linux-kernel - Re: [PATCHv3 perf/core 04/22] uprobes: Add uprobe

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Message-Id: <20250625151229.d3f11622884fd6f4f09c4f62@kernel.org>
Date: Wed, 25 Jun 2025 15:12:29 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 x86@...nel.org, Song Liu <songliubraving@...com>, Yonghong Song
 <yhs@...com>, John Fastabend <john.fastabend@...il.com>, Hao Luo
 <haoluo@...gle.com>, Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Alan Maguire <alan.maguire@...cle.com>, David Laight
 <David.Laight@...LAB.COM>, Thomas Weißschuh
 <thomas@...ch.de>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCHv3 perf/core 04/22] uprobes: Add uprobe_write function

On Thu,  5 Jun 2025 15:23:31 +0200
Jiri Olsa <jolsa@...nel.org> wrote:

> Adding uprobe_write function that does what uprobe_write_opcode did
> so far, but allows to pass verify callback function that checks the
> memory location before writing the opcode.
> 
> It will be used in following changes to implement specific checking
> logic for instruction update.
> 
> The uprobe_write_opcode now calls uprobe_write with verify_opcode as
> the verify callback.
> 

Looks good to me.

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

Thanks,

> Acked-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  include/linux/uprobes.h |  5 +++++
>  kernel/events/uprobes.c | 14 ++++++++++----
>  2 files changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 7447e15559b8..e13382054435 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -187,6 +187,9 @@ struct uprobes_state {
>  	struct xol_area		*xol_area;
>  };
>  
> +typedef int (*uprobe_write_verify_t)(struct page *page, unsigned long vaddr,
> +				     uprobe_opcode_t *opcode);
> +
>  extern void __init uprobes_init(void);
>  extern int set_swbp(struct arch_uprobe *aup, struct vm_area_struct *vma, unsigned long vaddr);
>  extern int set_orig_insn(struct arch_uprobe *aup, struct vm_area_struct *vma, unsigned long vaddr);
> @@ -195,6 +198,8 @@ 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(struct arch_uprobe *auprobe, struct vm_area_struct *vma, const unsigned long opcode_vaddr,
> +			uprobe_opcode_t opcode, uprobe_write_verify_t verify);
>  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 37d3a3f6e48a..777de9b95dd7 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -399,7 +399,7 @@ static bool orig_page_is_identical(struct vm_area_struct *vma,
>  	return identical;
>  }
>  
> -static int __uprobe_write_opcode(struct vm_area_struct *vma,
> +static int __uprobe_write(struct vm_area_struct *vma,
>  		struct folio_walk *fw, struct folio *folio,
>  		unsigned long opcode_vaddr, uprobe_opcode_t opcode)
>  {
> @@ -488,6 +488,12 @@ static int __uprobe_write_opcode(struct vm_area_struct *vma,
>   */
>  int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>  		const unsigned long opcode_vaddr, uprobe_opcode_t opcode)
> +{
> +	return uprobe_write(auprobe, vma, opcode_vaddr, opcode, verify_opcode);
> +}
> +
> +int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> +		 const unsigned long opcode_vaddr, uprobe_opcode_t opcode, uprobe_write_verify_t verify)
>  {
>  	const unsigned long vaddr = opcode_vaddr & PAGE_MASK;
>  	struct mm_struct *mm = vma->vm_mm;
> @@ -510,7 +516,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>  	 * page that we can safely modify. Use FOLL_WRITE to trigger a write
>  	 * fault if required. When unregistering, we might be lucky and the
>  	 * anon page is already gone. So defer write faults until really
> -	 * required. Use FOLL_SPLIT_PMD, because __uprobe_write_opcode()
> +	 * required. Use FOLL_SPLIT_PMD, because __uprobe_write()
>  	 * cannot deal with PMDs yet.
>  	 */
>  	if (is_register)
> @@ -522,7 +528,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>  		goto out;
>  	folio = page_folio(page);
>  
> -	ret = verify_opcode(page, opcode_vaddr, &opcode);
> +	ret = verify(page, opcode_vaddr, &opcode);
>  	if (ret <= 0) {
>  		folio_put(folio);
>  		goto out;
> @@ -561,7 +567,7 @@ int uprobe_write_opcode(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_opcode(vma, &fw, folio, opcode_vaddr, opcode);
> +			ret = __uprobe_write(vma, &fw, folio, opcode_vaddr, opcode);
>  		folio_walk_end(&fw, vma);
>  	}
>  
> -- 
> 2.49.0
> 


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