linux-kernel - Re: objtool warning from next-20230125

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Message-ID: <Y9PAN12SPHuGL99G@hirez.programming.kicks-ass.net>
Date:   Fri, 27 Jan 2023 13:14:47 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        linux-kernel@...r.kernel.org, sfr@...b.auug.org.au
Subject: Re: objtool warning from next-20230125

On Thu, Jan 26, 2023 at 12:59:54PM -0800, Josh Poimboeuf wrote:
> On Thu, Jan 26, 2023 at 10:23:02AM -0800, Paul E. McKenney wrote:
> > Hello!
> > 
> > I have started seeing these objtool warnings from a wide variety of
> > KASAN-enabled rcutorture-related test scenarios in next-20230125.  It has
> > been awhile since I tested -next, so I am not yet sure where this started.
> > 
> > vmlinux.o: warning: objtool: __asan_memset+0x34: call to __memset() with UACCESS enabled
> > vmlinux.o: warning: objtool: __asan_memmove+0x4d: call to __memmove() with UACCESS enabled
> > vmlinux.o: warning: objtool: __asan_memcpy+0x4d: call to __memcpy() with UACCESS enabled
> > 
> > As usual, should I be worried?
> 
> This apparently came from Peter's
> 
>   69d4c0d32186 ("entry, kasan, x86: Disallow overriding mem*() functions")
> 
> but I have no idea how this is supposed to work.  Peter?

Durr.. I'm not sure why I put them in the uaccess_safe_builtin[] array.

So yeah, this reproduces using defconfig+KASAN, removing the functions
from the array shuts it up and doesn't generate new ones -- for that
config.

Let me try and build a few more .configs...