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In-Reply-To: <87553048-5f1f-0704-2256-d2c85b8e43c6@csgroup.eu>
From: Jordan Niethe <jniethe5@gmail.com>
Date: Thu, 18 Mar 2021 13:42:04 +1100
Message-ID: <CACzsE9qm694GvaS+iZgd-X5sNwhHXsAxMdJD0n79fmehtt26PA@mail.gmail.com>
Subject: Re: [PATCH v9 3/8] powerpc/kprobes: Mark newly allocated probes as RO
To: Christophe Leroy <christophe.leroy@csgroup.eu>
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Cc: Christophe Leroy <christophe.leroy@c-s.fr>, ajd@linux.ibm.com,
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On Wed, Mar 17, 2021 at 5:12 PM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 16/03/2021 =C3=A0 04:17, Jordan Niethe a =C3=A9crit :
> > From: Russell Currey <ruscur@russell.cc>
> >
> > With CONFIG_STRICT_KERNEL_RWX=3Dy and CONFIG_KPROBES=3Dy, there will be=
 one
> > W+X page at boot by default.  This can be tested with
> > CONFIG_PPC_PTDUMP=3Dy and CONFIG_PPC_DEBUG_WX=3Dy set, and checking the
> > kernel log during boot.
> >
> > Add an arch specific insn page allocator which returns RO pages if
> > STRICT_KERNEL_RWX is enabled. This page is only written to with
> > patch_instruction() which is able to write RO pages.
> >
>
> Did you investigate BPF ? The problematic looks more or less similar to k=
probe:
>
> bpf_jit_compile() in arch/powerpc/net/bpf_jit_comp.c calls module_alloc()=
, which provides it with
> PAGE_KERNEL_TEXT memory, ie RWX. That function is only used on PPC32 whic=
h still has Classic BPF,
> and this is about to go away with future series
> https://patchwork.ozlabs.org/project/linuxppc-dev/cover/cover.1608112796.=
git.christophe.leroy@csgroup.eu/
>
> PPC64 has Extended BPF instead, and PPC32 will it the future too.
> bpf_int_jit_compile() in arch/powerpc/net/bpf_jit_comp64.c calls bpf_jit_=
binary_alloc() which uses
> bpf_jit_alloc_exec().
>
> bpf_jit_alloc_exec() is a weak function that should be redefined for powe=
rpc I think, more or less
> like alloc_insn_page() for kprobes.
Thanks, that is a good point. I will handle bpf with the next revision.
>
> Christophe