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Date:   Sun, 25 Sep 2022 09:44:45 -0700
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Subject: Re: [syzbot] WARNING in __change_page_attr_set_clr
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To:     syzbot <syzbot+cdcd5043ce8155d92ab1@syzkaller.appspotmail.com>,
        bp@alien8.de, brijesh.singh@amd.com, dan.j.williams@intel.com,
        dave.hansen@linux.intel.com, hpa@zytor.com, jane.chu@oracle.com,
        kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org,
        luto@kernel.org, mingo@redhat.com, peterz@infradead.org,
        seanjc@google.com, syzkaller-bugs@googlegroups.com,
        tglx@linutronix.de, thomas.lendacky@amd.com, x86@kernel.org,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        John Fastabend <john.fastabend@gmail.com>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <bpf@vger.kernel.org>
References: <00000000000076f3a305e97e9229@google.com>
From:   Dave Hansen <dave.hansen@intel.com>
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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.