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Subject: Re: [PATCH 18/20] objtool: Add UACCESS validation
To:     Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>, Peter Anvin <hpa@zytor.com>,
        Julien Thierry <julien.thierry@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Ingo Molnar <mingo@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        James Morse <james.morse@arm.com>, valentin.schneider@arm.com,
        Brian Gerst <brgerst@gmail.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Andrew Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Steven Rostedt <rostedt@goodmis.org>
References: <20190307114511.870090179@infradead.org>
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 <CAHk-=wgKDSSoV5WvO018hoPPSHO=TQ3wwnfOtCpaENceBe0Z6Q@mail.gmail.com>
 <20190307174135.GJ32477@hirez.programming.kicks-ass.net>
From:   Andrey Ryabinin <aryabinin@virtuozzo.com>
Message-ID: <6a4875bd-2b22-91e4-cbe2-b01c12786a1b@virtuozzo.com>
Date:   Thu, 7 Mar 2019 23:15:42 +0300
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On 3/7/19 8:41 PM, Peter Zijlstra wrote:
> On Thu, Mar 07, 2019 at 08:33:26AM -0800, Linus Torvalds wrote:
>> On Thu, Mar 7, 2019 at 3:52 AM Peter Zijlstra <peterz@infradead.org> wrote:
>>>
>>> XXX: are we sure we want __memset marked AC-safe?
>>
>> It's certainly one of the safer functions to call with AC set, but it
>> sounds wrong anyway. It's not like it's likely to leak kernel data
>> (most memset's are with 0, and even the non-zero ones I can't imagine
>> are sensitive - more like poison values etc).
>>
>> What's the call site that made you go "just add __memset() to the list"?
> 
> __asan_{,un}poinson_stack_memory()

These two can be called only with CONFIG_KASAN_EXTRA=y which 
was removed very recently, so it should be safe to delete these functions.

>   kasan_{,un}poison_shadow()
>     __memset()
> 
>