linux-kernel - Re: [syzbot] WARNING in __change_page_attr_set

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Message-ID: <a2673df8-cf8a-b94a-68cd-1e2777fb5cf4@intel.com>
Date:   Sun, 25 Sep 2022 17:10:19 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        tech-board@...ts.linuxfoundation.org,
        Song Liu <songliubraving@...com>,
        Kernel Team <Kernel-team@...com>
Cc:     Borislav Petkov <bp@...en8.de>, brijesh.singh@....com,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, jane.chu@...cle.com,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, seanjc@...gle.com,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <bpf@...r.kernel.org>
Subject: Re: [syzbot] WARNING in __change_page_attr_set_clr

On 9/25/22 14:55, Alexei Starovoitov wrote:
> And, sorry, "flip ro/rw every time" is not a good idea from
> security pov.
> There is a much better solution that stalled on the code review.
> In the meantime we'll land a quick fix to re-enable boot in -next
> in the coming days.

Peter, I remember an earlier version of your patch having some various
enforcement modes.  Since the strict enforcement has actually broken a
few things, should we resurrect the nicer soft detection mode?  Or,
maybe make the soft one the only mode for now?

Alexei, the "quick fix" looks sane to me at first glance.  Is there
something in there that's not viable long-term?

Also, the intention here was not to force any issues.  I thought the
earlier discussion resulted in a bpf fix and applying Peter's patch was
intended to catch _future_ issues.  I should have double-checked before
applying it.  My apologies.