[PATCH 6/8] arm: kgdb: Handle read-only text / modules

Kees Cook
2014-08-07T15:03:57Z

From: Doug Anderson <dianders@chromium.org>

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 <dianders@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/arm/kernel/Makefile | 2 +-
arch/arm/kernel/kgdb.c | 30 ++++++++++++++++++++++++++++++
2 files changed, 31 insertions(+), 1 deletion(-)

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
--
1.9.1