The patch titled
Subject: kernel/fork.c: detect early free of a live mm
has been added to the -mm tree. Its filename is
detect-early-free-of-a-live-mm.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/detect-early-free-of-a-live-mm.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/detect-early-free-of-a-live-mm.patch
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------------------------------------------------------
From: Mark Rutland <mark.rutland@xxxxxxx>
Subject: kernel/fork.c: detect early free of a live mm
KASAN splats indicate that in some cases we free a live mm, then continue
to access it, with potentially disastrous results. This is likely due to
a mismatched mmdrop() somewhere in the kernel, but so far the culprit
remains elusive.
Let's have __mmdrop() verify that the mm isn't live for the current task,
similar to the existing check for init_mm. This way, we can catch this
class of issue earlier, and without requiring KASAN.
Currently, idle_task_exit() leaves active_mm stale after it switches to
init_mm. This isn't harmful, but will trigger the new assertions, so we
must adjust idle_task_exit() to update active_mm.
Link: http://lkml.kernel.org/r/20180312140103.19235-1-mark.rutland@xxxxxxx
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/fork.c | 2 ++
kernel/sched/core.c | 1 +
2 files changed, 3 insertions(+)
diff -puN kernel/fork.c~detect-early-free-of-a-live-mm kernel/fork.c
--- a/kernel/fork.c~detect-early-free-of-a-live-mm
+++ a/kernel/fork.c
@@ -595,6 +595,8 @@ static void check_mm(struct mm_struct *m
void __mmdrop(struct mm_struct *mm)
{
BUG_ON(mm == &init_mm);
+ WARN_ON_ONCE(mm == current->mm);
+ WARN_ON_ONCE(mm == current->active_mm);
mm_free_pgd(mm);
destroy_context(mm);
hmm_mm_destroy(mm);
diff -puN kernel/sched/core.c~detect-early-free-of-a-live-mm kernel/sched/core.c
--- a/kernel/sched/core.c~detect-early-free-of-a-live-mm
+++ a/kernel/sched/core.c
@@ -5506,6 +5506,7 @@ void idle_task_exit(void)
if (mm != &init_mm) {
switch_mm(mm, &init_mm, current);
+ current->active_mm = &init_mm;
finish_arch_post_lock_switch();
}
mmdrop(mm);
_
Patches currently in -mm which might be from mark.rutland@xxxxxxx are
detect-early-free-of-a-live-mm.patch
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