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Subject: Re: [PATCH] ubsan: mark ubsan_type_mismatch_common inline
To:     Arnd Bergmann <arnd@arndb.de>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "# 3.4.x" <stable@vger.kernel.org>
References: <20190617123109.667090-1-arnd@arndb.de>
 <20190617140210.GB3436@hirez.programming.kicks-ass.net>
 <CAK8P3a3iwWOkMBL-H3h5aSaHKjKWFce22rvydvVE=3uMfeOhVg@mail.gmail.com>
From:   Andrey Ryabinin <aryabinin@virtuozzo.com>
Message-ID: <fc10bc69-0628-59eb-c243-9cd1dd3b47a4@virtuozzo.com>
Date:   Tue, 18 Jun 2019 16:27:45 +0300
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On 6/18/19 3:56 PM, Arnd Bergmann wrote:
> On Mon, Jun 17, 2019 at 4:02 PM Peter Zijlstra <peterz@infradead.org> wrote:
>>
>> On Mon, Jun 17, 2019 at 02:31:09PM +0200, Arnd Bergmann wrote:
>>> objtool points out a condition that it does not like:
>>>
>>> lib/ubsan.o: warning: objtool: __ubsan_handle_type_mismatch()+0x4a: call to stackleak_track_stack() with UACCESS enabled
>>> lib/ubsan.o: warning: objtool: __ubsan_handle_type_mismatch_v1()+0x4a: call to stackleak_track_stack() with UACCESS enabled
>>>
>>> I guess this is related to the call ubsan_type_mismatch_common()
>>> not being inline before it calls user_access_restore(), though
>>> I don't fully understand why that is a problem.
>>
>> The rules are that when AC is set, one is not allowed to CALL schedule,
>> because scheduling does not save/restore AC.  Preemption, through the
>> exceptions is fine, because the exceptions do save/restore AC.
>>
>> And while most functions do not appear to call into schedule, function
>> trace ensures that every single call does in fact call into schedule.
>> Therefore any CALL (with AC set) is invalid.
> 
> I see that stackleak_track_stack is already marked 'notrace',
> since we must ensure we don't recurse when calling into it from
> any of the function trace logic.
> 
> Does that mean we could just mark it as another safe call?
> 
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -486,6 +486,7 @@ static const char *uaccess_safe_builtin[] = {
>         "__ubsan_handle_type_mismatch",
>         "__ubsan_handle_type_mismatch_v1",
>         /* misc */
> +       "stackleak_track_stack",
>         "csum_partial_copy_generic",
>         "__memcpy_mcsafe",
>         "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
> 
> 
>> Maybe we should disable stackleak when building ubsan instead? We
>> already disable stack-protector when building ubsan.
> 
> I couldn't find out how that is done.
> 

I guess this:
ccflags-y += $(DISABLE_STACKLEAK_PLUGIN)