[linux-yocto] [PATCH 1/3] mm: larger stack guard gap, between vmas
Bruce Ashfield
bruce.ashfield at windriver.com
Tue Aug 15 12:41:53 PDT 2017
If there was a 0/N for this series, I managed to miss it.
What tree is this for ? And what issue is it fixing ?
Bruce
On 2017-08-14 10:51 PM, jianchuan.wang at windriver.com wrote:
> From: Hugh Dickins <hughd at google.com>
>
> 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 at redhat.com>
> Original-patch-by: Michal Hocko <mhocko at suse.com>
> Signed-off-by: Hugh Dickins <hughd at google.com>
> Acked-by: Michal Hocko <mhocko at suse.com>
> Tested-by: Helge Deller <deller at gmx.de> # parisc
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> [wt: backport to 4.11: adjust context]
> [wt: backport to 4.9: adjust context ; kernel doc was not in admin-guide]
> Signed-off-by: Willy Tarreau <w at 1wt.eu>
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> Signed-off-by: Paul Gortmaker <paul.gortmaker at windriver.com>
> Signed-off-by: Jianchuan Wang <jianchuan.wang at windriver.com>
> ---
> 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/memory.c.rej | 10 ---
> mm/mmap.c | 148 ++++++++++++++++++++++--------------
> 23 files changed, 145 insertions(+), 172 deletions(-)
> delete mode 100644 mm/memory.c.rej
>
> diff --git a/arch/arc/mm/mmap.c b/arch/arc/mm/mmap.c
> index 2e06d56..cf4ae69 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 66353ca..641334e 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 836f147..efa59f1 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 d08ea3f..a44052c 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 bf32941..5fb3f0e 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/hugetlbpage-radix.c b/arch/powerpc/mm/hugetlbpage-radix.c
> index 35254a6..a2b2d97 100644
> --- a/arch/powerpc/mm/hugetlbpage-radix.c
> +++ b/arch/powerpc/mm/hugetlbpage-radix.c
> @@ -65,7 +65,7 @@ radix__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/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
> index 2f1e443..5bc2845 100644
> --- a/arch/powerpc/mm/mmap.c
> +++ b/arch/powerpc/mm/mmap.c
> @@ -106,7 +106,7 @@ radix__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;
> }
>
> @@ -142,7 +142,7 @@ radix__arch_get_unmapped_area_topdown(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;
> }
>
> diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
> index 2b27458..c4d5c9c 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 eb9df28..812368f 100644
> --- a/arch/s390/mm/mmap.c
> +++ b/arch/s390/mm/mmap.c
> @@ -98,7 +98,7 @@ 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;
> }
>
> @@ -136,7 +136,7 @@ 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 6777177..7df7d59 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 884c703..f39dd87 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 988acc8..58cde8d 100644
> --- a/arch/sparc/mm/hugetlbpage.c
> +++ b/arch/sparc/mm/hugetlbpage.c
> @@ -116,7 +116,7 @@ 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 77ceaa3..67508b2 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 a55ed63..1119414 100644
> --- a/arch/x86/kernel/sys_x86_64.c
> +++ b/arch/x86/kernel/sys_x86_64.c
> @@ -140,7 +140,7 @@ 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;
> }
>
> @@ -183,7 +183,7 @@ 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 2ae8584..fe342e8 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 d3fd100..dceb0ee 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 54de77e..19a787e 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 52049b5..5e6bab5 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -302,11 +302,7 @@ 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 3978a35..705bf34 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1366,39 +1366,11 @@ 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_current(struct vm_area_struct *vma);
>
> extern unsigned long move_page_tables(struct vm_area_struct *vma,
> @@ -2139,6 +2111,7 @@ 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);
>
> @@ -2167,6 +2140,30 @@ 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 5531555..2c9f075 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -370,11 +370,6 @@ 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 (*flags & FOLL_REMOTE)
> diff --git a/mm/memory.c b/mm/memory.c
> index 83d7132..286d00f 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2715,40 +2715,6 @@ int do_swap_page(struct vm_fault *vmf)
> }
>
> /*
> - * 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.
> @@ -2764,10 +2730,6 @@ static int do_anonymous_page(struct vm_fault *vmf)
> 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
> diff --git a/mm/memory.c.rej b/mm/memory.c.rej
> deleted file mode 100644
> index 83fc5a5..0000000
> --- a/mm/memory.c.rej
> +++ /dev/null
> @@ -1,10 +0,0 @@
> -diff a/mm/memory.c b/mm/memory.c (rejected hunks)
> -@@ -2117,7 +2117,7 @@ static inline int wp_page_reuse(struct fault_env *fe, pte_t orig_pte,
> - }
> -
> - if (!page_mkwrite)
> -- file_update_time(vma->vm_file);
> -+ vma_file_update_time(vma);
> - }
> -
> - return VM_FAULT_WRITE;
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 4b3a2aa..945ff3b 100644
> --- 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;
>
> @@ -228,7 +229,8 @@ 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. */
> @@ -251,10 +253,22 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
>
> 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;
> @@ -350,7 +364,7 @@ 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++;
> }
> @@ -539,7 +553,7 @@ 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
> @@ -854,7 +868,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
> 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);
> }
> @@ -940,6 +954,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
> * in remove_next == 1 case.
> */
> VM_WARN_ON(mm->highest_vm_end != end);
> + mm->highest_vm_end = vm_end_gap(vma);
> }
> }
> if (insert && file)
> @@ -1783,7 +1798,7 @@ 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,
> @@ -1794,7 +1809,7 @@ 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)
> @@ -1821,8 +1836,8 @@ unsigned long unmapped_area(struct vm_unmapped_area_info *info)
> 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;
> }
> }
> @@ -1886,7 +1901,7 @@ 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,
> @@ -1899,7 +1914,7 @@ 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)
> @@ -1925,7 +1940,7 @@ unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
> 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;
> }
> }
> @@ -1963,7 +1978,7 @@ 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)
> @@ -1974,9 +1989,10 @@ 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;
> }
>
> @@ -1999,7 +2015,7 @@ 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;
> @@ -2014,9 +2030,10 @@ 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;
> }
>
> @@ -2151,21 +2168,19 @@ 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, 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 */
> @@ -2203,17 +2218,30 @@ 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;
> @@ -2257,7 +2285,7 @@ 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);
> @@ -2278,6 +2306,8 @@ 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;
> @@ -2285,6 +2315,17 @@ 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;
> @@ -2339,28 +2380,25 @@ 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);
> }
>
> @@ -2382,14 +2420,6 @@ 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);
> }
>
> @@ -2487,7 +2517,7 @@ 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 */
>
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