Re: [PATCH RFCv2 06/18] uprobes: Add orig argument to uprobe_write and uprobe_write_opcode

Andrii Nakryiko
2025-02-28T19:07:52Z

On Mon, Feb 24, 2025 at 6:03 AM 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.
>
> In following changes we want to use uprobe_write function for multiple
> updates, so adding new function argument to denote that this is the
> original instruction update. This way uprobe_write can make appropriate
> checks and restore the original page when possible.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> arch/arm/probes/uprobes/core.c | 2 +-
> include/linux/uprobes.h | 5 +++--
> kernel/events/uprobes.c | 22 ++++++++++------------
> 3 files changed, 14 insertions(+), 15 deletions(-)
>

[...]

> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index ad5879fc2d26..2b542043089e 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -471,25 +471,23 @@ static int update_ref_ctr(struct uprobe *uprobe, struct mm_struct *mm,
> * Return 0 (success) or a negative errno.
> */
> int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> - unsigned long vaddr, uprobe_opcode_t opcode)
> + unsigned long vaddr, uprobe_opcode_t opcode, bool orig)
> {
> - return uprobe_write(auprobe, mm, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE, verify_opcode);
> + return uprobe_write(auprobe, mm, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE, verify_opcode, orig);
> }
>
> int uprobe_write(struct arch_uprobe *auprobe, struct mm_struct *mm,
> unsigned long vaddr, uprobe_opcode_t *insn,
> - int nbytes, uprobe_write_verify_t verify)
> + int nbytes, uprobe_write_verify_t verify, bool orig)

why not call orig -> is_register and avoid a bunch of code churn?...
(and while "is_register" is not awesome name, still a bit more clear
compared to "orig", IMO)

> {
> struct page *old_page, *new_page;
> struct vm_area_struct *vma;
> - int ret, is_register;
> + int ret;
> bool orig_page_huge = false;
> unsigned int gup_flags = FOLL_FORCE;
>
> - is_register = is_swbp_insn(insn);
> - …