Patch "mm: larger stack guard gap, between vmas" has been added to the 4.4-stable tree

PATCH [email protected] 1 participant 1 message Jun 19, 2017

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Stable branch Memory management Documentation Arm (32-bit) +16 more subsystems

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2017-06-19 15:10 UTC #0 lore raw

This is a note to let you know that I've just added the patch titled

mm: larger stack guard gap, between vmas

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-larger-stack-guard-gap-between-vmas.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 1be7107fbe18eed3e319a6c3e83c78254b693acb Mon Sep 17 00:00:00 2001

From: Hugh Dickins <[email protected]>
Date: Mon, 19 Jun 2017 04:03:24 -0700
Subject: mm: larger stack guard gap, between vmas

From: Hugh Dickins <[email protected]>

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 <[email protected]>

Original-patch-by Michal Hocko <[email protected]>

Signed-off-by Hugh Dickins <[email protected]>

Acked-by Michal Hocko <[email protected]>

Tested-by Helge Deller <[email protected]> # parisc

Signed-off-by Linus Torvalds <[email protected]>

[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 <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 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                  |   55 ++++++-------
 mm/gup.c                            |    5 -
 mm/memory.c                         |   38 ---------
 mm/mmap.c                           |  147 +++++++++++++++++++++---------------
 21 files changed, 148 insertions(+), 161 deletions(-)

Documentation/kernel-parameters.txt +7 -0

@@ -3580,6 +3580,13 @@ bytes respectively. Such letter suffixes
 	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.

arch/arc/mm/mmap.c +1 -1

@@ -64,7 +64,7 @@ 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;
 	}

arch/arm/mm/mmap.c +2 -2

@@ -89,7 +89,7 @@ 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;
 	}

@@ -140,7 +140,7 @@ 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;
 	}

arch/frv/mm/elf-fdpic.c +1 -1

@@ -74,7 +74,7 @@ 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;
 	}

arch/mips/mm/mmap.c +1 -1

@@ -92,7 +92,7 @@ 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;
 	}

arch/parisc/kernel/sys_parisc.c +9 -6

@@ -88,7 +88,7 @@ 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;

@@ -115,9 +115,10 @@ 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;
 	}

@@ -141,7 +142,7 @@ 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;

@@ -175,9 +176,11 @@ 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;
 	}

arch/powerpc/mm/slice.c +1 -1

@@ -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)

arch/s390/mm/mmap.c +2 -2

@@ -97,7 +97,7 @@ 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;
 	}

@@ -135,7 +135,7 @@ 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;
 	}

arch/sh/mm/mmap.c +2 -2

@@ -63,7 +63,7 @@ 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;
 	}

@@ -113,7 +113,7 @@ 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;
 	}

arch/sparc/kernel/sys_sparc_64.c +2 -2

@@ -118,7 +118,7 @@ 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;
 	}

@@ -181,7 +181,7 @@ 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;
 	}

arch/sparc/mm/hugetlbpage.c +1 -1

@@ -115,7 +115,7 @@ hugetlb_get_unmapped_area(struct file *f
 		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)

arch/tile/mm/hugetlbpage.c +1 -1

@@ -232,7 +232,7 @@ 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)

arch/x86/kernel/sys_x86_64.c +2 -2

@@ -143,7 +143,7 @@ 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;
 	}

@@ -186,7 +186,7 @@ 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;
 	}

arch/x86/mm/hugetlbpage.c +1 -1

@@ -144,7 +144,7 @@ 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)

arch/xtensa/kernel/syscall.c +1 -1

@@ -87,7 +87,7 @@ 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)

fs/hugetlbfs/inode.c +1 -1

@@ -191,7 +191,7 @@ 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;
 	}

fs/proc/task_mmu.c +0 -4

@@ -295,11 +295,7 @@ 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 ",

include/linux/mm.h +25 ~~-30~~

78 lines not on this page · raw message

mm/gup.c +0 -5

@@ -312,11 +312,6 @@ 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 (nonblocking)

mm/memory.c +0 ~~-38~~

@@ -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_s
 	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),

mm/mmap.c +88 ~~-59~~

313 lines not on this page · raw message

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/mm-larger-stack-guard-gap-between-vmas.patch