Backport fix for CVE-2017-1000364 to linux-yocto-4.4

Backport of upstream fixes from 4.4 kernel branch to linux-yocto:
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?h=linux-4.4.y&id=4b359430674caa2c98d0049a6941f157d2a33741
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?h=linux-4.4.y&id=f41512c6acb71c63cf4e3bd50934365ae2a23891
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?h=linux-4.4.y&id=1f2284fac2180d7a9442c796d9755e3ce7ab0bd9

Bug-AGL: SPEC-705 SPEC-706

Change-Id: I8f180d6d58d985ca7186638015a57d3d836a9a61
Signed-off-by: Jan-Simon Möller <jsmoeller@linuxfoundation.org>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/9861
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-boot-test: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Reviewed-by: Stéphane Desneux <stephane.desneux@iot.bzh>

1 files changed, 900 insertions, 0 deletions

diff --git a/meta-agl-bsp/recipes-kernel/linux/linux-yocto/0001-mm-larger-stack-guard-gap-between-vmas.patch b/meta-agl-bsp/recipes-kernel/linux/linux-yocto/0001-mm-larger-stack-guard-gap-between-vmas.patch
new file mode 100644
index 000000000..2e1b91402
--- /dev/null
+++ b/meta-agl-bsp/recipes-kernel/linux/linux-yocto/0001-mm-larger-stack-guard-gap-between-vmas.patch
@@ -0,0 +1,900 @@
+From 39af74787812c006d38499eb2f2802318075c33b Mon Sep 17 00:00:00 2001
+From: Hugh Dickins <hughd@google.com>
+Date: Mon, 19 Jun 2017 04:03:24 -0700
+Subject: [PATCH 1/3] mm: larger stack guard gap, between vmas
+
+commit 1be7107fbe18eed3e319a6c3e83c78254b693acb upstream.
+
+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>
+[wt: backport to 4.11: adjust context]
+[wt: backport to 4.9: adjust context ; kernel doc was not in admin-guide]
+[wt: backport to 4.4: adjust context ; drop ppc hugetlb_radix changes]
+Signed-off-by: Willy Tarreau <w@1wt.eu>
+[gkh: minor build fixes for 4.4]
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ Documentation/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/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 +++++++++++++++++++++---------------
+ 21 files changed, 149 insertions(+), 160 deletions(-)
+
+diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
+index 36f0f8d80922..1410e9231f93 100644
+--- a/Documentation/kernel-parameters.txt
++++ b/Documentation/kernel-parameters.txt
+@@ -3576,6 +3576,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
+ 	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.
+ 
+diff --git a/arch/arc/mm/mmap.c b/arch/arc/mm/mmap.c
+index 2e06d56e987b..cf4ae6958240 100644
+--- a/arch/arc/mm/mmap.c
++++ b/arch/arc/mm/mmap.c
+@@ -64,7 +64,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long 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;
+ 	}
+ 
+diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
+index 407dc786583a..c469c0665752 100644
+--- a/arch/arm/mm/mmap.c
++++ b/arch/arm/mm/mmap.c
+@@ -89,7 +89,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long 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;
+ 	}
+ 
+@@ -140,7 +140,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
+ 			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;
+ 	}
+ 
+diff --git a/arch/frv/mm/elf-fdpic.c b/arch/frv/mm/elf-fdpic.c
+index 836f14707a62..efa59f1f8022 100644
+--- a/arch/frv/mm/elf-fdpic.c
++++ b/arch/frv/mm/elf-fdpic.c
+@@ -74,7 +74,7 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, unsi
+ 		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;
+ 	}
+ 
+diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
+index 5c81fdd032c3..025cb31aa0a2 100644
+--- a/arch/mips/mm/mmap.c
++++ b/arch/mips/mm/mmap.c
+@@ -92,7 +92,7 @@ static unsigned long arch_get_unmapped_area_common(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;
+ 	}
+ 
+diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c
+index 5aba01ac457f..4dda73c44fee 100644
+--- a/arch/parisc/kernel/sys_parisc.c
++++ b/arch/parisc/kernel/sys_parisc.c
+@@ -88,7 +88,7 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
+ 		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;
+@@ -115,9 +115,10 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
+ 		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;
+ 	}
+ 
+@@ -141,7 +142,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
+ 			  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;
+@@ -175,9 +176,11 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
+ 			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;
+ 	}
+ 
+diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
+index 0f432a702870..6ad12b244770 100644
+--- a/arch/powerpc/mm/slice.c
++++ b/arch/powerpc/mm/slice.c
+@@ -105,7 +105,7 @@ static int slice_area_is_free(struct mm_struct *mm, unsigned long addr,
+ 	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)
+diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
+index f2b6b1d9c804..126c4a9b9bf9 100644
+--- a/arch/s390/mm/mmap.c
++++ b/arch/s390/mm/mmap.c
+@@ -97,7 +97,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
+ 		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;
+ 	}
+ 
+@@ -135,7 +135,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
+ 		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;
+ 	}
+ 
+diff --git a/arch/sh/mm/mmap.c b/arch/sh/mm/mmap.c
+index 6777177807c2..7df7d5944188 100644
+--- a/arch/sh/mm/mmap.c
++++ b/arch/sh/mm/mmap.c
+@@ -63,7 +63,7 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long 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;
+ 	}
+ 
+@@ -113,7 +113,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
+ 
+ 		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;
+ 	}
+ 
+diff --git a/arch/sparc/kernel/sys_sparc_64.c b/arch/sparc/kernel/sys_sparc_64.c
+index c690c8e16a96..7f0f7c01b297 100644
+--- a/arch/sparc/kernel/sys_sparc_64.c
++++ b/arch/sparc/kernel/sys_sparc_64.c
+@@ -118,7 +118,7 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, unsi
+ 
+ 		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;
+ 	}
+ 
+@@ -181,7 +181,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
+ 
+ 		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;
+ 	}
+ 
+diff --git a/arch/sparc/mm/hugetlbpage.c b/arch/sparc/mm/hugetlbpage.c
+index 364d093f46c6..4c462ba89597 100644
+--- a/arch/sparc/mm/hugetlbpage.c
++++ b/arch/sparc/mm/hugetlbpage.c
+@@ -115,7 +115,7 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
+ 		addr = ALIGN(addr, HPAGE_SIZE);
+ 		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)
+diff --git a/arch/tile/mm/hugetlbpage.c b/arch/tile/mm/hugetlbpage.c
+index c034dc3fe2d4..c97ee6c7f949 100644
+--- a/arch/tile/mm/hugetlbpage.c
++++ b/arch/tile/mm/hugetlbpage.c
+@@ -232,7 +232,7 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
+ 		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)
+diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
+index 10e0272d789a..136ad7c1ce7b 100644
+--- a/arch/x86/kernel/sys_x86_64.c
++++ b/arch/x86/kernel/sys_x86_64.c
+@@ -143,7 +143,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
+ 		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;
+ 	}
+ 
+@@ -186,7 +186,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
+ 		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;
+ 	}
+ 
+diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
+index 42982b26e32b..39bdaf3ac44a 100644
+--- a/arch/x86/mm/hugetlbpage.c
++++ b/arch/x86/mm/hugetlbpage.c
+@@ -144,7 +144,7 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
+ 		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)
+diff --git a/arch/xtensa/kernel/syscall.c b/arch/xtensa/kernel/syscall.c
+index 83cf49685373..3aaaae18417c 100644
+--- a/arch/xtensa/kernel/syscall.c
++++ b/arch/xtensa/kernel/syscall.c
+@@ -87,7 +87,7 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
+ 		/* 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)
+diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
+index 595ebdb41846..a17da8b57fc6 100644
+--- a/fs/hugetlbfs/inode.c
++++ b/fs/hugetlbfs/inode.c
+@@ -191,7 +191,7 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
+ 		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;
+ 	}
+ 
+diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
+index 728641214fe2..a5ee9d59884e 100644
+--- a/fs/proc/task_mmu.c
++++ b/fs/proc/task_mmu.c
+@@ -298,11 +298,7 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma, int is_pid)
+ 
+ 	/* 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 ",
+diff --git a/include/linux/mm.h b/include/linux/mm.h
+index 11db295a4a95..a04fec1ef048 100644
+--- a/include/linux/mm.h
++++ b/include/linux/mm.h
+@@ -1300,39 +1300,11 @@ int clear_page_dirty_for_io(struct page *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;
+ }
+ 
+-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_task(struct vm_area_struct *vma, struct task_struct *t);
+ 
+ extern unsigned long move_page_tables(struct vm_area_struct *vma,
+@@ -2034,6 +2006,7 @@ void page_cache_async_readahead(struct address_space *mapping,
+ 				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);
+ 
+@@ -2062,6 +2035,30 @@ static inline struct vm_area_struct * find_vma_intersection(struct mm_struct * m
+ 	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;
+diff --git a/mm/gup.c b/mm/gup.c
+index 4b0b7e7d1136..b599526db9f7 100644
+--- a/mm/gup.c
++++ b/mm/gup.c
+@@ -312,11 +312,6 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
+ 	/* 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 (nonblocking)
+diff --git a/mm/memory.c b/mm/memory.c
+index 278c33c72086..16390b50a564 100644
+--- a/mm/memory.c
++++ b/mm/memory.c
+@@ -2662,40 +2662,6 @@ 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.
+@@ -2715,10 +2681,6 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
+ 	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, address) < 0)
+-		return VM_FAULT_SIGSEGV;
+-
+ 	/* Use the zero-page for reads */
+ 	if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm)) {
+ 		entry = pte_mkspecial(pfn_pte(my_zero_pfn(address),
+diff --git a/mm/mmap.c b/mm/mmap.c
+index 550cd934497f..7567494e0dfa 100644
+--- a/mm/mmap.c
++++ b/mm/mmap.c
+@@ -288,6 +288,7 @@ 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;
+ 
+@@ -332,7 +333,8 @@ 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. */
+@@ -355,10 +357,22 @@ 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;
+@@ -451,7 +465,7 @@ static void validate_mm(struct mm_struct *mm)
+ 			anon_vma_unlock_read(anon_vma);
+ 		}
+ 
+-		highest_address = vma->vm_end;
++		highest_address = vm_end_gap(vma);
+ 		vma = vma->vm_next;
+ 		i++;
+ 	}
+@@ -620,7 +634,7 @@ void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
+ 	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
+@@ -866,7 +880,7 @@ again:			remove_next = 1 + (end > next->vm_end);
+ 			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);
+ 		}
+@@ -909,7 +923,7 @@ again:			remove_next = 1 + (end > next->vm_end);
+ 		else if (next)
+ 			vma_gap_update(next);
+ 		else
+-			mm->highest_vm_end = end;
++			VM_WARN_ON(mm->highest_vm_end != vm_end_gap(vma));
+ 	}
+ 	if (insert && file)
+ 		uprobe_mmap(insert);
+@@ -1741,7 +1755,7 @@ unsigned long unmapped_area(struct vm_unmapped_area_info *info)
+ 
+ 	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,
+@@ -1752,7 +1766,7 @@ unsigned long unmapped_area(struct vm_unmapped_area_info *info)
+ 			}
+ 		}
+ 
+-		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)
+@@ -1779,8 +1793,8 @@ 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;
+ 			}
+ 		}
+@@ -1844,7 +1858,7 @@ unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
+ 
+ 	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,
+@@ -1857,7 +1871,7 @@ unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
+ 
+ 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)
+@@ -1883,7 +1897,7 @@ 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;
+ 			}
+ 		}
+@@ -1921,7 +1935,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
+ 		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)
+@@ -1932,9 +1946,10 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
+ 
+ 	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;
+ 	}
+ 
+@@ -1957,7 +1972,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
+ 			  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;
+@@ -1972,9 +1987,10 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
+ 	/* 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;
+ 	}
+ 
+@@ -2099,21 +2115,19 @@ find_vma_prev(struct mm_struct *mm, unsigned long addr,
+  * 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, 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 */
+@@ -2151,17 +2165,30 @@ static int acct_stack_growth(struct vm_area_struct *vma, unsigned long size, uns
+ 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;
+@@ -2206,7 +2233,7 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
+ 				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);
+@@ -2227,6 +2254,8 @@ int expand_downwards(struct vm_area_struct *vma,
+ 				   unsigned long address)
+ {
+ 	struct mm_struct *mm = vma->vm_mm;
++	struct vm_area_struct *prev;
++	unsigned long gap_addr;
+ 	int error;
+ 
+ 	address &= PAGE_MASK;
+@@ -2234,6 +2263,17 @@ int expand_downwards(struct vm_area_struct *vma,
+ 	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;
+@@ -2289,28 +2329,25 @@ int expand_downwards(struct vm_area_struct *vma,
+ 	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);
+ }
+ 
+@@ -2332,14 +2369,6 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr)
+ #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);
+ }
+ 
+@@ -2437,7 +2466,7 @@ detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
+ 		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 */
+-- 
+2.12.3
+