Re: [PATCH v5 0/5] Implement STRICT_MODULE_RWX for powerpc

Russell Currey
2019-10-31T00:09:49Z

On Wed, 2019-10-30 at 09:58 +0100, Christophe Leroy wrote:
>
> Le 30/10/2019 à 08:31, Russell Currey a écrit :
> > v4 cover letter:
> > https://lists.ozlabs.org/pipermail/linuxppc-dev/2019-October/198268.html
> > v3 cover letter:
> > https://lists.ozlabs.org/pipermail/linuxppc-dev/2019-October/198023.html
> >
> > Changes since v4:
> > [1/5]: Addressed review comments from Michael Ellerman
> > (thanks!)
> > [4/5]: make ARCH_HAS_STRICT_MODULE_RWX depend on
> > ARCH_HAS_STRICT_KERNEL_RWX to simplify things and avoid
> > STRICT_MODULE_RWX being *on by default* in cases where
> > STRICT_KERNEL_RWX is *unavailable*
> > [5/5]: split skiroot_defconfig changes out into its own patch
> >
> > The whole Kconfig situation is really weird and confusing, I
> > believe the
> > correct resolution is to change arch/Kconfig but the consequences
> > are so
> > minor that I don't think it's worth it, especially given that I
> > expect
> > powerpc to have mandatory strict RWX Soon(tm).
>
> I'm not such strict RWX can be made mandatory due to the impact it
> has
> on some subarches:
> - On the 8xx, unless all areas are 8Mbytes aligned, there is a
> significant overhead on TLB misses. And Aligning everthing to 8M is
> a
> waste of RAM which is not acceptable on systems having very few RAM.
> - On hash book3s32, we are able to map the kernel BATs. With a few
> alignment constraints, we are able to provide STRICT_KERNEL_RWX. But
> we
> are unable to provide exec protection on page granularity. Only on
> 256Mbytes segments. So for modules, we have to have the vmspace X. It
> is
> also not possible to have a kernel area RO. Only user areas can be
> made RO.
>

Yes, sorry, this was thoughtless from me, since in my mind I was just
thinking about the platforms I primarily work on (book3s64).

> Christophe
>
> > Russell Currey (5):
> > powerpc/mm: Implement set_memory() routines
> > powerpc/kprobes: Mark newly allocated probes as RO
> > powerpc/mm/ptdump: debugfs handler for W+X checks at runtime
> > powerpc: Set ARCH_HAS_STRICT_MODULE_RWX
> > powerpc/configs: Enable STRICT_MODULE_RWX in skiroot_defconfig
> >
> > arch/powerpc/Kconfig | 2 +
> > arch/powerpc/Kconfig.debug | 6 +-
> > arch/powerpc/configs/skiroot_defconfig | 1 +
> > arch/powerpc/include/asm/set_memory.h | 32 +++++++++++
> > arch/powerpc/kernel/kprobes.c | 3 +
> > arch/powerpc/mm/Makefile | 1 +
> > arch/powerpc/mm/pageattr.c | 77
> > ++++++++++++++++++++++++++
> > arch/powerpc/mm/ptdump/ptdump.c | 21 ++++++-
> > 8 files changed, 140 insertions(+), 3 deletions(-)
> > create mode 100644 arch/powerpc/include/asm/set_memory.h
> > create mode 100644 arch/powerpc/mm/pageattr.c
> >