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authorMark Rutland <mark.rutland@arm.com>2018-04-05 16:25:12 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-04-05 21:36:27 -0700
commit3eda69c92d4751977baf2d34e88a29d4b6affa7d (patch)
tree931b5551d4d8a4732375d10f2babac7d74628798
parent0c7c1bed7e13dbb545375c231e6ba1dca5e8d725 (diff)
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@arm.com Signed-off-by: Mark Rutland <mark.rutland@arm.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Will Deacon <will.deacon@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--kernel/fork.c2
-rw-r--r--kernel/sched/core.c1
2 files changed, 3 insertions, 0 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index f71b67dc156d..242c8c93d285 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -595,6 +595,8 @@ static void check_mm(struct mm_struct *mm)
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 --git a/kernel/sched/core.c b/kernel/sched/core.c
index 28b68995a417..e8afd6086f23 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5560,6 +5560,7 @@ 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);