linux-kernel - Re: [PATCH 5/6] objtool: Add UACCESS validation

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Message-ID: <CAHk-=whzSnbX68x8PU1uRTqdLbKHHMUEBgx=fYAAeb7c7nF4Mw@mail.gmail.com>
Date:   Mon, 25 Feb 2019 09:34:17 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Julien Thierry <julien.thierry@....com>,
        Will Deacon <will.deacon@....com>,
        Ingo Molnar <mingo@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>, valentin.schneider@....com,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] objtool: Add UACCESS validation

On Mon, Feb 25, 2019 at 9:15 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> Ah, so the thing we need for inline-asm is %=, but Linus didn't like it:

Well, to be fair, I also didn't like the random big numbers.

I think that inline asm that has local labels should just use simple
enumeration, and always use the direction suffix to make those local
labels be unambiguous.

Now, there are cases where we may not be able to do that, because we
have internal macros within the asm that _also_ wants to do its own
numbers. This isn't such a case.

For that case, you might actually want to use a fancy "get me a unique
number and prefix", but it should be seen as the exception rather than
the first solution, because the code starts looking really random.

             Linus