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authorJason Wessel <jason.wessel@windriver.com>2012-03-23 18:35:05 +0400
committerJason Wessel <jason.wessel@windriver.com>2012-03-30 02:41:25 +0400
commit3751d3e85cf693e10e2c47c03c8caa65e171099b (patch)
tree65d123dac17103f6862831bcb4271b263805fd9f /arch/x86/kernel/kgdb.c
parent98b54aa1a2241b59372468bd1e9c2d207bdba54b (diff)
downloadlinux-3751d3e85cf693e10e2c47c03c8caa65e171099b.tar.xz
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>
Diffstat (limited to 'arch/x86/kernel/kgdb.c')
-rw-r--r--arch/x86/kernel/kgdb.c60
1 files changed, 60 insertions, 0 deletions
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index fdc37b3d0ce3..b9bd9d8de665 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 },