Re: [syzbot] WARNING in __change_page_attr_set_clr

[Dave Hansen]

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.