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

[daichengrong <daichengrong@iscas.ac.cn>]

On 7/23/26 08:31, Masami Hiramatsu (Google) wrote:
> On Fri, 17 Jul 2026 16:23:31 +0800
> daichengrong <daichengrong@iscas.ac.cn> 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@iscas.ac.cn>
>> ---
>>  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()"?

Thanks for the suggestion.

I’ve renamed the function in v2 as suggested:

https://lore.kernel.org/all/20260810080140.96587-1-daichengrong@iscas.ac.cn/

Thanks,

> 
> 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
>>
>>
> 
> 


-- 
Chengrong