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

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Date:   Mon, 26 Sep 2022 09:28:43 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        tech-board@...ts.linuxfoundation.org,
        Song Liu <songliubraving@...com>,
        Kernel Team <Kernel-team@...com>, jane.chu@...cle.com,
        Tom Lendacky <thomas.lendacky@....com>,
        X86 ML <x86@...nel.org>, brijesh.singh@....com,
        "open list:BPF \(Safe dynamic programs and tools\)" 
        <bpf@...r.kernel.org>, Daniel Borkmann <daniel@...earbox.net>,
        Peter Zijlstra <peterz@...radead.org>, seanjc@...gle.com,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        John Fastabend <john.fastabend@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [Tech-board] [syzbot] WARNING in __change_page_attr_set_clr

On Sun, 25 Sep 2022 14:55:46 -0700
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> On Sun, Sep 25, 2022 at 9:44 AM Dave Hansen <dave.hansen@...el.com> wrote:
> >
> > On 9/25/22 04:18, syzbot wrote:  
> > > ------------[ cut here ]------------
> > > CPA refuse W^X violation: 8000000000000163 -> 0000000000000163 range: 0xffffffffa0401000 - 0xffffffffa0401fff PFN 7d8d5
> > > WARNING: CPU: 0 PID: 3607 at arch/x86/mm/pat/set_memory.c:600 verify_rwx arch/x86/mm/pat/set_memory.c:600 [inline]
> > > WARNING: CPU: 0 PID: 3607 at arch/x86/mm/pat/set_memory.c:600 __change_page_attr arch/x86/mm/pat/set_memory.c:1569 [inline]
> > > WARNING: CPU: 0 PID: 3607 at arch/x86/mm/pat/set_memory.c:600 __change_page_attr_set_clr+0x1f40/0x2020 arch/x86/mm/pat/set_memory.c:1691
> > > Modules linked in:  
> >
> > Yay, one of these that isn't due to wonky 32-bit kernels!
> >
> > This one looks to be naughty intentionally:
> >  
> > > void *bpf_jit_alloc_exec_page(void)
> > > {  
> > ...  
> > >         /* Keep image as writeable. The alternative is to keep flipping ro/rw
> > >          * every time new program is attached or detached.
> > >          */
> > >         set_memory_x((long)image, 1);
> > >         return image;
> > > }  
> >
> > For STRICT_KERNEL_RWX kernels, I think we would really rather that this
> > code *did* flip ro/rw every time a new BPF program is attached or detached.  
> 
> Steven Rostedt noticed that comment around the middle of August
> and told you and Peter about it.
> Then Peter added a WARN_ONCE in commit
> https://lore.kernel.org/all/YwySW3ROc21hN7g9@hirez.programming.kicks-ass.net/
> to explicitly trigger that known issue.
> Sure enough the fedora fails to boot on linux-next since then,
> because systemd is loading bpf programs that use bpf trampoline.
> The boot issue was was reported 3 days ago:
> https://lore.kernel.org/bpf/c84cc27c1a5031a003039748c3c099732a718aec.camel@kernel.org/T/#u
> Now we're trying to urgently address it with:
> https://lore.kernel.org/bpf/20220923211837.3044723-1-song@kernel.org/
> 
> So instead of pinging us with your w^x concern you've decided
> to fail hard in -next to force the issue and
> now acting like this is something surprising to you?!
> 
> This is Code of Conduct "worthy" behavior demonstrated

Here's the link to the Code of Conduct:

https://www.kernel.org/doc/html/latest/process/code-of-conduct.html

Which states:

  Examples of behavior that contributes to creating a positive environment include:

    - Using welcoming and inclusive language
    - Being respectful of differing viewpoints and experiences
    - Gracefully accepting constructive criticism
    - Focusing on what is best for the community
    - Showing empathy towards other community members

  Examples of unacceptable behavior by participants include:

    - The use of sexualized language or imagery and unwelcome sexual attention or advances
    - Trolling, insulting/derogatory comments, and personal or political attacks
    - Public or private harassment
    - Publishing others’ private information, such as a physical or electronic address, without explicit permission
    - Other conduct which could reasonably be considered inappropriate in a professional setting

I do not see how Dave's response is a violation of any of the above.


> by a newly elected member of the Technical Advisory Board.
> Please consider resigning.

Asking someone to resign is a personal attack, and that can be construed as
a violation of the Code of Conduct.

> A TAB member should be better than this.
> 

Let's please keep this on a technical level, as there appears to be a fix
we all can agree on, and let's move forward on that.

Thanks,

-- Steve