linux-kernel - Re: [PATCH 1/8] kasan,x86: Frob kasan

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Date:   Wed, 6 Mar 2019 16:01:20 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Julien Thierry <julien.thierry@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        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>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: Re: [PATCH 1/8] kasan,x86: Frob kasan_report() in an exception

On Wed, Mar 6, 2019 at 3:56 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Mar 06, 2019 at 03:40:51PM +0100, Dmitry Vyukov wrote:
> > On Wed, Mar 6, 2019 at 3:34 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> > > mm/kasan/generic_report.o: warning: objtool: __asan_report_load1_noabort()+0x0: call to __fentry__() with UACCESS enabled
>
> > But if it makes things simpler for the objtool, then I think we can
> > disable function tracer for generic_report.c too.
>
> It's not simpler; it is actually a correctness issue. Those functions
> must not call into the tracer with AC=1

You are right!
I assumed they are defined in kasan.c and then call into a report
function that is compiled with -pg.
We can either disable -pg for report.c, or move these callbacks into
kasan.c which already has -pg disabled. I don't have strong preference
either way as long as the option works in all cases.