Re: [BUGFIX PATCH] x86: Fix fixmap page order for FIX_TEXT_POKE0,1

Masami Hiramatsu
2009-07-01T22:09:17Z

Mathieu Desnoyers wrote:
> Masami wrote :
>
>> Since the fixmap pages are assigned higher address to lower, text_poke()
>> has to use it with inverted order (FIX_TEXT_POKE1 to FIX_TEXT_POKE0).
>
> I prefer to just invert the order of the fixmap declaration. It's simpler and
> more straightforward.

It's ok for me too.

> Backward fixmaps seems to be used by both x86 32 and 64.
>
> It's a really nasty bug, because it only hurts when instructions to patch are
> crossing a page boundary. If this happens, the fixmap write accesses
> will spill on the following fixmap, which may very well crash the
> system. And this does not crash the system, it could leave illegal
> instructions in place. Thanks Masami for finding this.
>
> It seems to have crept into the 2.6.30-rc series, so this calls for a
> -stable inclusion.

Right, thanks.

>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>

Acked-by: Masami Hiramatsu <mhiramat@redhat.com>

> Cc: Ingo Molnar <mingo@elte.hu>
> CC: stable@kernel.org
> ---
> arch/x86/include/asm/fixmap.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> Index: linux-2.6-lttng/arch/x86/include/asm/fixmap.h
> ===================================================================
> --- linux-2.6-lttng.orig/arch/x86/include/asm/fixmap.h 2009-07-01 16:52:57.000000000 -0400
> +++ linux-2.6-lttng/arch/x86/include/asm/fixmap.h 2009-07-01 16:54:52.000000000 -0400
> @@ -111,8 +111,8 @@ enum fixed_addresses {
> #ifdef CONFIG_PARAVIRT
> FIX_PARAVIRT_BOOTMAP,
> #endif
> - FIX_TEXT_POKE0, /* reserve 2 pages for text_poke() */
> - FIX_TEXT_POKE1,
> + FIX_TEXT_POKE1, /* reserve 2 pages for text_poke() */
> + FIX_TEXT_POKE0, /* first page is last, because allocation is backward */
> __end_of_permanent_fixed_addresses,
> #ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
> FIX_OHCI1394_BASE,
>

--
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com