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Date: Thu, 7 Jun 2007 09:54:21 +0530
From: "S. P. Prasanna" <prasanna@...ibm.com>
To: Ian McDonald <ian.mcdonald@...di.co.nz>,
Andrew Morton <akpm@...ux-foundation.org>,
Andi Kleen <ak@...e.de>
Cc: Jim Keniston <jkenisto@...ibm.com>,
Chuck Ebbert <cebbert@...hat.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
ananth@...ibm.com, anil.s.keshavamurthy@...el.com,
"David S. Miller" <davem@...emloft.net>,
Patrick Andrieux <patrick.andrieux@...il.com>,
DCCP Mailing List <dccp@...r.kernel.org>,
jbeulich@...ell.com, systemtap@...rces.redhat.com
Subject: Re: [PATCH] Kprobes x86_64 fix for mark ro data
This patch fixes the problem of page protection introduced by
CONFIG_DEBUG_RODATA for x86_64 architecture. As per Andi
Kleen's suggestion, the kernel text pages are marked writeable
only for a short duration to insert or remove the breakpoints.
Signed-off-by: Prasanna S P<prasanna@...ibm.com>
Ack-ed-by: Jim Keniston <jkenisto@...ibm.com>
arch/x86_64/kernel/kprobes.c | 26 ++++++++++++++++++++++++++
arch/x86_64/mm/init.c | 6 +++++-
include/asm-x86_64/kprobes.h | 10 ++++++++++
3 files changed, 41 insertions(+), 1 deletion(-)
diff -puN arch/x86_64/kernel/kprobes.c~kprobes-mark-ro-data-fix-x86_64 arch/x86_64/kernel/kprobes.c
--- linux-2.6.22-rc2/arch/x86_64/kernel/kprobes.c~kprobes-mark-ro-data-fix-x86_64 2007-06-07 09:20:33.000000000 +0530
+++ linux-2.6.22-rc2-prasanna/arch/x86_64/kernel/kprobes.c 2007-06-07 09:20:33.000000000 +0530
@@ -209,16 +209,42 @@ static void __kprobes arch_copy_kprobe(s
void __kprobes arch_arm_kprobe(struct kprobe *p)
{
+ unsigned long addr = (unsigned long)p->addr;
+ int page_readonly = 0;
+
+ if (kernel_readonly_text(addr)) {
+ change_page_attr_addr(addr, 1, PAGE_KERNEL_EXEC);
+ global_flush_tlb();
+ page_readonly = 1;
+ }
*p->addr = BREAKPOINT_INSTRUCTION;
flush_icache_range((unsigned long) p->addr,
(unsigned long) p->addr + sizeof(kprobe_opcode_t));
+ if (page_readonly) {
+ change_page_attr_addr(addr, 1, PAGE_KERNEL_RO);
+ global_flush_tlb();
+ }
}
void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
+ unsigned long addr = (unsigned long)p->addr;
+ int page_readonly = 0;
+
+ if (kernel_readonly_text(addr)) {
+ change_page_attr_addr(addr, 1, PAGE_KERNEL_EXEC);
+ global_flush_tlb();
+ page_readonly = 1;
+ }
+
*p->addr = p->opcode;
flush_icache_range((unsigned long) p->addr,
(unsigned long) p->addr + sizeof(kprobe_opcode_t));
+
+ if (page_readonly) {
+ change_page_attr_addr(addr, 1, PAGE_KERNEL_RO);
+ global_flush_tlb();
+ }
}
void __kprobes arch_remove_kprobe(struct kprobe *p)
diff -puN include/asm-x86_64/kprobes.h~kprobes-mark-ro-data-fix-x86_64 include/asm-x86_64/kprobes.h
--- linux-2.6.22-rc2/include/asm-x86_64/kprobes.h~kprobes-mark-ro-data-fix-x86_64 2007-06-07 09:20:33.000000000 +0530
+++ linux-2.6.22-rc2-prasanna/include/asm-x86_64/kprobes.h 2007-06-07 09:20:33.000000000 +0530
@@ -26,6 +26,7 @@
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/percpu.h>
+#include <asm-generic/sections.h>
#define __ARCH_WANT_KPROBES_INSN_SLOT
@@ -88,4 +89,13 @@ extern int kprobe_handler(struct pt_regs
extern int kprobe_exceptions_notify(struct notifier_block *self,
unsigned long val, void *data);
+extern int kernel_text_is_ro;
+static inline int kernel_readonly_text(unsigned long address)
+{
+ if (kernel_text_is_ro && ((address >= (unsigned long)_stext)
+ && (address < (unsigned long) _etext)))
+ return 1;
+
+ return 0;
+}
#endif /* _ASM_KPROBES_H */
diff -puN arch/x86_64/mm/init.c~kprobes-mark-ro-data-fix-x86_64 arch/x86_64/mm/init.c
--- linux-2.6.22-rc2/arch/x86_64/mm/init.c~kprobes-mark-ro-data-fix-x86_64 2007-06-07 09:20:33.000000000 +0530
+++ linux-2.6.22-rc2-prasanna/arch/x86_64/mm/init.c 2007-06-07 09:20:33.000000000 +0530
@@ -48,6 +48,7 @@
#define Dprintk(x...)
#endif
+int kernel_text_is_ro;
const struct dma_mapping_ops* dma_ops;
EXPORT_SYMBOL(dma_ops);
@@ -598,10 +599,13 @@ void mark_rodata_ro(void)
{
unsigned long start = (unsigned long)_stext, end;
+ kernel_text_is_ro = 1;
#ifdef CONFIG_HOTPLUG_CPU
/* It must still be possible to apply SMP alternatives. */
- if (num_possible_cpus() > 1)
+ if (num_possible_cpus() > 1) {
start = (unsigned long)_etext;
+ kernel_text_is_ro = 0;
+ }
#endif
end = (unsigned long)__end_rodata;
start = (start + PAGE_SIZE - 1) & PAGE_MASK;
_
--
Prasanna S.P.
Linux Technology Center
India Software Labs, IBM Bangalore
Email: prasanna@...ibm.com
Ph: 91-80-41776329
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