x86, ptrace: Fix block-step

Implement ptrace-block-step using TIF_BLOCKSTEP which will set
DEBUGCTLMSR_BTF when set for a task while preserving any other
DEBUGCTLMSR bits.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100325135414.017536066@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

6 files changed, 53 insertions, 9 deletions

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 5bec21a66dc..32428b410b5 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -799,7 +799,7 @@ extern void cpu_init(void);
 
 static inline unsigned long get_debugctlmsr(void)
 {
-    unsigned long debugctlmsr = 0;
+        unsigned long debugctlmsr = 0;
 
 #ifndef CONFIG_X86_DEBUGCTLMSR
         if (boot_cpu_data.x86 < 6)
@@ -807,7 +807,7 @@ static inline unsigned long get_debugctlmsr(void)
 #endif
         rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctlmsr);
 
-    return debugctlmsr;
+        return debugctlmsr;
 }
 
 static inline void update_debugctlmsr(unsigned long debugctlmsr)
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index dc85e12d140..d017ed5502e 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -92,6 +92,7 @@ struct thread_info {
 #define TIF_IO_BITMAP           22      /* uses I/O bitmap */
 #define TIF_FREEZE              23      /* is freezing for suspend */
 #define TIF_FORCED_TF           24      /* true if TF in eflags artificially */
+#define TIF_BLOCKSTEP           25      /* set when we want DEBUGCTLMSR_BTF */
 #define TIF_LAZY_MMU_UPDATES    27      /* task is updating the mmu lazily */
 #define TIF_SYSCALL_TRACEPOINT  28      /* syscall tracepoint instrumentation */
 
@@ -113,6 +114,7 @@ struct thread_info {
 #define _TIF_IO_BITMAP          (1 << TIF_IO_BITMAP)
 #define _TIF_FREEZE             (1 << TIF_FREEZE)
 #define _TIF_FORCED_TF          (1 << TIF_FORCED_TF)
+#define _TIF_BLOCKSTEP          (1 << TIF_BLOCKSTEP)
 #define _TIF_LAZY_MMU_UPDATES   (1 << TIF_LAZY_MMU_UPDATES)
 #define _TIF_SYSCALL_TRACEPOINT (1 << TIF_SYSCALL_TRACEPOINT)
 
@@ -143,7 +145,7 @@ struct thread_info {
 
 /* flags to check in __switch_to() */
 #define _TIF_WORK_CTXSW                                                 \
-        (_TIF_IO_BITMAP|_TIF_NOTSC)
+        (_TIF_IO_BITMAP|_TIF_NOTSC|_TIF_BLOCKSTEP)
 
 #define _TIF_WORK_CTXSW_PREV (_TIF_WORK_CTXSW|_TIF_USER_RETURN_NOTIFY)
 #define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW|_TIF_DEBUG)
diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 7a880ad3a20..f2f56c0967b 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -422,12 +422,22 @@ static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 
 static void __kprobes clear_btf(void)
 {
-        /* XXX */
+        if (test_thread_flag(TIF_BLOCKSTEP)) {
+                unsigned long debugctl = get_debugctlmsr();
+
+                debugctl &= ~DEBUGCTLMSR_BTF;
+                update_debugctlmsr(debugctl);
+        }
 }
 
 static void __kprobes restore_btf(void)
 {
-        /* XXX */
+        if (test_thread_flag(TIF_BLOCKSTEP)) {
+                unsigned long debugctl = get_debugctlmsr();
+
+                debugctl |= DEBUGCTLMSR_BTF;
+                update_debugctlmsr(debugctl);
+        }
 }
 
 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 1a60beb32ed..8328009416d 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -195,6 +195,17 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
         prev = &prev_p->thread;
         next = &next_p->thread;
 
+        if (test_tsk_thread_flag(prev_p, TIF_BLOCKSTEP) ^
+            test_tsk_thread_flag(next_p, TIF_BLOCKSTEP)) {
+                unsigned long debugctl = get_debugctlmsr();
+
+                debugctl &= ~DEBUGCTLMSR_BTF;
+                if (test_tsk_thread_flag(next_p, TIF_BLOCKSTEP))
+                        debugctl |= DEBUGCTLMSR_BTF;
+
+                update_debugctlmsr(debugctl);
+        }
+
         if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^
             test_tsk_thread_flag(next_p, TIF_NOTSC)) {
                 /* prev and next are different */
diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 7beba0769a8..58de45ee08b 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -169,9 +169,19 @@ static void enable_step(struct task_struct *child, bool block)
          * So noone should try to use debugger block stepping in a program
          * that uses user-mode single stepping itself.
          */
-        if (!enable_single_step(child))
-                return;
-        /* XXX */
+        if (enable_single_step(child) && block) {
+                unsigned long debugctl = get_debugctlmsr();
+
+                debugctl |= DEBUGCTLMSR_BTF;
+                update_debugctlmsr(debugctl);
+                set_tsk_thread_flag(child, TIF_BLOCKSTEP);
+        } else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) {
+                unsigned long debugctl = get_debugctlmsr();
+
+                debugctl &= ~DEBUGCTLMSR_BTF;
+                update_debugctlmsr(debugctl);
+                clear_tsk_thread_flag(child, TIF_BLOCKSTEP);
+        }
 }
 
 void user_enable_single_step(struct task_struct *child)
@@ -189,7 +199,13 @@ void user_disable_single_step(struct task_struct *child)
         /*
          * Make sure block stepping (BTF) is disabled.
          */
-        /* XXX */
+        if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) {
+                unsigned long debugctl = get_debugctlmsr();
+
+                debugctl &= ~DEBUGCTLMSR_BTF;
+                update_debugctlmsr(debugctl);
+                clear_tsk_thread_flag(child, TIF_BLOCKSTEP);
+        }
 
         /* Always clear TIF_SINGLESTEP... */
         clear_tsk_thread_flag(child, TIF_SINGLESTEP);
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index e3da5d726a3..36f1bd9f8e7 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -544,6 +544,11 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
         /* DR6 may or may not be cleared by the CPU */
         set_debugreg(0, 6);
 
+        /*
+         * The processor cleared BTF, so don't mark that we need it set.
+         */
+        clear_tsk_thread_flag(tsk, TIF_BLOCKSTEP);
+
         /* Store the virtualized DR6 value */
         tsk->thread.debugreg6 = dr6;