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Subject[PATCH] Text Edit Lock - i386 Use kernel_text_is_ro
Text Edit Lock - i386 use kernel_text_is_ro

* Christoph Hellwig (hch@infradead.org) wrote:
> On Fri, Jul 13, 2007 at 09:21:36PM -0400, Mathieu Desnoyers wrote:
> > +#ifdef CONFIG_DEBUG_RODATA
> > +static int rodata_marked;
> > +#endif
>
> Maybe I'm missing something, but the rodata section should always stay
> r/o, only text needs locking/unlocking, no?
>
> Given that all code in this patch only operates on .text this seems fine,
> but the variables/config options are grossly misnamed then. And actually
> making rodata r/o doesn't seem like a pure debugging thing to me either.

I think it will change to two different config options eventually (RO
data and RO text). But for now, it makes more sense to use the
kernel_text_is_ro variable.

And since we do not plan to call kernel_text_mark_rw()/kernel_text_unmark()
in the middle of mark_rodata_ro (we are still at boot time), there is no
need to wait until after global_flush_tlb() mark the rodata. And it makes to
rename mark_rodata_ro into kernel_rodata_is_ro.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: hch@infradead.org
---
arch/i386/mm/init.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

Index: linux-2.6-lttng/arch/i386/mm/init.c
===================================================================
--- linux-2.6-lttng.orig/arch/i386/mm/init.c 2007-07-14 16:04:20.000000000 -0400
+++ linux-2.6-lttng/arch/i386/mm/init.c 2007-07-14 16:05:45.000000000 -0400
@@ -47,6 +47,7 @@
#include <asm/paravirt.h>

int kernel_text_is_ro;
+int kernel_rodata_is_ro;
unsigned int __VMALLOC_RESERVE = 128 << 20;

DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
@@ -54,9 +55,6 @@ unsigned long highstart_pfn, highend_pfn

static int noinline do_test_wp_bit(void);

-#ifdef CONFIG_DEBUG_RODATA
-static int rodata_marked;
-#endif

/*
* Creates a middle page table and puts a pointer to it in the
@@ -817,6 +815,7 @@ void mark_rodata_ro(void)
size >> PAGE_SHIFT, PAGE_KERNEL_RO);
printk("Write protecting the kernel read-only data: %luk\n",
size >> 10);
+ kernel_rodata_is_ro = 1;

/*
* change_page_attr() requires a global_flush_tlb() call after it.
@@ -825,7 +824,6 @@ void mark_rodata_ro(void)
* of who is the culprit.
*/
global_flush_tlb();
- rodata_marked = 1;
}

/*
@@ -834,7 +832,7 @@ void mark_rodata_ro(void)
*/
void __kprobes kernel_text_mark_rw(unsigned long address, size_t len)
{
- if (rodata_marked && address >= PFN_ALIGN(_text)
+ if (kernel_text_is_ro && address >= PFN_ALIGN(_text)
&& (address + len) <= PFN_ALIGN(_etext)) {
unsigned long nr_pages;
nr_pages = ((address + len) >> PAGE_SHIFT)
@@ -851,7 +849,7 @@ EXPORT_SYMBOL_GPL(kernel_text_mark_rw);

void __kprobes kernel_text_unmark(unsigned long address, size_t len)
{
- if (rodata_marked && address >= PFN_ALIGN(_text)
+ if (kernel_text_is_ro && address >= PFN_ALIGN(_text)
&& (address + len) <= PFN_ALIGN(_etext)) {
unsigned long nr_pages;
nr_pages = ((address + len) >> PAGE_SHIFT)
--
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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