x86: prevent unconditional writes to DebugCtl MSR

Otherwise, enabling (or better, subsequent disabling) of single stepping would cause a kernel oops on CPUs not having this MSR. The patch could have been added a conditional to the MSR write in user_disable_single_step(), but centralizing the updates seems safer and (looking forward) better manageable. Signed-off-by: Jan Beulich <jbeulich@novell.com> Cc: Markus Metzger <markus.t.metzger@intel.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
git-mirror · Apr 17, 2008 · 5b0e508 · 5b0e508
1 parent f694010
commit 5b0e508
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Showing 5 changed files with 16 additions and 7 deletions.
diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
@@ -410,13 +410,13 @@ static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 static void __kprobes clear_btf(void)
 {
 	if (test_thread_flag(TIF_DEBUGCTLMSR))
-		wrmsrl(MSR_IA32_DEBUGCTLMSR, 0);
+		update_debugctlmsr(0);
 }
 
 static void __kprobes restore_btf(void)
 {
 	if (test_thread_flag(TIF_DEBUGCTLMSR))
-		wrmsrl(MSR_IA32_DEBUGCTLMSR, current->thread.debugctlmsr);
+		update_debugctlmsr(current->thread.debugctlmsr);
 }
 
 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)

diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
@@ -564,12 +564,12 @@ __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
 		/* we clear debugctl to make sure DS
 		 * is not in use when we change it */
 		debugctl = 0;
-		wrmsrl(MSR_IA32_DEBUGCTLMSR, 0);
+		update_debugctlmsr(0);
 		wrmsr(MSR_IA32_DS_AREA, next->ds_area_msr, 0);
 	}
 
 	if (next->debugctlmsr != debugctl)
-		wrmsr(MSR_IA32_DEBUGCTLMSR, next->debugctlmsr, 0);
+		update_debugctlmsr(next->debugctlmsr);
 
 	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
 		set_debugreg(next->debugreg0, 0);

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
@@ -563,12 +563,12 @@ static inline void __switch_to_xtra(struct task_struct *prev_p,
 		/* we clear debugctl to make sure DS
 		 * is not in use when we change it */
 		debugctl = 0;
-		wrmsrl(MSR_IA32_DEBUGCTLMSR, 0);
+		update_debugctlmsr(0);
 		wrmsrl(MSR_IA32_DS_AREA, next->ds_area_msr);
 	}
 
 	if (next->debugctlmsr != debugctl)
-		wrmsrl(MSR_IA32_DEBUGCTLMSR, next->debugctlmsr);
+		update_debugctlmsr(next->debugctlmsr);
 
 	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
 		loaddebug(next, 0);

diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
@@ -148,7 +148,7 @@ static void write_debugctlmsr(struct task_struct *child, unsigned long val)
 	if (child != current)
 		return;
 
-	wrmsrl(MSR_IA32_DEBUGCTLMSR, val);
+	update_debugctlmsr(val);
 }
 
 /*

diff --git a/include/asm-x86/processor.h b/include/asm-x86/processor.h
@@ -741,6 +741,15 @@ extern void switch_to_new_gdt(void);
 extern void cpu_init(void);
 extern void init_gdt(int cpu);
 
+static inline void update_debugctlmsr(unsigned long debugctlmsr)
+{
+#ifndef CONFIG_X86_DEBUGCTLMSR
+	if (boot_cpu_data.x86 < 6)
+		return;
+#endif
+	wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctlmsr);
+}
+
 /*
  * from system description table in BIOS. Mostly for MCA use, but
  * others may find it useful:
-Original file line number
+Diff line change
@@ Expand Up @@
     	if (child != current)
     		return;
-    	wrmsrl(MSR_IA32_DEBUGCTLMSR, val);
+    	update_debugctlmsr(val);
     }
     /*
@@ Expand Down @@