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Subject: [RESEND][PATCH] Mark thread stack correctly in proc/<pid>/maps
From: Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com>
To: Jamie Lokier <jamie@shareable.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org,
        Michael Kerrisk <mtk.manpages@gmail.com>, linux-man@vger.kernel.org,
        Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com>
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Hi,

Resending since I did not get any feedback on the second take of the patch.

Thanks,
Siddhesh


---------- Forwarded message ----------
From: Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com>
Date: Tue, Jan 17, 2012 at 10:24 AM
Subject: [PATCH] Mark thread stack correctly in proc/<pid>/maps
To: Jamie Lokier <jamie@shareable.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alexander Viro
<viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org, Michael
Kerrisk <mtk.manpages@gmail.com>, linux-man@vger.kernel.org, Siddhesh
Poyarekar <siddhesh.poyarekar@gmail.com>


[Take 2]

Memory mmaped by glibc for a thread stack currently shows up as a simple
anonymous map, which makes it difficult to differentiate between memory
usage of the thread on stack and other dynamic allocation. Since glibc
already uses MAP_STACK to request this mapping, the attached patch
uses this flag to add additional VM_STACK_FLAGS to the resulting vma
so that the mapping is treated as a stack and not any regular
anonymous mapping. Also, one may use vm_flags to decide if a vma is a
stack.

This patch also changes the maps output to annotate stack guards for
both the process stack as well as the thread stacks. Thus is born the
[stack guard] annotation, which should be exactly a page long for the
process stack and can be longer than a page (configurable in
userspace) for POSIX compliant thread stacks. A thread stack guard is
simply page(s) with PROT_NONE.

If accepted, this should also reflect in the man page for mmap since
MAP_STACK will no longer be a noop.

Signed-off-by: Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com>
---
?fs/proc/task_mmu.c | ? 41 ++++++++++++++++++++++++++++++++++++-----
?include/linux/mm.h | ? 19 +++++++++++++++++--
?mm/mmap.c ? ? ? ? ?| ? ?3 +++
?3 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index e418c5a..650330c 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -227,13 +227,42 @@ static void show_map_vma(struct seq_file *m,
struct vm_area_struct *vma)
? ? ? ? ? ? ? ?pgoff = ((loff_t)vma->vm_pgoff) << PAGE_SHIFT;
? ? ? ?}

- ? ? ? /* We don't show the stack guard page in /proc/maps */
+ ? ? ? /*
+ ? ? ? ?* Mark the process stack guard, which is just one page at the
+ ? ? ? ?* beginning of the stack within the stack vma.
+ ? ? ? ?*/
? ? ? ?start = vma->vm_start;
- ? ? ? if (stack_guard_page_start(vma, start))
+ ? ? ? if (stack_guard_page_start(vma, start)) {
+ ? ? ? ? ? ? ? seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? start,
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? start + PAGE_SIZE,
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? flags & VM_READ ? 'r' : '-',
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? flags & VM_WRITE ? 'w' : '-',
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? flags & VM_EXEC ? 'x' : '-',
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? flags & VM_MAYSHARE ? 's' : 'p',
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? pgoff,
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? MAJOR(dev), MINOR(dev), ino, &len);
+
+ ? ? ? ? ? ? ? pad_len_spaces(m, len);
+ ? ? ? ? ? ? ? seq_puts(m, "[stack guard]\n");
? ? ? ? ? ? ? ?start += PAGE_SIZE;
+ ? ? ? }
? ? ? ?end = vma->vm_end;
- ? ? ? if (stack_guard_page_end(vma, end))
+ ? ? ? if (stack_guard_page_end(vma, end)) {
+ ? ? ? ? ? ? ? seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? end - PAGE_SIZE,
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? end,
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? flags & VM_READ ? 'r' : '-',
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? flags & VM_WRITE ? 'w' : '-',
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? flags & VM_EXEC ? 'x' : '-',
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? flags & VM_MAYSHARE ? 's' : 'p',
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? pgoff,
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? MAJOR(dev), MINOR(dev), ino, &len);
+
+ ? ? ? ? ? ? ? pad_len_spaces(m, len);
+ ? ? ? ? ? ? ? seq_puts(m, "[stack guard]\n");
? ? ? ? ? ? ? ?end -= PAGE_SIZE;
+ ? ? ? }

? ? ? ?seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
? ? ? ? ? ? ? ? ? ? ? ?start,
@@ -259,8 +288,10 @@ static void show_map_vma(struct seq_file *m,
struct vm_area_struct *vma)
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?if (vma->vm_start <= mm->brk &&
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?vma->vm_end >= mm->start_brk) {
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?name = "[heap]";
- ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? } else if (vma->vm_start <= mm->start_stack &&
- ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?vma->vm_end >= mm->start_stack) {
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? } else if (vma_is_stack(vma) &&
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?vma_is_guard(vma)) {
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? name = "[stack guard]";
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? } else if (vma_is_stack(vma)) {
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?name = "[stack]";
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?}
? ? ? ? ? ? ? ? ? ? ? ?} else {
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 17b27cd..4e57753 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1018,12 +1018,26 @@ 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 int vma_is_stack(struct vm_area_struct *vma)
+{
+ ? ? ? return vma && (vma->vm_flags & (VM_GROWSUP | VM_GROWSDOWN));
+}
+
+/*
+ * Check guard set by userspace (PROT_NONE)
+ */
+static inline int vma_is_guard(struct vm_area_struct *vma)
+{
+ ? ? ? return (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC |
VM_SHARED)) == 0;
+}
+
?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);
+ ? ? ? ? ? ? ? !vma_growsdown(vma->vm_prev, addr) &&
+ ? ? ? ? ? ? ? !vma_is_guard(vma);
?}

?/* Is the vma a continuation of the stack vma below it? */
@@ -1037,7 +1051,8 @@ static inline int stack_guard_page_end(struct
vm_area_struct *vma,
?{
? ? ? ?return (vma->vm_flags & VM_GROWSUP) &&
? ? ? ? ? ? ? ?(vma->vm_end == addr) &&
- ? ? ? ? ? ? ? !vma_growsup(vma->vm_next, addr);
+ ? ? ? ? ? ? ? !vma_growsup(vma->vm_next, addr) &&
+ ? ? ? ? ? ? ? !vma_is_guard(vma);
?}

?extern unsigned long move_page_tables(struct vm_area_struct *vma,
diff --git a/mm/mmap.c b/mm/mmap.c
index 3f758c7..2f9f540 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -992,6 +992,9 @@ unsigned long do_mmap_pgoff(struct file *file,
unsigned long addr,
? ? ? ?vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags) |
? ? ? ? ? ? ? ? ? ? ? ?mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;

+ ? ? ? if (flags & MAP_STACK)
+ ? ? ? ? ? ? ? vm_flags |= VM_STACK_FLAGS;
+
? ? ? ?if (flags & MAP_LOCKED)
? ? ? ? ? ? ? ?if (!can_do_mlock())
? ? ? ? ? ? ? ? ? ? ? ?return -EPERM;
--
1.7.7.4



-- 
Siddhesh Poyarekar
http://siddhesh.in
--
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