From 3eda69c92d4751977baf2d34e88a29d4b6affa7d Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Thu, 5 Apr 2018 16:25:12 -0700 Subject: [PATCH] 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 Reviewed-by: Andrew Morton Cc: Ingo Molnar Cc: Mathieu Desnoyers Cc: Michal Hocko Cc: Peter Zijlstra Cc: Rik van Riel Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/fork.c | 2 ++ kernel/sched/core.c | 1 + 2 files changed, 3 insertions(+) diff --git a/kernel/fork.c b/kernel/fork.c index f71b67d..242c8c9 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 28b6899..e8afd60 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); -- 2.7.4