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Date: Thu, 29 Mar 2012 17:49:02 -0500
From: Jason Wessel <jason.wessel@...driver.com>
To: <linux-kernel@...r.kernel.org>
CC: <kgdb-bugreport@...ts.sourceforge.net>
Subject: [PATCH 6/6] 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@...nel.org
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: stable@...r.kernel.org # >= 2.6.36
Inspried-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
---
arch/x86/kernel/kgdb.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/kgdb.h | 3 ++-
2 files changed, 62 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index fdc37b3..b9bd9d8 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -43,6 +43,8 @@
#include <linux/smp.h>
#include <linux/nmi.h>
#include <linux/hw_breakpoint.h>
+#include <linux/uaccess.h>
+#include <linux/memory.h>
#include <asm/debugreg.h>
#include <asm/apicdef.h>
@@ -742,6 +744,64 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long ip)
regs->ip = ip;
}
+int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
+{
+ int err;
+ char opc[BREAK_INSTR_SIZE];
+
+ bpt->type = BP_BREAKPOINT;
+ err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
+ BREAK_INSTR_SIZE);
+ if (err)
+ return err;
+ err = probe_kernel_write((char *)bpt->bpt_addr,
+ arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
+#ifdef CONFIG_DEBUG_RODATA
+ if (!err)
+ return err;
+ /*
+ * It is safe to call text_poke() because normal kernel execution
+ * is stopped on all cores, so long as the text_mutex is not locked.
+ */
+ if (mutex_is_locked(&text_mutex))
+ return -EBUSY;
+ text_poke((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr,
+ BREAK_INSTR_SIZE);
+ err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);
+ if (err)
+ return err;
+ if (memcmp(opc, arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE))
+ return -EINVAL;
+ bpt->type = BP_POKE_BREAKPOINT;
+#endif /* CONFIG_DEBUG_RODATA */
+ return err;
+}
+
+int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
+{
+#ifdef CONFIG_DEBUG_RODATA
+ int err;
+ char opc[BREAK_INSTR_SIZE];
+
+ if (bpt->type != BP_POKE_BREAKPOINT)
+ goto knl_write;
+ /*
+ * It is safe to call text_poke() because normal kernel execution
+ * is stopped on all cores, so long as the text_mutex is not locked.
+ */
+ if (mutex_is_locked(&text_mutex))
+ goto knl_write;
+ text_poke((void *)bpt->bpt_addr, bpt->saved_instr, BREAK_INSTR_SIZE);
+ err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);
+ if (err || memcmp(opc, bpt->saved_instr, BREAK_INSTR_SIZE))
+ goto knl_write;
+ return err;
+knl_write:
+#endif /* CONFIG_DEBUG_RODATA */
+ return probe_kernel_write((char *)bpt->bpt_addr,
+ (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
+}
+
struct kgdb_arch arch_kgdb_ops = {
/* Breakpoint instruction: */
.gdb_bpt_instr = { 0xcc },
diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index e5d689c..c4d2fc1 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -63,7 +63,8 @@ enum kgdb_bptype {
BP_HARDWARE_BREAKPOINT,
BP_WRITE_WATCHPOINT,
BP_READ_WATCHPOINT,
- BP_ACCESS_WATCHPOINT
+ BP_ACCESS_WATCHPOINT,
+ BP_POKE_BREAKPOINT,
};
enum kgdb_bpstate {
--
1.7.9.4
--
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