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 @@ -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); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
