Re: [PATCH RFCv3 08/23] uprobes/x86: Add uprobe syscall to speed up uprobe

[Andrii Nakryiko]

On Thu, Mar 20, 2025 at 4:43 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Adding new uprobe syscall that calls uprobe handlers for given
> 'breakpoint' address.
>
> The idea is that the 'breakpoint' address calls the user space
> trampoline which executes the uprobe syscall.
>
> The syscall handler reads the return address of the initial call
> to retrieve the original 'breakpoint' address. With this address
> we find the related uprobe object and call its consumers.
>
> Adding the arch_uprobe_trampoline_mapping function that provides
> uprobe trampoline mapping. This mapping is backed with one global
> page initialized at __init time and shared by the all the mapping
> instances.
>
> We do not allow to execute uprobe syscall if the caller is not
> from uprobe trampoline mapping.
>
> The uprobe syscall ensures the consumer (bpf program) sees registers
> values in the state before the trampoline was called.
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  arch/x86/entry/syscalls/syscall_64.tbl |   1 +
>  arch/x86/kernel/uprobes.c              | 134 +++++++++++++++++++++++++
>  include/linux/syscalls.h               |   2 +
>  include/linux/uprobes.h                |   1 +
>  kernel/events/uprobes.c                |  22 ++++
>  kernel/sys_ni.c                        |   1 +
>  6 files changed, 161 insertions(+)
>

[...]

> +void handle_syscall_uprobe(struct pt_regs *regs, unsigned long bp_vaddr)
> +{
> +       struct uprobe *uprobe;
> +       int is_swbp;
> +
> +       rcu_read_lock_trace();
> +       uprobe = find_active_uprobe_rcu(bp_vaddr, &is_swbp);
> +       if (!uprobe)
> +               goto unlock;
> +
> +       if (!get_utask())
> +               goto unlock;
> +
> +       if (arch_uprobe_ignore(&uprobe->arch, regs))
> +               goto unlock;
> +
> +       handler_chain(uprobe, regs);
> +
> + unlock:
> +       rcu_read_unlock_trace();

we now have `guard(rcu_tasks_trace)();`, let's use that in this
function, seems like a good fit?


> +}
> +
>  /*
>   * Perform required fix-ups and disable singlestep.
>   * Allow pending signals to take effect.
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index c00a86931f8c..bf5d05c635ff 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -392,3 +392,4 @@ COND_SYSCALL(setuid16);
>  COND_SYSCALL(rseq);
>
>  COND_SYSCALL(uretprobe);
> +COND_SYSCALL(uprobe);
> --
> 2.49.0
>