Re: [1/2] 2.6.22-rc5: known regressions with patches

S. P. Prasanna
2007-06-21T07:11:19Z

On Wed, Jun 20, 2007 at 10:23:21PM -0700, Arjan van de Ven wrote:
> On Wed, 2007-06-20 at 16:50 -0700, Linus Torvalds wrote:
> >
> > On Wed, 20 Jun 2007, Arjan van de Ven wrote:
> > >
> > > the real fix would be something like this instead:
> >
> > If people can test this, and confirm it works, please send a patch that
> > not only does this ad undoes the Kconfig language. It looks like the
> > right thing to do, but I won't touch it without somebody who actually
> > tested these combinarions sending in a patch.
>
> Hi,
>
> I have tested this on x86_64, and without the config language, the
> original oopses, while with the patch below it works fine (as expected).
> I've not been able to test the i386 one (no 32 bit testboxes since 2
> years) but the change is even simpler there, just an ifdef around the
> entire kernel text marking.

I tested this patch on i386 box, it seems to work fine.

Thanks
Prasanna
>
>
>
> Do not mark the kernel text read only if KPROBES is in the kernel;
> kprobes needs to hot-patch the kernel text to insert it's
> instrumentation. In this case, only mark the .rodata segment as read
> only.
>
> Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
>
> --- linux-2.6.22-rc5/arch/i386/Kconfig.debug.org 2007-06-20 22:20:30.000000000 -0700
> +++ linux-2.6.22-rc5/arch/i386/Kconfig.debug 2007-06-20 22:20:55.000000000 -0700
> @@ -49,7 +49,6 @@ config DEBUG_PAGEALLOC
> config DEBUG_RODATA
> bool "Write protect kernel read-only data structures"
> depends on DEBUG_KERNEL
> - depends on !KPROBES # temporary for 2.6.22
> help
> Mark the kernel read-only data as write-protected in the pagetables,
> in order to catch accidental (and incorrect) writes to such const
> --- linux-2.6.22-rc5/arch/x86_64/Kconfig.debug.org 2007-06-20 22:20:28.000000000 -0700
> +++ linux-2.6.22-rc5/arch/x86_64/Kconfig.debug 2007-06-20 22:20:44.000000000 -0700
> @@ -9,7 +9,6 @@ source "lib/Kconfig.debug"
> config DEBUG_RODATA
> bool "Write protect kernel read-only data structures"
> depends on DEBUG_KERNEL
> - depends on !KPROBES # temporary for 2.6.22
> help
> Mark the kernel read-only data as write-protected in the pagetables,
> in order to catch accidental (and incorrect) writes to such const data.
> --- linux-2.6.22-rc5/arch/i386/mm/init.c.org 2007-06-20 22:18:40.000000000 -0700
> +++ linux-2.6.22-rc5/arch/i386/mm/init.c 2007-06-20 22:19:45.000000000 -0700
> @@ -799,6 +799,7 @@ void mark_rodata_ro(void)
> unsigned long start = PFN_ALIGN(_text);
> unsigned long size = PFN_ALIGN(_etext) - start;
>
> +#ifndef CONFIG_KPROBES
> #ifdef CONFIG_HOTPLUG_CPU
> /* It must still be possible to apply SMP alternatives. */
> if (num_possible_cpus() <= 1)
> @@ -808,7 +809,7 @@ void mark_rodata_ro(void)
> size >> PAGE_SHIFT, PAGE_KERNEL_RX);
> printk("Write protecting the kernel text: %luk\n", size >> 10);
> }
> -
> +#endif
> start += size;
> size = (unsigned long)__end_rodata - start;
> change_page_attr(virt_to_page(start),
> --- linux-2.6.22-rc5/arch/x86_64/mm/init.c.org 2007-06-20 21:44:15.000000000 -0700
> +++ linux-2.6.22-rc5/arch/x86_64/mm/init.c 2007-06-20 22:17:45.000000000 -0700
> @@ -605,6 +605,11 @@ void mark_rodata_ro(void)
> if (num_possible_cpus() > 1)
> start = (unsigned long)_etext;
> #endif
> +
> +#ifdef CONFIG_KPROBES
> + start = (unsigned long)__start_rodata;
> +#endif
> +
> end = (unsigned long)__end_rodata;
> start = (start + PAGE_SIZE - 1) & PAGE_MASK;
> end &= PAGE_MASK;
>
> --
> if you want to mail me at work (you don't), use arjan (at) linux.intel.com
> Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

--
Thanks & Regards
Prasanna S.P.
Linux Technology Center
India Software Labs, IBM Bangalore
Email: prasanna@in.ibm.com
Ph: 91-80-41776329