Re: [PATCHv3 1/7] uprobe: Add support for session consumer

Masami Hiramatsu
2024-09-10T14:10:29Z

On Mon, 9 Sep 2024 09:45:48 +0200
Jiri Olsa <jolsa@kernel.org> wrote:

> Adding support for uprobe consumer to be defined as session and have
> new behaviour for consumer's 'handler' and 'ret_handler' callbacks.
>
> The session 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 is enabled by setting new 'session' bool field to true
> in uprobe_consumer object.
>
> We use return_consumer object to keep track of consumers with
> 'ret_handler'. This object also carries the shared data between
> 'handler' and and 'ret_handler' callbacks.
>
> The control of 'ret_handler' callback execution is done via return
> value of the 'handler' callback. This patch adds new 'ret_handler'
> return value (2) which means to ignore ret_handler callback.
>
> Actions on 'handler' callback return values are now:
>
> 0 - execute ret_handler (if it's defined)
> 1 - remove uprobe
> 2 - do nothing (ignore ret_handler)
>
> 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).

OK, so this allows uprobes handler to record any input parameter and
access it from ret_handler as fprobe's private entry data, right?

The code looks good to me.

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

trace_uprobe should also support $argN in retuprobe.

https://lore.kernel.org/all/170952365552.229804.224112990211602895.stgit@devnote2/

Thank you,

>
> It's also convenient to share the data between session callbacks.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> include/linux/uprobes.h | 17 ++-
> kernel/events/uprobes.c | 132 ++++++++++++++----
> kernel/trace/bpf_trace.c | 6 +-
> kernel/trace/trace_uprobe.c | 12 +-
> .../selftests/bpf/bpf_testmod/bpf_testmod.c | 2 +-
> 5 files changed, 133 insertions(+), 36 deletions(-)
>
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 2b294bf1881f..557901e04624 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -24,7 +24,7 @@ struct notifier_block;
> struct page;
>
> #define UPROBE_HANDLER_REMOVE 1
> -#define UPROBE_HANDLER_MASK 1
> +#define UPROBE_HANDLER_IGNORE 2
>
> #define MAX_URETPROBE_DEPTH 64
>
> @@ -37,13 +37,16 @@ struct uprobe_consumer {
> * for the current process. If filter() is omitted or returns true,
> * UPROBE_HANDLER_REMOVE is effectively ignored.
> */
> - int (*handler)(struct uprobe_consumer *self, struct pt_regs *regs);
> + int (*handler)(struct uprobe_consumer *self, struct pt_regs *regs, __u64 *data);
> int (*ret_handler)(struct uprobe_consumer *self,
> unsigned long func,
> - struct pt_regs *regs);
> + struct pt_regs *regs, __u64 *data);
> bool (*filter)(struct uprobe_consumer *self, struct mm_struct *mm);
>
> struct list_head cons_node;
> + bool session;
> +
> + __u64 id; /* set when uprobe_consumer is registered */
> };
>
> #ifdef CONFIG_UPROBES
> @@ -83,14 +86,22 @@ 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 4b7e590dc428..9e971f86afdf 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -67,6 +67,8 @@ struct uprobe {
> loff_t ref_ctr_offset;
> unsigned long flags;
>
> + unsigned int consumers_cnt;
> +
> /*
> * The generic code assumes that it has two members of unknown type
> * owned by the arch-specific code:
> @@ -826,8 +828,12 @@ 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);
> + uprobe->consumers_cnt++;
> up_write(&uprobe->consumer_rwsem);
> }
>
> @@ -839,6 +845,7 @@ static void consumer_del(struct uprobe *uprobe, struct uprobe_consumer *uc)
> {
> down_write(&uprobe->consumer_rwsem);
> list_del_rcu(&uc->cons_node);
> + uprobe->consumers_cnt--;
> up_write(&uprobe->consumer_rwsem);
> }
>
> @@ -1786,6 +1793,30 @@ 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;
> +}
> +
> +static struct return_instance *alloc_return_instance(int consumers_cnt)
> +{
> + struct return_instance *ri;
> +
> + ri = kzalloc(ri_size(consumers_cnt), GFP_KERNEL);
> + if (ri)
> + ri->consumers_cnt = consumers_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;
> @@ -1798,11 +1829,10 @@ 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
> @@ -1895,39 +1925,35 @@ 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 return_instance *ri;
> struct uprobe_task *utask;
> unsigned long orig_ret_vaddr, trampoline_vaddr;
> bool chained;
>
> if (!get_xol_area())
> - return;
> + goto free;
>
> utask = get_utask();
> if (!utask)
> - 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);
> @@ -1945,7 +1971,7 @@ 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;
> }
> @@ -1960,9 +1986,10 @@ 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. */
> @@ -2114,35 +2141,78 @@ static struct uprobe *find_active_uprobe_rcu(unsigned long bp_vaddr, int *is_swb
> return uprobe;
> }
>
> +static struct return_consumer *
> +return_consumer_next(struct return_instance *ri, struct return_consumer *ric)
> +{
> + return ric ? ric + 1 : &ri->consumers[0];
> +}
> +
> +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 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 */
> + struct return_consumer *ric = NULL;
> + struct return_instance *ri = NULL;
> bool has_consumers = false;
>
> current->utask->auprobe = &uprobe->arch;
>
> list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node,
> srcu_read_lock_held(&uprobes_srcu)) {
> + __u64 cookie = 0;
> int rc = 0;
>
> if (uc->handler) {
> - rc = uc->handler(uc, regs);
> - 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;
> -
> + /*
> + * The handler can return following values:
> + * 0 - execute ret_handler (if it's defined)
> + * 1 - remove uprobe
> + * 2 - do nothing (ignore ret_handler)
> + */
> remove &= rc;
> has_consumers = true;
> +
> + if (rc == 0 && uc->ret_handler) {
> + /*
> + * Preallocate return_instance object optimistically with
> + * all possible consumers, so we allocate just once.
> + */
> + if (!ri) {
> + ri = alloc_return_instance(uprobe->consumers_cnt);
> + if (!ri)
> + return;
> + }
> + ric = return_consumer_next(ri, ric);
> + ric->cookie = cookie;
> + ric->id = uc->id;
> + }
> }
> current->utask->auprobe = NULL;
>
> - if (need_prep && !remove)
> - prepare_uretprobe(uprobe, regs); /* put bp at return */
> + if (ri && !remove)
> + prepare_uretprobe(uprobe, regs, ri); /* put bp at return */
> + else
> + kfree(ri);
>
> if (remove && has_consumers) {
> down_read(&uprobe->register_rwsem);
> @@ -2160,15 +2230,25 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
> static void
> handle_uretprobe_chain(struct return_instance *ri, struct pt_regs *regs)
> {
> + struct return_consumer *ric = NULL;
> struct uprobe *uprobe = ri->uprobe;
> struct uprobe_consumer *uc;
> - int srcu_idx;
> + int srcu_idx, iter = 0;
>
> srcu_idx = srcu_read_lock(&uprobes_srcu);
> list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node,
> srcu_read_lock_held(&uprobes_srcu)) {
> + /*
> + * If we don't find return consumer, it means uprobe consumer
> + * was added after we hit uprobe and return consumer did not
> + * get registered in which case we call the ret_handler only
> + * if it's not session consumer.
> + */
> + ric = return_consumer_find(ri, &iter, uc->id);
> + if (!ric && uc->session)
> + continue;
> if (uc->ret_handler)
> - uc->ret_handler(uc, ri->func, regs);
> + uc->ret_handler(uc, ri->func, regs, ric ? &ric->cookie : NULL);
> }
> srcu_read_unlock(&uprobes_srcu, srcu_idx);
> }
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index ac0a01cc8634..de241503c8fb 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -3332,7 +3332,8 @@ uprobe_multi_link_filter(struct uprobe_consumer *con, struct mm_struct *mm)
> }
>
> static int
> -uprobe_multi_link_handler(struct uprobe_consumer *con, struct pt_regs *regs)
> +uprobe_multi_link_handler(struct uprobe_consumer *con, struct pt_regs *regs,
> + __u64 *data)
> {
> struct bpf_uprobe *uprobe;
>
> @@ -3341,7 +3342,8 @@ uprobe_multi_link_handler(struct uprobe_consumer *con, struct pt_regs *regs)
> }
>
> static int
> -uprobe_multi_link_ret_handler(struct uprobe_consumer *con, unsigned long func, struct pt_regs *regs)
> +uprobe_multi_link_ret_handler(struct uprobe_consumer *con, unsigned long func, struct pt_regs *regs,
> + __u64 *data)
> {
> struct bpf_uprobe *uprobe;
>
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index f7443e996b1b..11103dde897b 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -88,9 +88,11 @@ static struct trace_uprobe *to_trace_uprobe(struct dyn_event *ev)
> static int register_uprobe_event(struct trace_uprobe *tu);
> static int unregister_uprobe_event(struct trace_uprobe *tu);
>
> -static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs);
> +static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs,
> + __u64 *data);
> static int uretprobe_dispatcher(struct uprobe_consumer *con,
> - unsigned long func, struct pt_regs *regs);
> + unsigned long func, struct pt_regs *regs,
> + __u64 *data);
>
> #ifdef CONFIG_STACK_GROWSUP
> static unsigned long adjust_stack_addr(unsigned long addr, unsigned int n)
> @@ -1500,7 +1502,8 @@ trace_uprobe_register(struct trace_event_call *event, enum trace_reg type,
> }
> }
>
> -static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs)
> +static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs,
> + __u64 *data)
> {
> struct trace_uprobe *tu;
> struct uprobe_dispatch_data udd;
> @@ -1530,7 +1533,8 @@ static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs)
> }
>
> static int uretprobe_dispatcher(struct uprobe_consumer *con,
> - unsigned long func, struct pt_regs *regs)
> + unsigned long func, struct pt_regs *regs,
> + __u64 *data)
> {
> struct trace_uprobe *tu;
> struct uprobe_dispatch_data udd;
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> index 1fc16657cf42..e91ff5b285f0 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> @@ -421,7 +421,7 @@ static struct bin_attribute bin_attr_bpf_testmod_file __ro_after_init = {
>
> static int
> uprobe_ret_handler(struct uprobe_consumer *self, unsigned long func,
> - struct pt_regs *regs)
> + struct pt_regs *regs, __u64 *data)
>
> {
> regs->ax = 0x12345678deadbeef;
> --
> 2.46.0
>

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