x86: debugctlmsr arch_has_block_step
This implements user-mode step-until-branch on x86 using the BTF bit
in MSR_IA32_DEBUGCTLMSR. It's just like single-step, only less so.
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 243bff6..cf4b9da 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -107,7 +107,10 @@
return 0;
}
-void user_enable_single_step(struct task_struct *child)
+/*
+ * Enable single-stepping. Return nonzero if user mode is not using TF itself.
+ */
+static int enable_single_step(struct task_struct *child)
{
struct pt_regs *regs = task_pt_regs(child);
@@ -122,7 +125,7 @@
* If TF was already set, don't do anything else
*/
if (regs->eflags & X86_EFLAGS_TF)
- return;
+ return 0;
/* Set TF on the kernel stack.. */
regs->eflags |= X86_EFLAGS_TF;
@@ -133,13 +136,68 @@
* won't clear it by hand later.
*/
if (is_setting_trap_flag(child, regs))
- return;
+ return 0;
set_tsk_thread_flag(child, TIF_FORCED_TF);
+
+ return 1;
+}
+
+/*
+ * Install this value in MSR_IA32_DEBUGCTLMSR whenever child is running.
+ */
+static void write_debugctlmsr(struct task_struct *child, unsigned long val)
+{
+ child->thread.debugctlmsr = val;
+
+ if (child != current)
+ return;
+
+#ifdef CONFIG_X86_64
+ wrmsrl(MSR_IA32_DEBUGCTLMSR, val);
+#else
+ wrmsr(MSR_IA32_DEBUGCTLMSR, val, 0);
+#endif
+}
+
+/*
+ * Enable single or block step.
+ */
+static void enable_step(struct task_struct *child, bool block)
+{
+ /*
+ * Make sure block stepping (BTF) is not enabled unless it should be.
+ * Note that we don't try to worry about any is_setting_trap_flag()
+ * instructions after the first when using block stepping.
+ * So noone should try to use debugger block stepping in a program
+ * that uses user-mode single stepping itself.
+ */
+ if (enable_single_step(child) && block) {
+ set_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
+ write_debugctlmsr(child, DEBUGCTLMSR_BTF);
+ } else if (test_and_clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR)) {
+ write_debugctlmsr(child, 0);
+ }
+}
+
+void user_enable_single_step(struct task_struct *child)
+{
+ enable_step(child, 0);
+}
+
+void user_enable_block_step(struct task_struct *child)
+{
+ enable_step(child, 1);
}
void user_disable_single_step(struct task_struct *child)
{
+ /*
+ * Make sure block stepping (BTF) is disabled.
+ */
+ if (test_and_clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR))
+ write_debugctlmsr(child, 0);
+
/* Always clear TIF_SINGLESTEP... */
clear_tsk_thread_flag(child, TIF_SINGLESTEP);