Feather-Trace: make x86 rewriting impl work despite RO text

Mirror what ftrace does to ensure that we can patch up the text
segment.

1 files changed, 57 insertions, 5 deletions

diff --git a/arch/x86/kernel/ft_event.c b/arch/x86/kernel/ft_event.c
index 37cc33252713..7aa3d0592ff2 100644
--- a/arch/x86/kernel/ft_event.c
+++ b/arch/x86/kernel/ft_event.c
@@ -1,4 +1,7 @@
 #include <linux/types.h>
+#include <linux/module.h>
+#include <asm/cacheflush.h>
+#include <asm/sections.h>
 
 #include <litmus/feather_trace.h>
 
@@ -6,7 +9,7 @@
  * exclusive access to the event table
  */
 
-#ifndef CONFIG_DEBUG_RODATA
+#ifndef CONFIG_RELOCATABLE
 
 #define BYTE_JUMP      0xeb
 #define BYTE_JUMP_LEN  0x02
@@ -22,6 +25,31 @@ struct trace_event {
 extern struct trace_event  __start___event_table[];
 extern struct trace_event  __stop___event_table[];
 
+
+/* NOTE: The following two functions have been stolen from ftrace.c */
+
+static inline int
+within(unsigned long addr, unsigned long start, unsigned long end)
+{
+        return addr >= start && addr < end;
+}
+
+static unsigned long text_ip_addr(unsigned long ip)
+{
+        /*
+         * On x86_64, kernel text mappings are mapped read-only, 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_symbol(ip));
+
+        return ip;
+}
+
 /* Workaround: if no events are defined, then the event_table section does not
  * exist and the above references cause linker errors. This could probably be
  * fixed by adjusting the linker script, but it is easier to maintain for us if
@@ -36,12 +64,17 @@ int ft_enable_event(unsigned long id)
         char* delta;
         unsigned char* instr;
 
+        set_kernel_text_rw();
+        set_all_modules_text_rw();
+
         while (te < __stop___event_table) {
                 if (te->id == id && ++te->count == 1) {
                         instr  = (unsigned char*) te->start_addr;
                         /* make sure we don't clobber something wrong */
                         if (*instr == BYTE_JUMP) {
-                                delta  = (((unsigned char*) te->start_addr) + 1);
+                                delta  = (unsigned char*) text_ip_addr(
+                                                ((unsigned long) te->start_addr)
+                                                + 1);
                                 *delta = 0;
                         }
                 }
@@ -50,6 +83,9 @@ int ft_enable_event(unsigned long id)
                 te++;
         }
 
+        set_all_modules_text_ro();
+        set_kernel_text_ro();
+
         printk(KERN_DEBUG "ft_enable_event: enabled %d events\n", count);
         return count;
 }
@@ -61,11 +97,16 @@ int ft_disable_event(unsigned long id)
         char* delta;
         unsigned char* instr;
 
+        set_kernel_text_rw();
+        set_all_modules_text_rw();
+
         while (te < __stop___event_table) {
                 if (te->id == id && --te->count == 0) {
                         instr  = (unsigned char*) te->start_addr;
                         if (*instr == BYTE_JUMP) {
-                                delta  = (((unsigned char*) te->start_addr) + 1);
+                                delta  = (unsigned char*) text_ip_addr(
+                                                ((unsigned long) te->start_addr)
+                                                + 1);
                                 *delta = te->end_addr - te->start_addr -
                                         BYTE_JUMP_LEN;
                         }
@@ -75,6 +116,9 @@ int ft_disable_event(unsigned long id)
                 te++;
         }
 
+        set_all_modules_text_ro();
+        set_kernel_text_ro();
+
         printk(KERN_DEBUG "ft_disable_event: disabled %d events\n", count);
         return count;
 }
@@ -86,12 +130,16 @@ int ft_disable_all_events(void)
         char* delta;
         unsigned char* instr;
 
+        set_kernel_text_rw();
+        set_all_modules_text_rw();
+
         while (te < __stop___event_table) {
                 if (te->count) {
                         instr  = (unsigned char*) te->start_addr;
                         if (*instr == BYTE_JUMP) {
-                                delta  = (((unsigned char*) te->start_addr)
-                                          + 1);
+                                delta  = (unsigned char*) text_ip_addr(
+                                                ((unsigned long) te->start_addr)
+                                                + 1);
                                 *delta = te->end_addr - te->start_addr -
                                         BYTE_JUMP_LEN;
                                 te->count = 0;
@@ -100,6 +148,10 @@ int ft_disable_all_events(void)
                 }
                 te++;
         }
+
+        set_all_modules_text_ro();
+        set_kernel_text_ro();
+
         return count;
 }