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x86: prevent unconditional writes to DebugCtl MSR

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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>
This commit is contained in:
Jan Beulich
2008-03-10 13:11:17 +00:00
committed by Ingo Molnar
parent f694010185
commit 5b0e508415
5 changed files with 16 additions and 7 deletions
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4
arch/x86/kernel/kprobes.c
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@@ -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)