From: Dmitry Vyukov <dvyukov@google.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Dan Carpenter <dan.carpenter@oracle.com>,
Paolo Bonzini <pbonzini@redhat.com>,
syzbot <syzbot+015dd7cdbbbc2c180c65@syzkaller.appspotmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Borislav Petkov <bp@alien8.de>,
Daniel Vetter <daniel.vetter@ffwll.ch>,
daniel.vetter@intel.com, "H. Peter Anvin" <hpa@zytor.com>,
Jim Mattson <jmattson@google.com>,
James Morris <jmorris@namei.org>, Joerg Roedel <joro@8bytes.org>,
KVM list <kvm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux Media Mailing List <linux-media@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
linux-security-module <linux-security-module@vger.kernel.org>,
m.szyprowski@samsung.com,
Mauro Carvalho Chehab <mchehab@kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Sean Christopherson <seanjc@google.com>,
"Serge E. Hallyn" <serge@hallyn.com>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Tomasz Figa <tfiga@chromium.org>,
Thomas Gleixner <tglx@linutronix.de>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
"the arch/x86 maintainers" <x86@kernel.org>
Subject: Re: [syzbot] WARNING in unsafe_follow_pfn
Date: Tue, 13 Apr 2021 20:27:57 +0200 [thread overview]
Message-ID: <CACT4Y+b6g7DNQTRo0VSFgPzAZF2vMJOcnijuLWeLxUtOWL1nrA@mail.gmail.com> (raw)
In-Reply-To: <20210413181145.GK227011@ziepe.ca>
On Tue, Apr 13, 2021 at 8:11 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> On Tue, Apr 13, 2021 at 07:20:12PM +0200, Dmitry Vyukov wrote:
> > > > Plus users are going to be seeing this as well. According to the commit
> > > > message for 69bacee7f9ad ("mm: Add unsafe_follow_pfn") "Unfortunately
> > > > there's some users where this is not fixable (like v4l userptr of iomem
> > > > mappings)". It sort of seems crazy to dump this giant splat and then
> > > > tell users to ignore it forever because it can't be fixed... 0_0
> > >
> > > I think the discussion conclusion was that this interface should not
> > > be used by userspace anymore, it is obsolete by some new interface?
> > >
> > > It should be protected by some kconfig and the kconfig should be
> > > turned off for syzkaller runs.
> >
> > If this is not a kernel bug, then it must not use WARN_ON[_ONCE]. It
> > makes the kernel untestable for both automated systems and humans:
>
> It is a kernel security bug triggerable by userspace.
>
> > And if it's a kernel bug reachable from user-space, then I think this
> > code should be removed entirely, not just on all testing systems. Or
> > otherwise if we are not removing it for some reason, then it needs to
> > be fixed.
>
> Legacy embedded systems apparently require it.
>
> It should be blocked by a kconfig. Distributions and syzkaller runs
> should not enable that kconfig. What else can we do for insane uapi?
I see. Adding a config gives at least some path forward, so if there
are no better options, that's do that. If we default it to 'n' and add
a bold warning in the description, it may work.
next prev parent reply other threads:[~2021-04-13 18:28 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-30 15:26 [syzbot] WARNING in unsafe_follow_pfn syzbot
2021-03-30 17:04 ` Paolo Bonzini
2021-03-31 4:29 ` Dan Carpenter
2021-04-01 12:19 ` Jason Gunthorpe
2021-04-13 17:20 ` Dmitry Vyukov
2021-04-13 18:11 ` Jason Gunthorpe
2021-04-13 18:27 ` Dmitry Vyukov [this message]
2021-04-14 4:37 ` Dan Carpenter
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