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From:   Marco Elver <elver@google.com>
Date:   Tue, 9 Feb 2021 22:34:17 +0100
Message-ID: <CANpmjNOXjwiZpfzhi0Zu-gdQmwiK4dMiAE0ZhRcOnZaw00DaVA@mail.gmail.com>
Subject: Re: [PATCH mm] kfence: make reporting sensitive information configurable
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        Jann Horn <jannh@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Timur Tabi <timur@kernel.org>, Petr Mladek <pmladek@suse.cz>,
        Kees Cook <keescook@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>
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On Tue, 9 Feb 2021 at 19:06, Vlastimil Babka <vbabka@suse.cz> wrote:
> On 2/9/21 4:13 PM, Marco Elver wrote:
> > We cannot rely on CONFIG_DEBUG_KERNEL to decide if we're running a
> > "debug kernel" where we can safely show potentially sensitive
> > information in the kernel log.
> >
> > Therefore, add the option CONFIG_KFENCE_REPORT_SENSITIVE to decide if we
> > should add potentially sensitive information to KFENCE reports. The
> > default behaviour remains unchanged.
> >
> > Signed-off-by: Marco Elver <elver@google.com>
>
> Hi,
>
> could we drop this kconfig approach in favour of the boot option proposed here?
> [1] Just do the prints with %p unconditionally and the boot option takes care of
> it? Also Linus mentioned dislike of controlling potential memory leak to be a
> config option [2]
>
> Thanks,
> Vlastimil
>
> [1] https://lore.kernel.org/linux-mm/20210202213633.755469-1-timur@kernel.org/
> [2]
> https://lore.kernel.org/linux-mm/CAHk-=wgaK4cz=K-JB4p-KPXBV73m9bja2w1W1Lr3iu8+NEPk7A@mail.gmail.com/

Is the patch at [1] already in -next? If not I'll wait until it is,
because otherwise KFENCE reports will be pretty useless.

I think it is reasonable to switch to '%p' once we have the boot
option, but doing so while we do not yet have the option doesn't work
for us. We can potentially drop this patch if the boot option patch
will make it into mainline soon. Otherwise my preference would be to
take this patch and revert it with the switch to '%p' when the boot
option has landed.

Thanks,
-- Marco