Re: [RFC PATCH v3] UML: add support for KASAN under x86_64

[Dmitry Vyukov <dvyukov@google.com>]

On Fri, 27 May 2022 at 16:28, Johannes Berg <johannes@sipsolutions.net> wrote:
> > > > > On Fri, 2022-05-27 at 15:09 +0200, Dmitry Vyukov wrote:
> > > > > > > I did note (this is more for kasan-dev@) that the "freed by" is fairly
> > > > > > > much useless when using kfree_rcu(), it might be worthwhile to annotate
> > > > > > > that somehow, so the stack trace is recorded by kfree_rcu() already,
> > > > > > > rather than just showing the RCU callback used for that.
> [...]
> > Humm... I don't have any explanation based only on this info.
> > Generally call_rcu stacks are memorized and I see the call is still there:
> > https://elixir.bootlin.com/linux/v5.18/source/kernel/rcu/tree.c#L3595
>
> Oh, that's simple then, UML is !SMP && !PREEMPT so it gets TINY_RCU
> instead of TREE_RCU.

Nice!

> Unfortunately, it's not entirely trivial to fix, something like this,
> mostly because of header maze (cannot include kasan.h in rcutiny.h):
>
> diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> index 5fed476f977f..d84e13f2c384 100644
> --- a/include/linux/rcutiny.h
> +++ b/include/linux/rcutiny.h
> @@ -38,7 +38,7 @@ static inline void synchronize_rcu_expedited(void)
>   */
>  extern void kvfree(const void *addr);
>
> -static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> +static inline void __kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
>  {
>         if (head) {
>                 call_rcu(head, func);
> @@ -51,6 +51,15 @@ static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
>         kvfree((void *) func);
>  }
>
> +#ifdef CONFIG_KASAN_GENERIC
> +void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func);
> +#else
> +static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> +{
> +       __kvfree_call_rcu(head, func);
> +}
> +#endif
> +
>  void rcu_qs(void);
>
>  static inline void rcu_softirq_qs(void)
> diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
> index 340b3f8b090d..aa235f0332ba 100644
> --- a/kernel/rcu/tiny.c
> +++ b/kernel/rcu/tiny.c
> @@ -217,6 +217,18 @@ bool poll_state_synchronize_rcu(unsigned long oldstate)
>  }
>  EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
>
> +void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> +{
> +       if (head) {
> +               void *ptr = (void *) head - (unsigned long) func;
> +
> +               kasan_record_aux_stack_noalloc(ptr);
> +       }
> +
> +       __kvfree_call_rcu(head, func);
> +}
> +EXPORT_SYMBOL_GPL(kvfree_call_rcu);
> +
>  void __init rcu_init(void)
>  {
>         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
>
>
>
>
> Or I guess I could copy/paste
>
> #ifdef CONFIG_KASAN_GENERIC
> void kasan_record_aux_stack_noalloc(void *ptr);
> #else /* CONFIG_KASAN_GENERIC */
> static inline void kasan_record_aux_stack_noalloc(void *ptr) {}
> #endif /* CONFIG_KASAN_GENERIC */
>
>
> into rcutiny.h, that'd be smaller, and export the symbol ...
>
> johannes
>
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