Re: [PATCH bpf-next 04/13] uprobes: Add arch_uprobe_verify_opcode function

[Andrii Nakryiko]

On Wed, Dec 11, 2024 at 5:34 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Adding arch_uprobe_verify_opcode function, so we can overload
> verification for each architecture in following changes.
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  include/linux/uprobes.h |  5 +++++
>  kernel/events/uprobes.c | 19 ++++++++++++++++---
>  2 files changed, 21 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index cc723bc48c1d..8843b7f99ed0 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -215,6 +215,11 @@ extern void uprobe_handle_trampoline(struct pt_regs *regs);
>  extern void *arch_uretprobe_trampoline(unsigned long *psize);
>  extern unsigned long uprobe_get_trampoline_vaddr(void);
>  extern void uprobe_copy_from_page(struct page *page, unsigned long vaddr, void *dst, int len);
> +extern int uprobe_verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode);
> +extern int arch_uprobe_verify_opcode(struct arch_uprobe *auprobe, struct page *page,
> +                                    unsigned long vaddr, uprobe_opcode_t *new_opcode,
> +                                    int nbytes);
> +extern bool arch_uprobe_is_register(uprobe_opcode_t *insn, int nbytes);
>  #else /* !CONFIG_UPROBES */
>  struct uprobes_state {
>  };
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 7c2ecf11a573..8068f91de9e3 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -263,7 +263,13 @@ static void uprobe_copy_to_page(struct page *page, unsigned long vaddr, const vo
>         kunmap_atomic(kaddr);
>  }
>
> -static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode)
> +__weak bool arch_uprobe_is_register(uprobe_opcode_t *insn, int nbytes)
> +{
> +       return is_swbp_insn(insn);

a bit weird that we ignore nbytes here... should we have nbytes ==
UPROBE_SWBP_INSN_SIZE check somewhere here or inside is_swbp_insn()?

> +}
> +
> +int uprobe_verify_opcode(struct page *page, unsigned long vaddr,
> +                        uprobe_opcode_t *new_opcode)
>  {
>         uprobe_opcode_t old_opcode;
>         bool is_swbp;
> @@ -291,6 +297,13 @@ static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t
>         return 1;
>  }
>
> +__weak int arch_uprobe_verify_opcode(struct arch_uprobe *auprobe, struct page *page,
> +                                    unsigned long vaddr, uprobe_opcode_t *new_opcode,
> +                                    int nbytes)
> +{
> +       return uprobe_verify_opcode(page, vaddr, new_opcode);

again, dropping nbytes on the floor here

> +}
> +
>  static struct delayed_uprobe *
>  delayed_uprobe_check(struct uprobe *uprobe, struct mm_struct *mm)
>  {
> @@ -479,7 +492,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
>         bool orig_page_huge = false;
>         unsigned int gup_flags = FOLL_FORCE;
>
> -       is_register = is_swbp_insn(insn);
> +       is_register = arch_uprobe_is_register(insn, nbytes);
>         uprobe = container_of(auprobe, struct uprobe, arch);
>
>  retry:
> @@ -490,7 +503,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
>         if (IS_ERR(old_page))
>                 return PTR_ERR(old_page);
>
> -       ret = verify_opcode(old_page, vaddr, insn);
> +       ret = arch_uprobe_verify_opcode(auprobe, old_page, vaddr, insn, nbytes);
>         if (ret <= 0)
>                 goto put_old;
>
> --
> 2.47.0
>