From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: Re: [RFC PATCH 1/9] kernel: add support for patchable function pointers
Date: Fri, 5 Oct 2018 16:03:53 +0200
Message-ID: <CAKv+Gu_GpeqvTHC0E341ehvbYVyEiXMxirijhFTJrwo0OMrdAg@mail.gmail.com>
References: <20181005081333.15018-1-ard.biesheuvel@linaro.org>
 <20181005081333.15018-2-ard.biesheuvel@linaro.org> <20181005135728.GR19272@hirez.programming.kicks-ass.net>
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Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Jason A . Donenfeld" <Jason@zx2c4.com>,
        Eric Biggers <ebiggers@kernel.org>,
        Samuel Neves <sneves@dei.uc.pt>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-f
To: Peter Zijlstra <peterz@infradead.org>
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On 5 October 2018 at 15:57, Peter Zijlstra <peterz@infradead.org> wrote:
> On Fri, Oct 05, 2018 at 10:13:25AM +0200, Ard Biesheuvel wrote:
>> Add a function pointer abstraction that can be implemented by the arch
>> in a manner that avoids the downsides of function pointers, i.e., the
>> fact that they are typically located in a writable data section, and
>> their vulnerability to Spectre like defects.
>>
>> The FFP (or fast function pointer) is callable as a function, since
>> the generic incarnation is simply that. However, due to the fact that
>> C does not distinguish between functions and function pointers at the
>> call site, the architecture can instead emit it as a patchable sequence
>> of instructions consisting of ordinary branches.
>
> This is basically a static_key, except for indirection function calls?

Yes, that is why I put you on cc :-)

> So why not call the thing static_func or static_call or something like
> that?

Yep that sounds better.