x86,kgdb: Fix DEBUG_RODATA limitation using text_poke()

There has long been a limitation using software breakpoints with a
kernel compiled with CONFIG_DEBUG_RODATA going back to 2.6.26. For
this particular patch, it will apply cleanly and has been tested all
the way back to 2.6.36.

The kprobes code uses the text_poke() function which accommodates
writing a breakpoint into a read-only page.  The x86 kgdb code can
solve the problem similarly by overriding the default breakpoint
set/remove routines and using text_poke() directly.

The x86 kgdb code will first attempt to use the traditional
probe_kernel_write(), and next try using a the text_poke() function.
The break point install method is tracked such that the correct break
point removal routine will get called later on.

Cc: x86@kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: stable@vger.kernel.org # >= 2.6.36
Inspried-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

1 files changed, 0 insertions, 17 deletions

diff --git a/drivers/misc/kgdbts.c b/drivers/misc/kgdbts.c
index d087456ba089..3aa9a969b373 100644
--- a/drivers/misc/kgdbts.c
+++ b/drivers/misc/kgdbts.c
@@ -968,22 +968,6 @@ static void run_singlestep_break_test(void)
         kgdbts_break_test();
 }
 
-static void test_debug_rodata(void)
-{
-#ifdef CONFIG_DEBUG_RODATA
-        /* Until there is an api to write to read-only text segments, use
-         * HW breakpoints for the remainder of any tests, else print a
-         * failure message if hw breakpoints do not work.
-         */
-        if (!(arch_kgdb_ops.flags & KGDB_HW_BREAKPOINT && hwbreaks_ok)) {
-                eprintk("kgdbts: HW breakpoints BROKEN, ending tests\n");
-                return;
-        }
-        force_hwbrks = 1;
-        v1printk("kgdbts:Using HW breakpoints for SW breakpoint tests\n");
-#endif /* CONFIG_DEBUG_RODATA */
-}
-
 static void kgdbts_run_tests(void)
 {
         char *ptr;
@@ -1016,7 +1000,6 @@ static void kgdbts_run_tests(void)
                 v1printk("kgdbts:RUN access write breakpoint test\n");
                 run_hw_break_test(0);
         }
-        test_debug_rodata();
 
         /* required internal KGDB tests */
         v1printk("kgdbts:RUN plant and detach test\n");