->vm_start == address + PAGE_SIZE) {
+- if (!(next->vm_flags & VM_GROWSUP))
+- return -ENOMEM;
+- }
+ return expand_upwards(vma, address);
+ }
+
+@@ -2386,14 +2423,6 @@ find_extend_vma(struct mm_struct *mm, un
+ #else
+ int expand_stack(struct vm_area_struct *vma, unsigned long address)
+ {
+- struct vm_area_struct *prev;
+-
+- address &= PAGE_MASK;
+- prev = vma->vm_prev;
+- if (prev && prev->vm_end == address) {
+- if (!(prev->vm_flags & VM_GROWSDOWN))
+- return -ENOMEM;
+- }
+ return expand_downwards(vma, address);
+ }
+
+@@ -2491,7 +2520,7 @@ detach_vmas_to_be_unmapped(struct mm_str
+ vma->vm_prev = prev;
+ vma_gap_update(vma);
+ } else
+- mm->highest_vm_end = prev ? prev->vm_end : 0;
++ mm->highest_vm_end = prev ? vm_end_gap(prev) : 0;
+ tail_vma->vm_next = NULL;
+
+ /* Kill the cache */