Re: [PATCHv2 bpf-next 1/3] bpf: Add support for bpf_get_func_ip helper for uprobe program

Yonghong Song
2023-08-03T15:51:09Z

On 8/3/23 2:52 AM, Jiri Olsa wrote:
> Adding support for bpf_get_func_ip helper for uprobe program to return
> probed address for both uprobe and return uprobe.
>
> We discussed this in [1] and agreed that uprobe can have special use
> of bpf_get_func_ip helper that differs from kprobe.
>
> The kprobe bpf_get_func_ip returns:
> - address of the function if probe is attach on function entry
> for both kprobe and return kprobe
> - 0 if the probe is not attach on function entry
>
> The uprobe bpf_get_func_ip returns:
> - address of the probe for both uprobe and return uprobe
>
> The reason for this semantic change is that kernel can't really tell
> if the probe user space address is function entry.
>
> The uprobe program is actually kprobe type program attached as uprobe.
> One of the consequences of this design is that uprobes do not have its
> own set of helpers, but share them with kprobes.
>
> As we need different functionality for bpf_get_func_ip helper for uprobe,
> I'm adding the bool value to the bpf_trace_run_ctx, so the helper can
> detect that it's executed in uprobe context and call specific code.
>
> The is_uprobe bool is set as true in bpf_prog_run_array_sleepable, which
> is currently used only for executing bpf programs in uprobe.
>
> Renaming bpf_prog_run_array_sleepable to bpf_prog_run_array_uprobe
> to address that it's only used for uprobes and that it sets the
> run_ctx.is_uprobe as suggested by Yafang Shao.
>
> Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> Tested-by: Alan Maguire <alan.maguire@oracle.com>
> [1] https://lore.kernel.org/bpf/CAEf4BzZ=xLVkG5eurEuvLU79wAMtwho7ReR+XJAgwhFF4M-7Cg@mail.gmail.com/
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> include/linux/bpf.h | 9 +++++++--
> include/uapi/linux/bpf.h | 7 ++++++-
> kernel/trace/bpf_trace.c | 21 ++++++++++++++++++++-
> kernel/trace/trace_probe.h | 5 +++++
> kernel/trace/trace_uprobe.c | 7 +------
> tools/include/uapi/linux/bpf.h | 7 ++++++-
> 6 files changed, 45 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index abe75063630b..db3fe5a61b05 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1819,6 +1819,7 @@ struct bpf_cg_run_ctx {
> struct bpf_trace_run_ctx {
> struct bpf_run_ctx run_ctx;
> u64 bpf_cookie;
> + bool is_uprobe;
> };
>
> struct bpf_tramp_run_ctx {
> @@ -1867,6 +1868,8 @@ bpf_prog_run_array(const struct bpf_prog_array *array,
> if (unlikely(!array))
> return ret;
>
> + run_ctx.is_uprobe = false;
> +
> migrate_disable();
> old_run_ctx = bpf_set_run_ctx(&run_ctx.run_ctx);
> item = &array->items[0];
> @@ -1891,8 +1894,8 @@ bpf_prog_run_array(const struct bpf_prog_array *array,
> * rcu-protected dynamically sized maps.
> */
> static __always_inline u32
> -bpf_prog_run_array_sleepable(const struct bpf_prog_array __rcu *array_rcu,
> - const void *ctx, bpf_prog_run_fn run_prog)
> +bpf_prog_run_array_uprobe(const struct bpf_prog_array __rcu *array_rcu,
> + const void *ctx, bpf_prog_run_fn run_prog)
> {
> const struct bpf_prog_array_item *item;
> const struct bpf_prog *prog;
> @@ -1906,6 +1909,8 @@ bpf_prog_run_array_sleepable(const struct bpf_prog_array __rcu *array_rcu,
> rcu_read_lock_trace();
> migrate_disable();
>
> + run_ctx.is_uprobe = true;
> +
> array = rcu_dereference_check(array_rcu, rcu_read_lock_trace_held());
> if (unlikely(!array))
> goto out;
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 70da85200695..d21deb46f49f 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5086,9 +5086,14 @@ union bpf_attr {
> * u64 bpf_get_func_ip(void *ctx)
> * Description
> * Get address of the traced function (for tracing and kprobe programs).
> + *
> + * When called for kprobe program attached as uprobe it returns
> + * probe address for both entry and return uprobe.
> + *
> * Return
> - * Address of the traced function.
> + * Address of the traced function for kprobe.
> * 0 for kprobes placed within the function (not at the entry).
> + * Address of the probe for uprobe and return uprobe.
> *
> * u64 bpf_get_attach_cookie(void *ctx)
> * Description
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 83bde2475ae5..d35f9750065a 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1046,9 +1046,28 @@ static unsigned long get_entry_ip(unsigned long fentry_ip)
> #define get_entry_ip(fentry_ip) fentry_ip
> #endif
>
> +#ifdef CONFIG_UPROBES
> +static unsigned long bpf_get_func_ip_uprobe(struct pt_regs *regs)
> +{
> + struct uprobe_dispatch_data *udd;
> +
> + udd = (struct uprobe_dispatch_data *) current->utask->vaddr;
> + return udd->bp_addr;
> +}
> +#else
> +#define bpf_get_func_ip_uprobe(regs) (u64) -EOPNOTSUPP
> +#endif

If I understand correctly, if below run_ctx->is_uprobe is true,
then bpf_get_func_ip_uprobe() func in the above will be called.
If run_ctx->is_uprobe is false, the above bpf_get_func_ip_uprobe
macro will be not be called. The that macro definition with
-EOPNOTSUPP really does not matter.

To avoid the above confusion, maybe we should put the CONFIG_UPROBES
inside bpf_get_func_ip_kprobe like below.

> +
> BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
> {
> - struct kprobe *kp = kprobe_running();
> + struct bpf_trace_run_ctx *run_ctx;
> + struct kprobe *kp;
> +
> + run_ctx = container_of(current->bpf_ctx, struct bpf_trace_run_ctx, run_ctx);
> + if (run_ctx->is_uprobe)
> + return bpf_get_func_ip_uprobe(regs);
> +
> + kp = kprobe_running();

...
struct bpf_trace_run_ctx *run_ctx __maybe_unused;
...

#ifdef CONFIG_UPROBES
run_ctx = container_of(current->bpf_ctx, struct bpf_trace_run_ctx,
run_ctx);
if (run_ctx->is_uprobe)
return ((struct uprobe_dispatch_data *)current->utask->vaddr)->bp_addr;
#endif

What do you think?

>
> if (!kp || !(kp->flags & KPROBE_FLAG_ON_FUNC_ENTRY))
> return 0;
> diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> index 01ea148723de..7dde806be91e 100644
> --- a/kernel/trace/trace_probe.h
> +++ b/kernel/trace/trace_probe.h
> @@ -519,3 +519,8 @@ void __trace_probe_log_err(int offset, int err);
>
> #define trace_probe_log_err(offs, err) \
> __trace_probe_log_err(offs, TP_ERR_##err)
> +
> +struct uprobe_dispatch_data {
> + struct trace_uprobe *tu;
> + unsigned long bp_addr;
> +};
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 555c223c3232..576b3bcb8ebd 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -88,11 +88,6 @@ 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);
>
> -struct uprobe_dispatch_data {
> - struct trace_uprobe *tu;
> - unsigned long bp_addr;
> -};
> -
> 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);
> @@ -1352,7 +1347,7 @@ static void __uprobe_perf_func(struct trace_uprobe *tu,
> if (bpf_prog_array_valid(call)) {
> u32 ret;
>
> - ret = bpf_prog_run_array_sleepable(call->prog_array, regs, bpf_prog_run);
> + ret = bpf_prog_run_array_uprobe(call->prog_array, regs, bpf_prog_run);
> if (!ret)
> return;
> }
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 70da85200695..d21deb46f49f 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -5086,9 +5086,14 @@ union bpf_attr {
> * u64 bpf_get_func_ip(void *ctx)
> * Description
> * Get address of the traced function (for tracing and kprobe programs).
> + *
> + * When called for kprobe program attached as uprobe it returns
> + * probe address for both entry and return uprobe.
> + *
> * Return
> - * Address of the traced function.
> + * Address of the traced function for kprobe.
> * 0 for kprobes placed within the function (not at the entry).
> + * Address of the probe for uprobe and return uprobe.
> *
> * u64 bpf_get_attach_cookie(void *ctx)
> * Description