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

fs/proc: Stop trying to report thread stacks

to the 3.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: fs-proc-stop-trying-to-report-thread-stacks.patch and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From b18cb64ead400c01bf1580eeba330ace51f8087d Mon Sep 17 00:00:00 2001

From: Andy Lutomirski luto@kernel.org Date: Fri, 30 Sep 2016 10:58:57 -0700 Subject: fs/proc: Stop trying to report thread stacks

From: Andy Lutomirski luto@kernel.org

commit b18cb64ead400c01bf1580eeba330ace51f8087d upstream.

This reverts more of:

b76437579d13 ("procfs: mark thread stack correctly in proc/<pid>/maps")

... which was partially reverted by:

65376df58217 ("proc: revert /proc/<pid>/maps [stack:TID] annotation")

Originally, /proc/PID/task/TID/maps was the same as /proc/TID/maps.

In current kernels, /proc/PID/maps (or /proc/TID/maps even for threads) shows "[stack]" for VMAs in the mm's stack address range.

In contrast, /proc/PID/task/TID/maps uses KSTK_ESP to guess the target thread's stack's VMA. This is racy, probably returns garbage and, on arches with CONFIG_TASK_INFO_IN_THREAD=y, is also crash-prone: KSTK_ESP is not safe to use on tasks that aren't known to be running ordinary process-context kernel code.

This patch removes the difference and just shows "[stack]" for VMAs in the mm's stack range. This is IMO much more sensible -- the actual "stack" address really is treated specially by the VM code, and the current thread stack isn't even well-defined for programs that frequently switch stacks on their own.

Reported-by: Jann Horn jann@thejh.net Signed-off-by: Andy Lutomirski luto@kernel.org Acked-by: Thomas Gleixner tglx@linutronix.de Cc: Al Viro viro@zeniv.linux.org.uk Cc: Andrew Morton akpm@linux-foundation.org Cc: Borislav Petkov bp@alien8.de Cc: Brian Gerst brgerst@gmail.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Kees Cook keescook@chromium.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Linux API linux-api@vger.kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Tycho Andersen tycho.andersen@canonical.com Link: http://lkml.kernel.org/r/3e678474ec14e0a0ec34c611016753eea2e1b8ba.1475257877... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- Documentation/filesystems/proc.txt | 26 -------------------------- fs/proc/task_mmu.c | 29 ++++++++++------------------- fs/proc/task_nommu.c | 26 +++++++++----------------- 3 files changed, 19 insertions(+), 62 deletions(-)

--- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -371,32 +371,6 @@ is not associated with a file:

or if empty, the mapping is anonymous.

-The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint -of the individual tasks of a process. In this file you will see a mapping marked -as [stack] if that task sees it as a stack. Hence, for the example above, the -task-level map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this: - -08048000-08049000 r-xp 00000000 03:00 8312 /opt/test -08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test -0804a000-0806b000 rw-p 00000000 00:00 0 [heap] -a7cb1000-a7cb2000 ---p 00000000 00:00 0 -a7cb2000-a7eb2000 rw-p 00000000 00:00 0 -a7eb2000-a7eb3000 ---p 00000000 00:00 0 -a7eb3000-a7ed5000 rw-p 00000000 00:00 0 [stack] -a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6 -a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6 -a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6 -a800b000-a800e000 rw-p 00000000 00:00 0 -a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0 -a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0 -a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0 -a8024000-a8027000 rw-p 00000000 00:00 0 -a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2 -a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2 -a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2 -aff35000-aff4a000 rw-p 00000000 00:00 0 -ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso] - The /proc/PID/smaps is an extension based on maps, showing the memory consumption for each of the process's mappings. For each of mappings there is a series of lines such as the following: --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -248,24 +248,15 @@ static int do_maps_open(struct inode *in * /proc/PID/maps that is the stack of the main task. */ static int is_stack(struct proc_maps_private *priv, - struct vm_area_struct *vma, int is_pid) + struct vm_area_struct *vma) { - int stack = 0; - - if (is_pid) { - stack = vma->vm_start <= vma->vm_mm->start_stack && - vma->vm_end >= vma->vm_mm->start_stack; - } else { - struct inode *inode = priv->inode; - struct task_struct *task; - - rcu_read_lock(); - task = pid_task(proc_pid(inode), PIDTYPE_PID); - if (task) - stack = vma_is_stack_for_task(vma, task); - rcu_read_unlock(); - } - return stack; + /* + * We make no effort to guess what a given thread considers to be + * its "stack". It's not even well-defined for programs written + * languages like Go. + */ + return vma->vm_start <= vma->vm_mm->start_stack && + vma->vm_end >= vma->vm_mm->start_stack; }

static void @@ -332,7 +323,7 @@ show_map_vma(struct seq_file *m, struct goto done; }

- if (is_stack(priv, vma, is_pid)) + if (is_stack(priv, vma)) name = "[stack]"; }

@@ -1501,7 +1492,7 @@ static int show_numa_map(struct seq_file seq_path(m, &file->f_path, "\n\t= "); } else if (vma->vm_start <= mm->brk && vma->vm_end >= mm->start_brk) { seq_puts(m, " heap"); - } else if (is_stack(proc_priv, vma, is_pid)) { + } else if (is_stack(proc_priv, vma)) { seq_puts(m, " stack"); }

--- a/fs/proc/task_nommu.c +++ b/fs/proc/task_nommu.c @@ -124,25 +124,17 @@ unsigned long task_statm(struct mm_struc }

static int is_stack(struct proc_maps_private *priv, - struct vm_area_struct *vma, int is_pid) + struct vm_area_struct *vma) { struct mm_struct *mm = vma->vm_mm; - int stack = 0;

- if (is_pid) { - stack = vma->vm_start <= mm->start_stack && - vma->vm_end >= mm->start_stack; - } else { - struct inode *inode = priv->inode; - struct task_struct *task; - - rcu_read_lock(); - task = pid_task(proc_pid(inode), PIDTYPE_PID); - if (task) - stack = vma_is_stack_for_task(vma, task); - rcu_read_unlock(); - } - return stack; + /* + * We make no effort to guess what a given thread considers to be + * its "stack". It's not even well-defined for programs written + * languages like Go. + */ + return vma->vm_start <= mm->start_stack && + vma->vm_end >= mm->start_stack; }

/* @@ -184,7 +176,7 @@ static int nommu_vma_show(struct seq_fil if (file) { seq_pad(m, ' '); seq_path(m, &file->f_path, ""); - } else if (mm && is_stack(priv, vma, is_pid)) { + } else if (mm && is_stack(priv, vma)) { seq_pad(m, ' '); seq_printf(m, "[stack]"); }

Patches currently in stable-queue which might be from luto@kernel.org are

queue-3.18/perf-hwbp-simplify-the-perf-hwbp-code-fix-documentation.patch queue-3.18/fs-proc-stop-trying-to-report-thread-stacks.patch queue-3.18/kvm-x86-fix-icebp-instruction-handling.patch