X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=arch%2Fx86%2Fkernel%2Fstep.c;h=e8b9863ef8c4f8d09f10344d868450711add7ee5;hb=eb4225b2da2b9f3c1ee43efe58ed1415cc1d4c47;hp=2ef1a5f8d6758043b6ce2204da47cb71e5cc1614;hpb=8f859016ea49cd8d7c743533bd1ab3db9a813ffa;p=pandora-kernel.git

diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 2ef1a5f8d675..e8b9863ef8c4 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -105,6 +105,20 @@ static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
 static int enable_single_step(struct task_struct *child)
 {
 	struct pt_regs *regs = task_pt_regs(child);
+	unsigned long oflags;
+
+	/*
+	 * If we stepped into a sysenter/syscall insn, it trapped in
+	 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
+	 * If user-mode had set TF itself, then it's still clear from
+	 * do_debug() and we need to set it again to restore the user
+	 * state so we don't wrongly set TIF_FORCED_TF below.
+	 * If enable_single_step() was used last and that is what
+	 * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are
+	 * already set and our bookkeeping is fine.
+	 */
+	if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
+		regs->flags |= X86_EFLAGS_TF;
 
 	/*
 	 * Always set TIF_SINGLESTEP - this guarantees that
@@ -113,11 +127,7 @@ static int enable_single_step(struct task_struct *child)
 	 */
 	set_tsk_thread_flag(child, TIF_SINGLESTEP);
 
-	/*
-	 * If TF was already set, don't do anything else
-	 */
-	if (regs->flags & X86_EFLAGS_TF)
-		return 0;
+	oflags = regs->flags;
 
 	/* Set TF on the kernel stack.. */
 	regs->flags |= X86_EFLAGS_TF;
@@ -126,9 +136,22 @@ static int enable_single_step(struct task_struct *child)
 	 * ..but if TF is changed by the instruction we will trace,
 	 * don't mark it as being "us" that set it, so that we
 	 * won't clear it by hand later.
+	 *
+	 * Note that if we don't actually execute the popf because
+	 * of a signal arriving right now or suchlike, we will lose
+	 * track of the fact that it really was "us" that set it.
 	 */
-	if (is_setting_trap_flag(child, regs))
+	if (is_setting_trap_flag(child, regs)) {
+		clear_tsk_thread_flag(child, TIF_FORCED_TF);
 		return 0;
+	}
+
+	/*
+	 * If TF was already set, check whether it was us who set it.
+	 * If not, we should never attempt a block step.
+	 */
+	if (oflags & X86_EFLAGS_TF)
+		return test_tsk_thread_flag(child, TIF_FORCED_TF);
 
 	set_tsk_thread_flag(child, TIF_FORCED_TF);
 
@@ -140,12 +163,15 @@ static int enable_single_step(struct task_struct *child)
  */
 static void write_debugctlmsr(struct task_struct *child, unsigned long val)
 {
+	if (child->thread.debugctlmsr == val)
+		return;
+
 	child->thread.debugctlmsr = val;
 
 	if (child != current)
 		return;
 
-	wrmsrl(MSR_IA32_DEBUGCTLMSR, val);
+	update_debugctlmsr(val);
 }
 
 /*
@@ -165,11 +191,11 @@ static void enable_step(struct task_struct *child, bool block)
 		write_debugctlmsr(child,
 				  child->thread.debugctlmsr | DEBUGCTLMSR_BTF);
 	} else {
-	    write_debugctlmsr(child,
-			      child->thread.debugctlmsr & ~TIF_DEBUGCTLMSR);
+		write_debugctlmsr(child,
+				  child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF);
 
-	    if (!child->thread.debugctlmsr)
-		    clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
+		if (!child->thread.debugctlmsr)
+			clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
 	}
 }
 
@@ -189,7 +215,7 @@ void user_disable_single_step(struct task_struct *child)
 	 * Make sure block stepping (BTF) is disabled.
 	 */
 	write_debugctlmsr(child,
-			  child->thread.debugctlmsr & ~TIF_DEBUGCTLMSR);
+			  child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF);
 
 	if (!child->thread.debugctlmsr)
 		clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);