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>
diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 34a5912..1e3de7d 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -410,13 +410,13 @@
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)