[v3,5/7] arm: kgdb: Handle read-only text / modules

Commit Message

Kees Cook Aug. 12, 2014, 6:24 p.m. UTC

From: Doug Anderson <[e-mail]>

Handle the case where someone has set the text segment of the kernel
as read-only by using the newly introduced "patch" mechanism.

Signed-off-by: Doug Anderson <[e-mail]>
Signed-off-by: Kees Cook <[e-mail]>
---
 arch/arm/kernel/Makefile |  2 +-
 arch/arm/kernel/kgdb.c   | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

Comments

Stephen Boyd Aug. 12, 2014, 7:38 p.m. UTC | #1

On 08/12/14 11:24, Kees Cook wrote:
> @@ -244,6 +248,32 @@ void kgdb_arch_exit(void)
>  	unregister_die_notifier(&kgdb_notifier);
>  }
>  
> +int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
> +{
> +	int err;
> +
> +	/* patch_text() only supports int-sized breakpoints */
> +	if (sizeof(int) != BREAK_INSTR_SIZE)
> +		return -EINVAL;

Could this be a BUILD_BUG_ON too?

Kees Cook Aug. 12, 2014, 7:40 p.m. UTC | #2

On Tue, Aug 12, 2014 at 12:38 PM, Stephen Boyd <[e-mail]> wrote:
> On 08/12/14 11:24, Kees Cook wrote:
>> @@ -244,6 +248,32 @@ void kgdb_arch_exit(void)
>>       unregister_die_notifier(&kgdb_notifier);
>>  }
>>
>> +int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
>> +{
>> +     int err;
>> +
>> +     /* patch_text() only supports int-sized breakpoints */
>> +     if (sizeof(int) != BREAK_INSTR_SIZE)
>> +             return -EINVAL;
>
> Could this be a BUILD_BUG_ON too?

Ah yes, good call. I'll adjust that.

Thanks!

-Kees

Patch

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 38ddd9f83d0e..70b730766330 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -67,7 +67,7 @@  test-kprobes-objs		+= kprobes-test-arm.o
 endif
 obj-$(CONFIG_OABI_COMPAT)	+= sys_oabi-compat.o
 obj-$(CONFIG_ARM_THUMBEE)	+= thumbee.o
-obj-$(CONFIG_KGDB)		+= kgdb.o
+obj-$(CONFIG_KGDB)		+= kgdb.o patch.o
 obj-$(CONFIG_ARM_UNWIND)	+= unwind.o
 obj-$(CONFIG_HAVE_TCM)		+= tcm.o
 obj-$(CONFIG_OF)		+= devtree.o
diff --git a/arch/arm/kernel/kgdb.c b/arch/arm/kernel/kgdb.c
index a74b53c1b7df..b2b9ccb6be59 100644
--- a/arch/arm/kernel/kgdb.c
+++ b/arch/arm/kernel/kgdb.c
@@ -12,8 +12,12 @@ 
 #include <linux/irq.h>
 #include <linux/kdebug.h>
 #include <linux/kgdb.h>
+#include <linux/uaccess.h>
+
 #include <asm/traps.h>
 
+#include "patch.h"
+
 struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] =
 {
 	{ "r0", 4, offsetof(struct pt_regs, ARM_r0)},
@@ -244,6 +248,32 @@  void kgdb_arch_exit(void)
 	unregister_die_notifier(&kgdb_notifier);
 }
 
+int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
+{
+	int err;
+
+	/* patch_text() only supports int-sized breakpoints */
+	if (sizeof(int) != BREAK_INSTR_SIZE)
+		return -EINVAL;
+
+	err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
+				BREAK_INSTR_SIZE);
+	if (err)
+		return err;
+
+	patch_text((void *)bpt->bpt_addr,
+		   *(unsigned int *)arch_kgdb_ops.gdb_bpt_instr);
+
+	return err;
+}
+
+int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
+{
+	patch_text((void *)bpt->bpt_addr, *(unsigned int *)bpt->saved_instr);
+
+	return 0;
+}
+
 /*
  * Register our undef instruction hooks with ARM undef core.
  * We regsiter a hook specifically looking for the KGB break inst