| Message ID | 20180312140103.19235-1-mark.rutland@arm.com |
|---|---|
| State | New |
| Headers | show |
| Series | [PATCHv2] Detect early free of a live mm | expand |
diff --git a/kernel/fork.c b/kernel/fork.c index e5d9d405ae4e..ac94ce894219 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 e7c535eee0a6..0ef844abc2da 100644 --- a/kernel/sched/core.c +++ b/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);
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. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: 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> --- kernel/fork.c | 2 ++ kernel/sched/core.c | 1 + 2 files changed, 3 insertions(+) Since v1 [1]: * Use WARN_ON_ONCE() * Avoid spurious warning in idle_task_exit() Mark. [1] https://lkml.kernel.org/r/20180228121458.2230-1-mark.rutland@arm.com -- 2.11.0