Re: [PATCH rcu 07/12] rcu: tiny: Record kvfree_call_rcu() call stack for KASAN

Neeraj Upadhyay
2022-06-21T06:31:38Z

On 6/21/2022 3:50 AM, Paul E. McKenney wrote:
> From: Johannes Berg <johannes.berg@intel.com>
>
> When running KASAN with Tiny RCU (e.g. under ARCH=um, where
> a working KASAN patch is now available), we don't get any
> information on the original kfree_rcu() (or similar) caller
> when a problem is reported, as Tiny RCU doesn't record this.
>
> Add the recording, which required pulling kvfree_call_rcu()
> out of line for the KASAN case since the recording function
> (kasan_record_aux_stack_noalloc) is neither exported, nor
> can we include kasan.h into rcutiny.h.
>
> without KASAN, the patch has no size impact (ARCH=um kernel):
> text data bss dec hex filename
> 6151515 4423154 33148520 43723189 29b29b5 linux
> 6151515 4423154 33148520 43723189 29b29b5 linux + patch
>
> with KASAN, the impact on my build was minimal:
> text data bss dec hex filename
> 13915539 7388050 33282304 54585893 340ea25 linux
> 13911266 7392114 33282304 54585684 340e954 linux + patch
> -4273 +4064 +-0 -209
>
> Acked-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> ---
> include/linux/rcutiny.h | 11 ++++++++++-
> kernel/rcu/tiny.c | 14 ++++++++++++++
> 2 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> index 5fed476f977f6..d84e13f2c3848 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 340b3f8b090d4..58ff3721d975c 100644
> --- a/kernel/rcu/tiny.c
> +++ b/kernel/rcu/tiny.c
> @@ -217,6 +217,20 @@ bool poll_state_synchronize_rcu(unsigned long oldstate)
> }
> EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
>
> +#ifdef CONFIG_KASAN_GENERIC
> +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);
> + }

For the !head case; similar to Tree RCU's kvfree_call_rcu()
implementation, we do not need to record 'ptr' (which will be 'func')?

Thanks
Neeraj

> +
> + __kvfree_call_rcu(head, func);
> +}
> +EXPORT_SYMBOL_GPL(kvfree_call_rcu);
> +#endif
> +
> void __init rcu_init(void)
> {
> open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);