Message-Id: <20241016090747.6a675265244880ace7d41718@kernel.org>
Date: Wed, 16 Oct 2024 09:07:47 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
 <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
 bpf@...r.kernel.org, Martin KaFai Lau <kafai@...com>, Song Liu
 <songliubraving@...com>, Yonghong Song <yhs@...com>, John Fastabend
 <john.fastabend@...il.com>, KP Singh <kpsingh@...omium.org>, Stanislav
 Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Steven Rostedt
 <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCHv6 perf/core 02/16] uprobe: Add support for session
 consumer

On Thu, 10 Oct 2024 22:09:43 +0200
Jiri Olsa <jolsa@...nel.org> wrote:

> This change allows the uprobe consumer to behave as session which
> means that 'handler' and 'ret_handler' callbacks are connected in
> a way that allows to:
> 
>   - control execution of 'ret_handler' from 'handler' callback
>   - share data between 'handler' and 'ret_handler' callbacks
> 
> The session concept fits to our common use case where we do filtering
> on entry uprobe and based on the result we decide to run the return
> uprobe (or not).
> 
> It's also convenient to share the data between session callbacks.
> 
> To achive this we are adding new return value the uprobe consumer
> can return from 'handler' callback:
> 
>   UPROBE_HANDLER_IGNORE
>   - Ignore 'ret_handler' callback for this consumer.

This is interesting idea. This means we can cancel exit handler
dynamically.

> 
> And store cookie and pass it to 'ret_handler' when consumer has both
> 'handler' and 'ret_handler' callbacks defined.
> 
> We store shared data in the return_consumer object array as part of
> the return_instance object. This way the handle_uretprobe_chain can
> find related return_consumer and its shared data.
> 
> We also store entry handler return value, for cases when there are
> multiple consumers on single uprobe and some of them are ignored and
> some of them not, in which case the return probe gets installed and
> we need to have a way to find out which consumer needs to be ignored.
> 
> The tricky part is when consumer is registered 'after' the uprobe
> entry handler is hit. In such case this consumer's 'ret_handler' gets
> executed as well, but it won't have the proper data pointer set,
> so we can filter it out.

Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thank you,

> Acked-by: Andrii Nakryiko <andrii@...nel.org>
> Suggested-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  include/linux/uprobes.h |  21 +++++-
>  kernel/events/uprobes.c | 148 ++++++++++++++++++++++++++++++++--------
>  2 files changed, 139 insertions(+), 30 deletions(-)
> 
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index bb265a632b91..dbaf04189548 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -23,8 +23,17 @@ struct inode;
>  struct notifier_block;
>  struct page;
>  
> +/*
> + * Allowed return values from uprobe consumer's handler callback
> + * with following meaning:
> + *
> + * UPROBE_HANDLER_REMOVE
> + * - Remove the uprobe breakpoint from current->mm.
> + * UPROBE_HANDLER_IGNORE
> + * - Ignore ret_handler callback for this consumer.
> + */
>  #define UPROBE_HANDLER_REMOVE		1
> -#define UPROBE_HANDLER_MASK		1
> +#define UPROBE_HANDLER_IGNORE		2
>  
>  #define MAX_URETPROBE_DEPTH		64
>  
> @@ -44,6 +53,8 @@ struct uprobe_consumer {
>  	bool (*filter)(struct uprobe_consumer *self, struct mm_struct *mm);
>  
>  	struct list_head cons_node;
> +
> +	__u64 id;	/* set when uprobe_consumer is registered */
>  };
>  
>  #ifdef CONFIG_UPROBES
> @@ -83,14 +94,22 @@ struct uprobe_task {
>  	unsigned int			depth;
>  };
>  
> +struct return_consumer {
> +	__u64	cookie;
> +	__u64	id;
> +};
> +
>  struct return_instance {
>  	struct uprobe		*uprobe;
>  	unsigned long		func;
>  	unsigned long		stack;		/* stack pointer */
>  	unsigned long		orig_ret_vaddr; /* original return address */
>  	bool			chained;	/* true, if instance is nested */
> +	int			consumers_cnt;
>  
>  	struct return_instance	*next;		/* keep as stack */
> +
> +	struct return_consumer	consumers[] __counted_by(consumers_cnt);
>  };
>  
>  enum rp_check {
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 6b44c386a5df..4ef4b51776eb 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -64,7 +64,7 @@ struct uprobe {
>  	struct rcu_head		rcu;
>  	loff_t			offset;
>  	loff_t			ref_ctr_offset;
> -	unsigned long		flags;
> +	unsigned long		flags;		/* "unsigned long" so bitops work */
>  
>  	/*
>  	 * The generic code assumes that it has two members of unknown type
> @@ -823,8 +823,11 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset,
>  
>  static void consumer_add(struct uprobe *uprobe, struct uprobe_consumer *uc)
>  {
> +	static atomic64_t id;
> +
>  	down_write(&uprobe->consumer_rwsem);
>  	list_add_rcu(&uc->cons_node, &uprobe->consumers);
> +	uc->id = (__u64) atomic64_inc_return(&id);
>  	up_write(&uprobe->consumer_rwsem);
>  }
>  
> @@ -1761,6 +1764,34 @@ static struct uprobe_task *get_utask(void)
>  	return current->utask;
>  }
>  
> +static size_t ri_size(int consumers_cnt)
> +{
> +	struct return_instance *ri;
> +
> +	return sizeof(*ri) + sizeof(ri->consumers[0]) * consumers_cnt;
> +}
> +
> +#define DEF_CNT 4
> +
> +static struct return_instance *alloc_return_instance(void)
> +{
> +	struct return_instance *ri;
> +
> +	ri = kzalloc(ri_size(DEF_CNT), GFP_KERNEL);
> +	if (!ri)
> +		return ZERO_SIZE_PTR;
> +
> +	ri->consumers_cnt = DEF_CNT;
> +	return ri;
> +}
> +
> +static struct return_instance *dup_return_instance(struct return_instance *old)
> +{
> +	size_t size = ri_size(old->consumers_cnt);
> +
> +	return kmemdup(old, size, GFP_KERNEL);
> +}
> +
>  static int dup_utask(struct task_struct *t, struct uprobe_task *o_utask)
>  {
>  	struct uprobe_task *n_utask;
> @@ -1773,11 +1804,10 @@ static int dup_utask(struct task_struct *t, struct uprobe_task *o_utask)
>  
>  	p = &n_utask->return_instances;
>  	for (o = o_utask->return_instances; o; o = o->next) {
> -		n = kmalloc(sizeof(struct return_instance), GFP_KERNEL);
> +		n = dup_return_instance(o);
>  		if (!n)
>  			return -ENOMEM;
>  
> -		*n = *o;
>  		/*
>  		 * uprobe's refcnt has to be positive at this point, kept by
>  		 * utask->return_instances items; return_instances can't be
> @@ -1870,35 +1900,31 @@ static void cleanup_return_instances(struct uprobe_task *utask, bool chained,
>  	utask->return_instances = ri;
>  }
>  
> -static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
> +static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs,
> +			      struct return_instance *ri)
>  {
>  	struct uprobe_task *utask = current->utask;
>  	unsigned long orig_ret_vaddr, trampoline_vaddr;
> -	struct return_instance *ri;
>  	bool chained;
>  
>  	if (!get_xol_area())
> -		return;
> +		goto free;
>  
>  	if (utask->depth >= MAX_URETPROBE_DEPTH) {
>  		printk_ratelimited(KERN_INFO "uprobe: omit uretprobe due to"
>  				" nestedness limit pid/tgid=%d/%d\n",
>  				current->pid, current->tgid);
> -		return;
> +		goto free;
>  	}
>  
>  	/* we need to bump refcount to store uprobe in utask */
>  	if (!try_get_uprobe(uprobe))
> -		return;
> -
> -	ri = kmalloc(sizeof(struct return_instance), GFP_KERNEL);
> -	if (!ri)
> -		goto fail;
> +		goto free;
>  
>  	trampoline_vaddr = uprobe_get_trampoline_vaddr();
>  	orig_ret_vaddr = arch_uretprobe_hijack_return_addr(trampoline_vaddr, regs);
>  	if (orig_ret_vaddr == -1)
> -		goto fail;
> +		goto put;
>  
>  	/* drop the entries invalidated by longjmp() */
>  	chained = (orig_ret_vaddr == trampoline_vaddr);
> @@ -1916,7 +1942,7 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
>  			 * attack from user-space.
>  			 */
>  			uprobe_warn(current, "handle tail call");
> -			goto fail;
> +			goto put;
>  		}
>  		orig_ret_vaddr = utask->return_instances->orig_ret_vaddr;
>  	}
> @@ -1931,9 +1957,10 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
>  	utask->return_instances = ri;
>  
>  	return;
> -fail:
> -	kfree(ri);
> +put:
>  	put_uprobe(uprobe);
> +free:
> +	kfree(ri);
>  }
>  
>  /* Prepare to single-step probed instruction out of line. */
> @@ -2077,34 +2104,90 @@ static struct uprobe *find_active_uprobe_rcu(unsigned long bp_vaddr, int *is_swb
>  	return uprobe;
>  }
>  
> +static struct return_instance*
> +push_consumer(struct return_instance *ri, int idx, __u64 id, __u64 cookie)
> +{
> +	if (unlikely(ri == ZERO_SIZE_PTR))
> +		return ri;
> +
> +	if (unlikely(idx >= ri->consumers_cnt)) {
> +		struct return_instance *old_ri = ri;
> +
> +		ri->consumers_cnt += DEF_CNT;
> +		ri = krealloc(old_ri, ri_size(old_ri->consumers_cnt), GFP_KERNEL);
> +		if (!ri) {
> +			kfree(old_ri);
> +			return ZERO_SIZE_PTR;
> +		}
> +	}
> +
> +	ri->consumers[idx].id = id;
> +	ri->consumers[idx].cookie = cookie;
> +	return ri;
> +}
> +
> +static struct return_consumer *
> +return_consumer_find(struct return_instance *ri, int *iter, int id)
> +{
> +	struct return_consumer *ric;
> +	int idx = *iter;
> +
> +	for (ric = &ri->consumers[idx]; idx < ri->consumers_cnt; idx++, ric++) {
> +		if (ric->id == id) {
> +			*iter = idx + 1;
> +			return ric;
> +		}
> +	}
> +	return NULL;
> +}
> +
> +static bool ignore_ret_handler(int rc)
> +{
> +	return rc == UPROBE_HANDLER_REMOVE || rc == UPROBE_HANDLER_IGNORE;
> +}
> +
>  static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
>  {
>  	struct uprobe_consumer *uc;
> -	int remove = UPROBE_HANDLER_REMOVE;
> -	bool need_prep = false; /* prepare return uprobe, when needed */
> -	bool has_consumers = false;
> +	bool has_consumers = false, remove = true;
> +	struct return_instance *ri = NULL;
> +	int push_idx = 0;
>  
>  	current->utask->auprobe = &uprobe->arch;
>  
>  	list_for_each_entry_rcu(uc, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
> +		bool session = uc->handler && uc->ret_handler;
> +		__u64 cookie = 0;
>  		int rc = 0;
>  
>  		if (uc->handler) {
> -			rc = uc->handler(uc, regs, NULL);
> -			WARN(rc & ~UPROBE_HANDLER_MASK,
> +			rc = uc->handler(uc, regs, &cookie);
> +			WARN(rc < 0 || rc > 2,
>  				"bad rc=0x%x from %ps()\n", rc, uc->handler);
>  		}
>  
> -		if (uc->ret_handler)
> -			need_prep = true;
> -
> -		remove &= rc;
> +		remove &= rc == UPROBE_HANDLER_REMOVE;
>  		has_consumers = true;
> +
> +		if (!uc->ret_handler || ignore_ret_handler(rc))
> +			continue;
> +
> +		if (!ri)
> +			ri = alloc_return_instance();
> +
> +		if (session)
> +			ri = push_consumer(ri, push_idx++, uc->id, cookie);
>  	}
>  	current->utask->auprobe = NULL;
>  
> -	if (need_prep && !remove)
> -		prepare_uretprobe(uprobe, regs); /* put bp at return */
> +	if (!ZERO_OR_NULL_PTR(ri)) {
> +		/*
> +		 * The push_idx value has the final number of return consumers,
> +		 * and ri->consumers_cnt has number of allocated consumers.
> +		 */
> +		ri->consumers_cnt = push_idx;
> +		prepare_uretprobe(uprobe, regs, ri);
> +	}
>  
>  	if (remove && has_consumers) {
>  		down_read(&uprobe->register_rwsem);
> @@ -2123,12 +2206,19 @@ static void
>  handle_uretprobe_chain(struct return_instance *ri, struct pt_regs *regs)
>  {
>  	struct uprobe *uprobe = ri->uprobe;
> +	struct return_consumer *ric;
>  	struct uprobe_consumer *uc;
> +	int ric_idx = 0;
>  
>  	rcu_read_lock_trace();
>  	list_for_each_entry_rcu(uc, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
> -		if (uc->ret_handler)
> -			uc->ret_handler(uc, ri->func, regs, NULL);
> +		bool session = uc->handler && uc->ret_handler;
> +
> +		if (uc->ret_handler) {
> +			ric = return_consumer_find(ri, &ric_idx, uc->id);
> +			if (!session || ric)
> +				uc->ret_handler(uc, ri->func, regs, ric ? &ric->cookie : NULL);
> +		}
>  	}
>  	rcu_read_unlock_trace();
>  }
> -- 
> 2.46.2
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>

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