[PATCH v10 05/10] powerpc/bpf: Write protect JIT code

[Michael Ellerman]

Jordan Niethe <jniethe5 at gmail.com> writes:
> On Wed, Mar 31, 2021 at 9:37 PM Michael Ellerman <mpe at ellerman.id.au> wrote:
>>
>> Jordan Niethe <jniethe5 at gmail.com> writes:
>>
>> > Once CONFIG_STRICT_MODULE_RWX is enabled there will be no need to
>> > override bpf_jit_free() because it is now possible to set images
>> > read-only. So use the default implementation.
>> >
>> > Also add the necessary call to bpf_jit_binary_lock_ro() which will
>> > remove write protection and add exec protection to the JIT image after
>> > it has finished being written.
>> >
>> > Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
>> > ---
>> > v10: New to series
>> > ---
>> >  arch/powerpc/net/bpf_jit_comp.c   | 5 ++++-
>> >  arch/powerpc/net/bpf_jit_comp64.c | 4 ++++
>> >  2 files changed, 8 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
>> > index e809cb5a1631..8015e4a7d2d4 100644
>> > --- a/arch/powerpc/net/bpf_jit_comp.c
>> > +++ b/arch/powerpc/net/bpf_jit_comp.c
>> > @@ -659,12 +659,15 @@ void bpf_jit_compile(struct bpf_prog *fp)
>> >               bpf_jit_dump(flen, proglen, pass, code_base);
>> >
>> >       bpf_flush_icache(code_base, code_base + (proglen/4));
>> > -
>> >  #ifdef CONFIG_PPC64
>> >       /* Function descriptor nastiness: Address + TOC */
>> >       ((u64 *)image)[0] = (u64)code_base;
>> >       ((u64 *)image)[1] = local_paca->kernel_toc;
>> >  #endif
>> > +     if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX)) {
>> > +             set_memory_ro((unsigned long)image, alloclen >> PAGE_SHIFT);
>> > +             set_memory_x((unsigned long)image, alloclen >> PAGE_SHIFT);
>> > +     }
>>
>> You don't need to check the ifdef in a caller, there are stubs that
>> compile to nothing when CONFIG_ARCH_HAS_SET_MEMORY=n.

> As Christophe pointed out we could have !CONFIG_STRICT_MODULE_RWX and
> CONFIG_ARCH_HAS_SET_MEMORY which would then be wrong here.
> Probably we could make CONFIG_ARCH_HAS_SET_MEMORY depend on
> CONFIG_STRICT_MODULE_RWX?

I thought it already did depend on it :)

That seems a reasonable dependency to me.

cheers