linux-kernel - Re: [PATCH 2/2] arm64/module: Use text-poke API for late relocations.

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Message-ID: <CAMuHMdU-1f3_ufKzHxg7KP-oQOTUR=P3e36W9X=+nkA4SH1F_Q@mail.gmail.com>
Date: Fri, 11 Apr 2025 08:31:25 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Dylan Hatch <dylanbhatch@...gle.com>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	"Mike Rapoport (Microsoft)" <rppt@...nel.org>, Arnd Bergmann <arnd@...db.de>, Luis Chamberlain <mcgrof@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Song Liu <song@...nel.org>, 
	Ard Biesheuvel <ardb@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Roman Gushchin <kfree@...gle.com>
Subject: Re: [PATCH 2/2] arm64/module: Use text-poke API for late relocations.

Hi Dylan,

Thanks for your patch!

On Thu, 10 Apr 2025 at 22:06, Dylan Hatch <dylanbhatch@...gle.com> wrote:
> To enable late module patching, livepatch modules need to be able to
> apply some of their relocations well after being loaded. In this
> scenario, use the text-poking API to allow this, even with
> STRICT_MODULE_RWX.

Wouldn't using the text-poking API involve calling text_poke()?

> This patch is largely based off commit 88fc078a7a8f6 ("x86/module: Use
> text_poke() for late relocations").
>
> Signed-off-by: Dylan Hatch <dylanbhatch@...gle.com>

> --- a/arch/arm64/kernel/module.c
> +++ b/arch/arm64/kernel/module.c

> @@ -431,6 +444,30 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
>         return -ENOEXEC;
>  }
>
> +int apply_relocate_add(Elf64_Shdr *sechdrs,
> +                      const char *strtab,
> +                      unsigned int symindex,
> +                      unsigned int relsec,
> +                      struct module *me)
> +{
> +       int ret;
> +       bool early = me->state == MODULE_STATE_UNFORMED;
> +       void *(*write)(void *, const void *, size_t) = memcpy;
> +
> +       if (!early) {
> +               write = aarch64_insn_copy;

Perhaps aarch64_insn_copy() should be renamed to text_poke(),  as it
is a wrapper around __text_poke(), just like the x86 implementation?

> +               mutex_lock(&text_mutex);
> +       }
> +
> +       ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
> +                                  write);
> +
> +       if (!early)
> +               mutex_unlock(&text_mutex);
> +
> +       return ret;
> +}
> +
>  static inline void __init_plt(struct plt_entry *plt, unsigned long addr)
>  {
>         *plt = get_plt_entry(addr, plt);

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds