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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Thu, 5 Dec 2019 12:36:56 +0100
Message-ID: <CACT4Y+bUkzJAezH9Pk=c1amtzO0-r1Hcn3WmDuS+Drn-R3GAQA@mail.gmail.com>
Subject: Re: KASAN: slab-out-of-bounds Read in fbcon_get_font
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        syzbot <syzbot+4455ca3b3291de891abc@syzkaller.appspotmail.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        DRI <dri-devel@lists.freedesktop.org>, ghalat@redhat.com,
        Gleb Natapov <gleb@kernel.org>, gwshan@linux.vnet.ibm.com,
        "H. Peter Anvin" <hpa@zytor.com>, James Morris <jmorris@namei.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        KVM list <kvm@vger.kernel.org>,
        Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-security-module <linux-security-module@vger.kernel.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Russell Currey <ruscur@russell.cc>,
        Sam Ravnborg <sam@ravnborg.org>,
        "Serge E. Hallyn" <serge@hallyn.com>, stewart@linux.vnet.ibm.com,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Kentaro Takeda <takedakn@nttdata.co.jp>,
        Thomas Gleixner <tglx@linutronix.de>,
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On Thu, Dec 5, 2019 at 11:41 AM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> On 2019/12/05 19:22, Paolo Bonzini wrote:
> > Ah, and because the machine is a KVM guest, kvm_wait appears in a lot of
> > backtrace and I get to share syzkaller's joy every time. :)
> >
> > This bisect result is bogus, though Tetsuo found the bug anyway.
> > Perhaps you can exclude commits that only touch architectures other than
> > x86?
> >
>
> It would be nice if coverage functionality can extract filenames in the source
> code and supply the list of filenames as arguments for bisect operation.
>
> Also, (unrelated but) it would be nice if we can have "make yes2modconfig"
> target which converts CONFIG_FOO=y to CONFIG_FOO=m if FOO is tristate.
> syzbot is testing kernel configs close to "make allyesconfig" but I want to
> save kernel rebuild time by disabling unrelated functionality when manually
> "debug printk()ing" kernels.

I thought that maybe sed "s#=y#=m#g" && make olddefconfig will do, but
unfortunately, it turns off non-tristate configs...

$ egrep "CONFIG_MEMORY_HOTPLUG|CONFIG_TCP_CONG_DCTCP" .config
CONFIG_MEMORY_HOTPLUG=y
CONFIG_TCP_CONG_DCTCP=y
# sed -i "s/CONFIG_MEMORY_HOTPLUG=y/CONFIG_MEMORY_HOTPLUG=m/g" .config
# sed -i "s/CONFIG_TCP_CONG_DCTCP=y/CONFIG_TCP_CONG_DCTCP=m/g" .config
# egrep "CONFIG_MEMORY_HOTPLUG|CONFIG_TCP_CONG_DCTCP" .config
CONFIG_MEMORY_HOTPLUG=m
CONFIG_TCP_CONG_DCTCP=m
# make olddefconfig
# egrep "CONFIG_MEMORY_HOTPLUG|CONFIG_TCP_CONG_DCTCP" .config
# CONFIG_MEMORY_HOTPLUG is not set
CONFIG_TCP_CONG_DCTCP=m