Re: [PATCH] uprobes: Restore original return address in uretprobe context

[Google]

On Fri, 17 Jul 2026 16:23:31 +0800
daichengrong <daichengrong@xxxxxxxxxxx> wrote:

> uretprobe replaces the original return address of a probed function with
> a trampoline address to capture function return events.
> 
> After the trampoline is entered and the uretprobe handler completes, the
> original return address needs to be restored in the user register context
> to keep the register state consistent with the state before probing.
> 
> Add an architecture-specific hook for restoring the original return
> address during uretprobe handling.
> 
> The initial implementation adds support for RISC-V. Other architectures
> keep the default empty implementation until their corresponding restore
> logic is implemented.
> 
> Signed-off-by: daichengrong <daichengrong@xxxxxxxxxxx>
> ---
>  arch/riscv/kernel/probes/uprobes.c | 7 +++++++
>  include/linux/uprobes.h            | 1 +
>  kernel/events/uprobes.c            | 5 +++++
>  3 files changed, 13 insertions(+)
> 
> diff --git a/arch/riscv/kernel/probes/uprobes.c b/arch/riscv/kernel/probes/uprobes.c
> index eb177d0ce8ab..0b1b94d9683e 100644
> --- a/arch/riscv/kernel/probes/uprobes.c
> +++ b/arch/riscv/kernel/probes/uprobes.c
> @@ -139,6 +139,13 @@ arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr,
>  	return ra;
>  }
>  
> +void
> +arch_uretprobe_hijack_set_addr(unsigned long orig_ret_vaddr,
> +				  struct pt_regs *regs)

OK, but hijack may not be a good naming, what about
"arch_uretprobe_restore_return_address()"?

And I need RISC-V maintainer's review.

Thank you,

> +{
> +	regs->ra = orig_ret_vaddr;
> +}
> +
>  int arch_uprobe_exception_notify(struct notifier_block *self,
>  				 unsigned long val, void *data)
>  {
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index f548fea2adec..2d0dc919845d 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -230,6 +230,7 @@ extern bool arch_uprobe_xol_was_trapped(struct task_struct *tsk);
>  extern int  arch_uprobe_exception_notify(struct notifier_block *self, unsigned long val, void *data);
>  extern void arch_uprobe_abort_xol(struct arch_uprobe *aup, struct pt_regs *regs);
>  extern unsigned long arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs *regs);
> +extern void arch_uretprobe_hijack_set_addr(unsigned long orig_ret_vaddr, struct pt_regs *regs);
>  extern bool arch_uretprobe_is_alive(struct return_instance *ret, enum rp_check ctx, struct pt_regs *regs);
>  extern bool arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs);
>  extern void arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 4084e926e284..deecaae01ab7 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1748,6 +1748,10 @@ void * __weak arch_uretprobe_trampoline(unsigned long *psize)
>  	return &insn;
>  }
>  
> +void __weak arch_uretprobe_hijack_set_addr(unsigned long orig_ret_vaddr, struct pt_regs *regs)
> +{
> +}
> +
>  static struct xol_area *__create_xol_area(unsigned long vaddr)
>  {
>  	struct mm_struct *mm = current->mm;
> @@ -2659,6 +2663,7 @@ void uprobe_handle_trampoline(struct pt_regs *regs)
>  		valid = !next_chain || arch_uretprobe_is_alive(next_chain, RP_CHECK_RET, regs);
>  
>  		instruction_pointer_set(regs, ri->orig_ret_vaddr);
> +		arch_uretprobe_hijack_set_addr(ri->orig_ret_vaddr, regs);
>  		do {
>  			/* pop current instance from the stack of pending return instances,
>  			 * as it's not pending anymore: we just fixed up original
> -- 
> 2.25.1
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>