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Subject[tip:x86/mm] x86_64, ftrace: Make ftrace use kernel identity mapping to modify code
Commit-ID:  55ca3cc1746335bb6ef1d3894ddb6d0c729b3518
Gitweb: http://git.kernel.org/tip/55ca3cc1746335bb6ef1d3894ddb6d0c729b3518
Author: Suresh Siddha <suresh.b.siddha@intel.com>
AuthorDate: Wed, 28 Oct 2009 18:46:57 -0800
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Mon, 2 Nov 2009 17:16:36 +0100

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.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20091029024821.080941108@sbs-t61.sc.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
arch/x86/kernel/ftrace.c | 17 +++++++++++++++++
arch/x86/mm/pageattr.c | 3 +--
2 files changed, 18 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 9dbb527..944e982 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -187,9 +187,26 @@ 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;

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 8d1e8d9..09a140c 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -279,8 +279,7 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
__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

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