linux-kernel - Re: [PATCH 12/13] x86/jitalloc: prepare to allocate exectuatble memory as ROX

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Date:   Thu, 1 Jun 2023 17:02:16 -0700
From:   Song Liu <song@...nel.org>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "David S. Miller" <davem@...emloft.net>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Helge Deller <deller@....de>,
        Huacai Chen <chenhuacai@...nel.org>,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Russell King <linux@...linux.org.uk>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, bpf@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-modules@...r.kernel.org,
        linux-parisc@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, loongarch@...ts.linux.dev,
        netdev@...r.kernel.org, sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 12/13] x86/jitalloc: prepare to allocate exectuatble
 memory as ROX

On Thu, Jun 1, 2023 at 4:07 AM Mike Rapoport <rppt@...nel.org> wrote:
>
> On Thu, Jun 01, 2023 at 12:30:50PM +0200, Peter Zijlstra wrote:
> > On Thu, Jun 01, 2023 at 01:12:56PM +0300, Mike Rapoport wrote:
> >
> > > +static void __init_or_module do_text_poke(void *addr, const void *opcode, size_t len)
> > > +{
> > > +   if (system_state < SYSTEM_RUNNING) {
> > > +           text_poke_early(addr, opcode, len);
> > > +   } else {
> > > +           mutex_lock(&text_mutex);
> > > +           text_poke(addr, opcode, len);
> > > +           mutex_unlock(&text_mutex);
> > > +   }
> > > +}
> >
> > So I don't much like do_text_poke(); why?
>
> I believe the idea was to keep memcpy for early boot before the kernel
> image is protected without going and adding if (is_module_text_address())
> all over the place.
>
> I think this can be used instead without updating all the call sites of
> text_poke_early():
>
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 91057de8e6bc..f994e63e9903 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -1458,7 +1458,7 @@ void __init_or_module text_poke_early(void *addr, const void *opcode,
>                  * code cannot be running and speculative code-fetches are
>                  * prevented. Just change the code.
>                  */
> -               memcpy(addr, opcode, len);
> +               text_poke_copy(addr, opcode, len);
>         } else {
>                 local_irq_save(flags);
>                 memcpy(addr, opcode, len);
>

This alone doesn't work, as text_poke_early() is called
before addr is added to the list of module texts. So we
still use memcpy() here.

Thanks,
Song