[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@xxxxxxxxx> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html