lkml.org 
[lkml]   [2009]   [Oct]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[patch 2/3] x86_64, ftrace: make ftrace use kernel identity mapping to modify code
On x86_64, kernel text mappings are mapped read-only with CONFIG_DEBUG_RODATA.
So use the kernel identity mapping instead of the kernel text mapping to modify
the kernel text.

Acked-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
---
arch/x86/kernel/ftrace.c | 17 +++++++++++++++++
arch/x86/mm/pageattr.c | 3 +--
2 files changed, 18 insertions(+), 2 deletions(-)

Index: tip/arch/x86/kernel/ftrace.c
===================================================================
--- tip.orig/arch/x86/kernel/ftrace.c
+++ tip/arch/x86/kernel/ftrace.c
@@ -189,9 +189,26 @@ static void wait_for_nmi(void)
nmi_wait_count++;
}

+static inline int
+within(unsigned long addr, unsigned long start, unsigned long end)
+{
+ return addr >= start && addr < end;
+}
+
static int
do_ftrace_mod_code(unsigned long ip, void *new_code)
{
+ /*
+ * On x86_64, kernel text mappings are mapped read-only with
+ * CONFIG_DEBUG_RODATA. So we use the kernel identity mapping instead
+ * of the kernel text mapping to modify the kernel text.
+ *
+ * For 32bit kernels, these mappings are same and we can use
+ * kernel identity mapping to modify code.
+ */
+ if (within(ip, (unsigned long)_text, (unsigned long)_etext))
+ ip = (unsigned long)__va(__pa(ip));
+
mod_code_ip = (void *)ip;
mod_code_newcode = new_code;

Index: tip/arch/x86/mm/pageattr.c
===================================================================
--- tip.orig/arch/x86/mm/pageattr.c
+++ tip/arch/x86/mm/pageattr.c
@@ -279,8 +279,7 @@ static inline pgprot_t static_protection
__pa((unsigned long)__end_rodata) >> PAGE_SHIFT))
pgprot_val(forbidden) |= _PAGE_RW;

-#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA) && \
- !defined(CONFIG_DYNAMIC_FTRACE)
+#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
/*
* Once the kernel maps the text as RO (kernel_set_to_readonly is set),
* kernel text mappings for the large page aligned text, rodata sections



\
 
 \ /
  Last update: 2009-10-29 02:55    [W:1.213 / U:0.944 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site