Re: [syzbot] WARNING in __change_page_attr_set_clr

[Randy Dunlap]

On 9/25/22 14:55, Alexei Starovoitov wrote:
> On Sun, Sep 25, 2022 at 9:44 AM Dave Hansen <dave.hansen@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> 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@xxxxxxxxxx/T/#u
> Now we're trying to urgently address it with:
> https://lore.kernel.org/bpf/20220923211837.3044723-1-song@xxxxxxxxxx/
> 
> 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
> by a newly elected member of the Technical Advisory Board.
> Please consider resigning.
> A TAB member should be better than this.

If it is (and I don't see it), just file a complaint.
Don't try to be the enforcer.

-- 
~Randy