This suggestion looks more like a workaround to get rid of a bigger
issue.
If we do that, we have to use CONFIG_* exclusivity for either
(ro-data protection) or (paravirt, kprobes, immediate values).
One big advantage of my patch is that we can remove weird exclusivity
cases involving paravirt and cpu hotplug, like this one:
-#ifndef CONFIG_KPROBES
-#ifdef CONFIG_HOTPLUG_CPU
- /* It must still be possible to apply SMP alternatives. */
- if (num_possible_cpus() <= 1)
-#endif
- {
- change_page_attr(virt_to_page(start),
- size >> PAGE_SHIFT, PAGE_KERNEL_RX);
- printk("Write protecting the kernel text: %luk\n", size >> 10);
- kernel_text_is_ro = 1;
- }
Mathieu
* S. P. Prasanna ([EMAIL PROTECTED]) wrote:
> On Tue, Jul 03, 2007 at 12:38:22PM -0400, Mathieu Desnoyers wrote:
> > Kprobes can use the text edit lock to insure mutual exclusion when edition
> > the
> > code and make sure the pages are writable.
>
> Linus suggested for splitting ro-data and ro-text; And allow ro-text
> only if kprobes is not configured.
> Please see the discussion thread, URL given below
> http://lkml.org/lkml/2007/6/20/436
>
> This patch below allows to configure and mark the kernel text and
> kernel data as read-only separately. Also kernel text
> is configured read-only if kprobes is not configured.
>
> Thanks
> Prasanna
>
> This patch allows to configure and mark the kernel text and
> kernel data as read-only separately.
>
> Signed-off-by: Prasanna S P. <[EMAIL PROTECTED]>
>
>
> arch/i386/Kconfig.debug | 8 ++++++++
> arch/i386/mm/init.c | 22 ++++++++++++++++------
> 2 files changed, 24 insertions(+), 6 deletions(-)
>
> diff -puN arch/i386/Kconfig.debug~mark-kernel-text-data-ro-seperately-i386
> arch/i386/Kconfig.debug
> ---
> linux-2.6.22-rc6/arch/i386/Kconfig.debug~mark-kernel-text-data-ro-seperately-i386
> 2007-07-04 13:45:24.000000000 +0530
> +++ linux-2.6.22-rc6-prasanna/arch/i386/Kconfig.debug 2007-07-04
> 13:52:31.000000000 +0530
> @@ -56,6 +56,14 @@ config DEBUG_RODATA
> portion of the kernel code won't be covered by a 2MB TLB anymore.
> If in doubt, say "N".
>
> +config DEBUG_ROTEXT
> + bool "Write protect kernel text"
> + depends on DEBUG_RODATA && !KPROBES
> + help
> + Mark the kernel text as write-protected in the pagetables.
> + Only allow this if kprobes is not configured.
> + If in doubt, say "N".
> +
> config 4KSTACKS
> bool "Use 4Kb for kernel stacks instead of 8Kb"
> depends on DEBUG_KERNEL
> diff -puN arch/i386/mm/init.c~mark-kernel-text-data-ro-seperately-i386
> arch/i386/mm/init.c
> ---
> linux-2.6.22-rc6/arch/i386/mm/init.c~mark-kernel-text-data-ro-seperately-i386
> 2007-07-04 13:45:24.000000000 +0530
> +++ linux-2.6.22-rc6-prasanna/arch/i386/mm/init.c 2007-07-04
> 13:51:39.000000000 +0530
> @@ -792,14 +792,11 @@ static int noinline do_test_wp_bit(void)
> return flag;
> }
>
> -#ifdef CONFIG_DEBUG_RODATA
> -
> -void mark_rodata_ro(void)
> +static inline void mark_rwtext_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)
> @@ -809,9 +806,22 @@ void mark_rodata_ro(void)
> size >> PAGE_SHIFT, PAGE_KERNEL_RX);
> printk("Write protecting the kernel text: %luk\n", size >> 10);
> }
> +
> + /*
> + * global_flush_tlb() will be called after marking the data as readonly.
> + */
> +}
> +
> +#ifdef CONFIG_DEBUG_RODATA
> +
> +void mark_rodata_ro(void)
> +{
> + unsigned long start = PFN_ALIGN(_etext);
> + unsigned long size = (unsigned long)__end_rodata - start;
> +
> +#ifdef CONFIG_DEBUG_ROTEXT
> + mark_rwtext_ro();
> #endif
> - start += size;
> - size = (unsigned long)__end_rodata - start;
> change_page_attr(virt_to_page(start),
> size >> PAGE_SHIFT, PAGE_KERNEL_RO);
> printk("Write protecting the kernel read-only data: %luk\n",
>
> _
> --
> Prasanna S.P.
> Linux Technology Center
> India Software Labs, IBM Bangalore
> Email: [EMAIL PROTECTED]
> Ph: 91-80-41776329
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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