Re: [PATCH v2 3/5] x86/alternative: exclude text poking against change_page_attr()

[Jiri Slaby]

On 13. 08. 26, 11:01, Mike Rapoport wrote:
> From: Pedro Falcato <pfalcato@xxxxxxx>
>
>  From time to time, the following BUG can be observed[0]:
>
> > kernel BUG at arch/x86/kernel/alternative.c:2576!
> > Oops: invalid opcode: 0000 [#1] SMP NOPTI
> > CPU: 0 UID: 0 PID: 355 Comm: (udev-worker) Not tainted 7.1.3-1-default #1 PREEMPT(full) openSUSE Tumbleweed  8c1795b03ec64f997e57a8ad38b1161e3b98da64
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS unknown 02/02/2022
> > RIP: 0010:__text_poke+0x2aa/0x450
> > Call Trace:
> >   <TASK>
> >   smp_text_poke_batch_finish+0x2a7/0x320
> >   __static_call_transform+0xb7/0x220
> >   arch_static_call_transform+0x5b/0xb0
> >   __static_call_init+0xe9/0x270
> >   static_call_module_notify+0x11f/0x150
> >   notifier_call_chain+0x61/0xe0
> >   blocking_notifier_call_chain_robust+0x63/0xc0
> >   load_module+0x1c92/0x20c0
> >   init_module_from_file+0xd8/0x140
> >   idempotent_init_module+0x100/0x2f0
> >   __x64_sys_finit_module+0x71/0xe0
> >   do_syscall_64+0xe1/0x610
> >   entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> which matches the following BUG_ON in alternative.c:
> 	/*
> 	 * If something went wrong, crash and burn since recovery paths are not
> 	 * implemented.
> 	 */
> 	BUG_ON(!pages[0] || (cross_page_boundary && !pages[1]));
>
> This can happen if vmalloc_to_page() fails, for any reason. Such can happen
> if text poking races with CPA, which can possibly result in the collapsing
> of page tables (or breaking of PMD hugepages). It is not a problem for most
> users of vmalloc_to_page() (they solely own the vmalloc'd range) but, when
> CONFIG_ARCH_HAS_EXECMEM_ROX=y, various modules own a single execmem vmalloc
> range, and can call set_memory_*() in parallel on it. This can happen to
> race against __text_poke and cause havoc in vmalloc_to_page().
>
> Fix it by excluding against CPA using the init_mm mmap read lock.
>
> Fixes: 64f6a4e10c05 ("x86: re-enable EXECMEM_ROX support")
> Reported-by: Jiri Slaby <jirislaby@xxxxxxxxxx>

FWIW
Tested-by: Jiri Slaby <jirislaby@xxxxxxxxxx>

We have not seen any BUGs since applied to the SUSE's kernel.
https://bugzilla.suse.com/show_bug.cgi?id=1271202#c26

thanks,
--
js
suse labs