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

Arjan van de Ven
2007-06-21T05:27:20Z

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.

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;

--
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