linux-kernel - Re: [PATCH v2] comedi: Flush partial mappings in error case

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAG48ez1RWTEW_ZJBYbt6WWJX90haM61pwqqb3u9Pq8C_q71bQQ@mail.gmail.com>
Date: Thu, 17 Oct 2024 21:07:10 +0200
From: Jann Horn <jannh@...gle.com>
To: Ian Abbott <abbotti@....co.uk>
Cc: kernel test robot <lkp@...el.com>, H Hartley Sweeten <hsweeten@...ionengravers.com>, 
	Frank Mori Hess <fmh6jj@...il.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org
Subject: Re: [PATCH v2] comedi: Flush partial mappings in error case

On Thu, Oct 17, 2024 at 11:48 AM Ian Abbott <abbotti@....co.uk> wrote:
> On 17/10/2024 10:29, Ian Abbott wrote:
> > On 16/10/2024 23:05, Jann Horn wrote:
> >> On Wed, Oct 16, 2024 at 8:05 PM kernel test robot <lkp@...el.com> wrote:
> >>> [auto build test ERROR on 6485cf5ea253d40d507cd71253c9568c5470cd27]
> >>>
> >>> url:    https://github.com/intel-lab-lkp/linux/commits/Jann-Horn/
> >>> comedi-Flush-partial-mappings-in-error-case/20241016-022809
> >>> base:   6485cf5ea253d40d507cd71253c9568c5470cd27
> >>> patch link:    https://lore.kernel.org/r/20241015-comedi-tlb-v2-1-
> >>> cafb0e27dd9a%40google.com
> >>> patch subject: [PATCH v2] comedi: Flush partial mappings in error case
> >>> config: arm-randconfig-004-20241016 (https://download.01.org/0day-ci/
> >>> archive/20241017/202410170111.K30oyTWa-lkp@...el.com/config)
> >>> compiler: arm-linux-gnueabi-gcc (GCC) 14.1.0
> >>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/
> >>> archive/20241017/202410170111.K30oyTWa-lkp@...el.com/reproduce)
> >>>
> >>> If you fix the issue in a separate patch/commit (i.e. not just a new
> >>> version of
> >>> the same patch/commit), kindly add following tags
> >>> | Reported-by: kernel test robot <lkp@...el.com>
> >>> | Closes: https://lore.kernel.org/oe-kbuild-
> >>> all/202410170111.K30oyTWa-lkp@...el.com/
> >>>
> >>> All errors (new ones prefixed by >>):
> >>>
> >>>     arm-linux-gnueabi-ld: drivers/comedi/comedi_fops.o: in function
> >>> `comedi_mmap':
> >>>>> comedi_fops.c:(.text+0x4be): undefined reference to `zap_vma_ptes'
> >>
> >> Ugh, this one is from a nommu build ("# CONFIG_MMU is not set"), it
> >> makes sense that you can't zap PTEs when you don't have any PTEs at
> >> all... what really impresses me about this is that the rest of the
> >> code compiles on nommu. I'm pretty sure this codepath wouldn't
> >> actually _work_ on nommu, but apparently compiling it works?
> >>
> >> I don't know what the right fix is here - should the entire comedi
> >> driver be gated on CONFIG_MMU, or only a subset of the mmap handler,
> >> or something else?
> >
> > Given that it would also affect a lot of fbdev drivers that would also
> > benefit from zapping partial mappings, I suggest that gating on
> > CONFIG_MMU would not be the correct fix.
>
> Perhaps just add an #ifdef CONFIG_MMU around the affected call for now?

Sure, I guess that works, though it's not particularly pretty.
(And this codepath looks like it won't really work on nommu either way...)

I'll change it that way for now.