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References: <20210316031741.1004850-1-jniethe5@gmail.com>
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From: Jordan Niethe <jniethe5@gmail.com>
Date: Wed, 17 Mar 2021 11:38:53 +1100
Message-ID: <CACzsE9rbgjNtLOjCHL9+LN6_Xoo6mJ_D5pewuMg7ktqA_OnR0w@mail.gmail.com>
Subject: Re: [PATCH v9 2/8] powerpc/lib/code-patching: Set up Strict RWX
 patching earlier
To: Christophe Leroy <christophe.leroy@csgroup.eu>
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Cc: Christophe Leroy <christophe.leroy@c-s.fr>, ajd@linux.ibm.com,
 Nicholas Piggin <npiggin@gmail.com>, naveen.n.rao@linux.ibm.com,
 linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, Daniel Axtens <dja@axtens.net>
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On Tue, Mar 16, 2021 at 5:32 PM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 16/03/2021 =C3=A0 04:17, Jordan Niethe a =C3=A9crit :
> > setup_text_poke_area() is a late init call so it runs before
> > mark_rodata_ro() and after the init calls. This lets all the init code
> > patching simply write to their locations. In the future, kprobes is
> > going to allocate its instruction pages RO which means they will need
> > setup_text__poke_area() to have been already called for their code
> > patching. However, init_kprobes() (which allocates and patches some
> > instruction pages) is an early init call so it happens before
> > setup_text__poke_area().
> >
> > start_kernel() calls poking_init() before any of the init calls. On
> > powerpc, poking_init() is currently a nop. setup_text_poke_area() relie=
s
> > on kernel virtual memory, cpu hotplug and per_cpu_areas being setup.
> > setup_per_cpu_areas(), boot_cpu_hotplug_init() and mm_init() are called
> > before poking_init().
> >
> > Turn setup_text_poke_area() into poking_init().
> >
> > Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> > ---
> > v9: New to series
> > ---
> >   arch/powerpc/lib/code-patching.c | 12 ++++--------
> >   1 file changed, 4 insertions(+), 8 deletions(-)
> >
> > diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-p=
atching.c
> > index 2333625b5e31..b28afa1133db 100644
> > --- a/arch/powerpc/lib/code-patching.c
> > +++ b/arch/powerpc/lib/code-patching.c
> > @@ -65,14 +65,11 @@ static int text_area_cpu_down(unsigned int cpu)
> >   }
> >
> >   /*
> > - * Run as a late init call. This allows all the boot time patching to =
be done
> > - * simply by patching the code, and then we're called here prior to
> > - * mark_rodata_ro(), which happens after all init calls are run. Altho=
ugh
> > - * BUG_ON() is rude, in this case it should only happen if ENOMEM, and=
 we judge
> > - * it as being preferable to a kernel that will crash later when someo=
ne tries
> > - * to use patch_instruction().
> > + * Although BUG_ON() is rude, in this case it should only happen if EN=
OMEM, and
> > + * we judge it as being preferable to a kernel that will crash later w=
hen
> > + * someone tries to use patch_instruction().
>
> Please use WARN_ON(), see why at https://www.kernel.org/doc/html/latest/p=
rocess/deprecated.html
Ok I can include a change to WARN_ON() as a separate patch.
>
> >    */
> > -static int __init setup_text_poke_area(void)
> > +int __init poking_init(void)
> >   {
> >       BUG_ON(!cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
> >               "powerpc/text_poke:online", text_area_cpu_up,
> > @@ -80,7 +77,6 @@ static int __init setup_text_poke_area(void)
> >
> >       return 0;
> >   }
> > -late_initcall(setup_text_poke_area);
> >
> >   /*
> >    * This can be called for kernel text or a module.
> >