linux-kernel - Re: [PATCH v2 3/5] signal: Add unsafe_copy_siginfo_to

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Date:   Thu, 2 Sep 2021 09:05:05 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 3/5] signal: Add unsafe_copy_siginfo_to_user()

On Wed, Sep 1, 2021 at 11:55 PM Christoph Hellwig <hch@...radead.org> wrote:
>
> I'm a little worried about all these unsafe helper in powerpc and the
> ever increasing scope of the unsafe sections.  Can you at least at
> powerpc support to objtool to verify them?  objtool verifications has
> helped to find quite a few bugs in unsafe sections on x86.

.. yeah, objdump was particularly useful for the really subtle ones
where there are random function calls due to things like KASAN etc.

No human would ever have noticed "oh, we're walking the kernel stack
with user mode accesses enabled because the compiler inserted magical
debug code here". Objdump sees those things - assuming you teach it
about that special user space access enable/disable sequence.

            Linus