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 <[email protected]>
---
arch/x86/kernel/step.c | 64 +++++++++++++++++++++++++++++++++++++++++--
arch/x86/kernel/traps_32.c | 6 ++++
arch/x86/kernel/traps_64.c | 6 ++++
include/asm-x86/ptrace.h | 7 +++++
4 files changed, 80 insertions(+), 3 deletions(-)
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 @@ static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
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 @@ void user_enable_single_step(struct task_struct *child)
* 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 @@ void user_enable_single_step(struct task_struct *child)
* 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);
diff --git a/arch/x86/kernel/traps_32.c b/arch/x86/kernel/traps_32.c
index 298d13e..03d5b41 100644
--- a/arch/x86/kernel/traps_32.c
+++ b/arch/x86/kernel/traps_32.c
@@ -830,6 +830,12 @@ fastcall void __kprobes do_debug(struct pt_regs * regs, long error_code)
get_debugreg(condition, 6);
+ /*
+ * The processor cleared BTF, so don't mark that we need it set.
+ */
+ clear_tsk_thread_flag(tsk, TIF_DEBUGCTLMSR);
+ tsk->thread.debugctlmsr = 0;
+
if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
SIGTRAP) == NOTIFY_STOP)
return;
diff --git a/arch/x86/kernel/traps_64.c b/arch/x86/kernel/traps_64.c
index daf35a8..ec70f5c 100644
--- a/arch/x86/kernel/traps_64.c
+++ b/arch/x86/kernel/traps_64.c
@@ -848,6 +848,12 @@ asmlinkage void __kprobes do_debug(struct pt_regs * regs,
get_debugreg(condition, 6);
+ /*
+ * The processor cleared BTF, so don't mark that we need it set.
+ */
+ clear_tsk_thread_flag(tsk, TIF_DEBUGCTLMSR);
+ tsk->thread.debugctlmsr = 0;
+
if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
SIGTRAP) == NOTIFY_STOP)
return;
diff --git a/include/asm-x86/ptrace.h b/include/asm-x86/ptrace.h
index d223dec..04204f3 100644
--- a/include/asm-x86/ptrace.h
+++ b/include/asm-x86/ptrace.h
@@ -150,6 +150,13 @@ enum {
extern void user_enable_single_step(struct task_struct *);
extern void user_disable_single_step(struct task_struct *);
+extern void user_enable_block_step(struct task_struct *);
+#ifdef CONFIG_X86_DEBUGCTLMSR
+#define arch_has_block_step() (1)
+#else
+#define arch_has_block_step() (boot_cpu_data.x86 >= 6)
+#endif
+
struct user_desc;
extern int do_get_thread_area(struct task_struct *p, int idx,
struct user_desc __user *info);
-
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