fs/proc: Stop trying to report thread stacks
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.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index faacb0c..3717562 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -124,25 +124,17 @@ unsigned long task_statm(struct mm_struct *mm,
}
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_file *m, struct vm_area_struct *vma,
if (file) {
seq_pad(m, ' ');
seq_file_path(m, file, "");
- } else if (mm && is_stack(priv, vma, is_pid)) {
+ } else if (mm && is_stack(priv, vma)) {
seq_pad(m, ' ');
seq_printf(m, "[stack]");
}
