Re: [PATCHv3 perf/core 06/22] uprobes: Add is_register argument to uprobe_write and uprobe_write_opcode

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

On Thu,  5 Jun 2025 15:23:33 +0200
Jiri Olsa <jolsa@kernel.org> wrote:

> The uprobe_write has special path to restore the original page when we
> write original instruction back. This happens when uprobe_write detects
> that we want to write anything else but breakpoint instruction.
> 
> Moving the detection away and passing it to uprobe_write as argument,
> so it's possible to write different instructions (other than just
> breakpoint and rest).

Looks good to me.

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

Thanks,


> 
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> Acked-by: Oleg Nesterov <oleg@redhat.com>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  arch/arm/probes/uprobes/core.c |  2 +-
>  include/linux/uprobes.h        |  5 +++--
>  kernel/events/uprobes.c        | 21 +++++++++++----------
>  3 files changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/arm/probes/uprobes/core.c b/arch/arm/probes/uprobes/core.c
> index 885e0c5e8c20..3d96fb41d624 100644
> --- a/arch/arm/probes/uprobes/core.c
> +++ b/arch/arm/probes/uprobes/core.c
> @@ -30,7 +30,7 @@ int set_swbp(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>  	     unsigned long vaddr)
>  {
>  	return uprobe_write_opcode(auprobe, vma, vaddr,
> -		   __opcode_to_mem_arm(auprobe->bpinsn));
> +		   __opcode_to_mem_arm(auprobe->bpinsn), true);
>  }
>  
>  bool arch_uprobe_ignore(struct arch_uprobe *auprobe, struct pt_regs *regs)
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 147c4a0a1af9..518b26756469 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -197,9 +197,10 @@ extern bool is_swbp_insn(uprobe_opcode_t *insn);
>  extern bool is_trap_insn(uprobe_opcode_t *insn);
>  extern unsigned long uprobe_get_swbp_addr(struct pt_regs *regs);
>  extern unsigned long uprobe_get_trap_addr(struct pt_regs *regs);
> -extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma, unsigned long vaddr, uprobe_opcode_t);
> +extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma, unsigned long vaddr, uprobe_opcode_t,
> +			       bool is_register);
>  extern int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma, const unsigned long opcode_vaddr,
> -			uprobe_opcode_t *insn, int nbytes, uprobe_write_verify_t verify);
> +			uprobe_opcode_t *insn, int nbytes, uprobe_write_verify_t verify, bool is_register);
>  extern struct uprobe *uprobe_register(struct inode *inode, loff_t offset, loff_t ref_ctr_offset, struct uprobe_consumer *uc);
>  extern int uprobe_apply(struct uprobe *uprobe, struct uprobe_consumer *uc, bool);
>  extern void uprobe_unregister_nosync(struct uprobe *uprobe, struct uprobe_consumer *uc);
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index f7feb7417a2c..1e5dc3b30707 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -402,10 +402,10 @@ static bool orig_page_is_identical(struct vm_area_struct *vma,
>  
>  static int __uprobe_write(struct vm_area_struct *vma,
>  		struct folio_walk *fw, struct folio *folio,
> -		unsigned long insn_vaddr, uprobe_opcode_t *insn, int nbytes)
> +		unsigned long insn_vaddr, uprobe_opcode_t *insn, int nbytes,
> +		bool is_register)
>  {
>  	const unsigned long vaddr = insn_vaddr & PAGE_MASK;
> -	const bool is_register = !!is_swbp_insn(insn);
>  	bool pmd_mappable;
>  
>  	/* For now, we'll only handle PTE-mapped folios. */
> @@ -488,26 +488,27 @@ static int __uprobe_write(struct vm_area_struct *vma,
>   * Return 0 (success) or a negative errno.
>   */
>  int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> -		const unsigned long opcode_vaddr, uprobe_opcode_t opcode)
> +		const unsigned long opcode_vaddr, uprobe_opcode_t opcode,
> +		bool is_register)
>  {
> -	return uprobe_write(auprobe, vma, opcode_vaddr, &opcode, UPROBE_SWBP_INSN_SIZE, verify_opcode);
> +	return uprobe_write(auprobe, vma, opcode_vaddr, &opcode, UPROBE_SWBP_INSN_SIZE,
> +			    verify_opcode, is_register);
>  }
>  
>  int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>  		 const unsigned long insn_vaddr, uprobe_opcode_t *insn, int nbytes,
> -		 uprobe_write_verify_t verify)
> +		 uprobe_write_verify_t verify, bool is_register)
>  {
>  	const unsigned long vaddr = insn_vaddr & PAGE_MASK;
>  	struct mm_struct *mm = vma->vm_mm;
>  	struct uprobe *uprobe;
> -	int ret, is_register, ref_ctr_updated = 0;
> +	int ret, ref_ctr_updated = 0;
>  	unsigned int gup_flags = FOLL_FORCE;
>  	struct mmu_notifier_range range;
>  	struct folio_walk fw;
>  	struct folio *folio;
>  	struct page *page;
>  
> -	is_register = is_swbp_insn(insn);
>  	uprobe = container_of(auprobe, struct uprobe, arch);
>  
>  	if (WARN_ON_ONCE(!is_cow_mapping(vma->vm_flags)))
> @@ -569,7 +570,7 @@ int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>  	/* Walk the page tables again, to perform the actual update. */
>  	if (folio_walk_start(&fw, vma, vaddr, 0)) {
>  		if (fw.page == page)
> -			ret = __uprobe_write(vma, &fw, folio, insn_vaddr, insn, nbytes);
> +			ret = __uprobe_write(vma, &fw, folio, insn_vaddr, insn, nbytes, is_register);
>  		folio_walk_end(&fw, vma);
>  	}
>  
> @@ -611,7 +612,7 @@ int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>  int __weak set_swbp(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>  		unsigned long vaddr)
>  {
> -	return uprobe_write_opcode(auprobe, vma, vaddr, UPROBE_SWBP_INSN);
> +	return uprobe_write_opcode(auprobe, vma, vaddr, UPROBE_SWBP_INSN, true);
>  }
>  
>  /**
> @@ -627,7 +628,7 @@ int __weak set_orig_insn(struct arch_uprobe *auprobe,
>  		struct vm_area_struct *vma, unsigned long vaddr)
>  {
>  	return uprobe_write_opcode(auprobe, vma, vaddr,
> -			*(uprobe_opcode_t *)&auprobe->insn);
> +			*(uprobe_opcode_t *)&auprobe->insn, false);
>  }
>  
>  /* uprobe should have guaranteed positive refcount */
> -- 
> 2.49.0
> 


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