Commit 4eb5acc3 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Thomas Gleixner
Browse files

x86/debug: Move historical SYSENTER junk into exc_debug_kernel() 



The historical SYSENTER junk is explicitly for from-kernel, so move it
to the #DB-from-kernel handler.

It is ordered after the notifier, which is important for KGDB which uses TF
single-step and needs to consume the event before that point.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarDaniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20200902133201.031099736@infradead.org
parent 4182e943

arch/x86/kernel/traps.c

+25 −24
Original line number Diff line number Diff line
@@ -783,7 +783,7 @@ static __always_inline unsigned long debug_read_clear_dr6(void) 
 *

 * May run on IST stack.

 */

static void handle_debug(struct pt_regs *regs, unsigned long dr6)

static bool handle_debug(struct pt_regs *regs, unsigned long *dr6)

{

	struct task_struct *tsk = current;

	bool icebp;
@@ -793,15 +793,13 @@ static void handle_debug(struct pt_regs *regs, unsigned long dr6) 
	 * then it's very likely the result of an icebp/int01 trap.

	 * User wants a sigtrap for that.

	 */

	icebp = !dr6;

	icebp = !*dr6;



	/* Store the virtualized DR6 value */

	tsk->thread.debugreg6 = dr6;

	tsk->thread.debugreg6 = *dr6;



	if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, 0,

		       SIGTRAP) == NOTIFY_STOP) {

		return;

	}

	if (notify_die(DIE_DEBUG, "debug", regs, (long)dr6, 0, SIGTRAP) == NOTIFY_STOP)

		return true;



	/* It's safe to allow irq's after DR6 has been saved */

	cond_local_irq_enable(regs);
@@ -815,25 +813,15 @@ static void handle_debug(struct pt_regs *regs, unsigned long dr6) 
	/*

	 * Reload dr6, the notifier might have changed it.

	 */

	dr6 = tsk->thread.debugreg6;

	*dr6 = tsk->thread.debugreg6;



	if (WARN_ON_ONCE((dr6 & DR_STEP) && !user_mode(regs))) {

		/*

		 * Historical junk that used to handle SYSENTER single-stepping.

		 * This should be unreachable now.  If we survive for a while

		 * without anyone hitting this warning, we'll turn this into

		 * an oops.

		 */

		tsk->thread.debugreg6 &= ~DR_STEP;

		set_tsk_thread_flag(tsk, TIF_SINGLESTEP);

		regs->flags &= ~X86_EFLAGS_TF;

	}



	if (dr6 & (DR_STEP | DR_TRAP_BITS) || icebp)

		send_sigtrap(regs, 0, get_si_code(dr6));

	if (*dr6 & (DR_STEP | DR_TRAP_BITS) || icebp)

		send_sigtrap(regs, 0, get_si_code(*dr6));



out:

	cond_local_irq_disable(regs);



	return false;

}



static __always_inline void exc_debug_kernel(struct pt_regs *regs,
@@ -876,7 +864,20 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs, 
	if (!dr6)

		goto out;



	handle_debug(regs, dr6);

	if (handle_debug(regs, &dr6))

		goto out;



	if (WARN_ON_ONCE(dr6 & DR_STEP)) {

		/*

		 * Historical junk that used to handle SYSENTER single-stepping.

		 * This should be unreachable now.  If we survive for a while

		 * without anyone hitting this warning, we'll turn this into

		 * an oops.

		 */

		dr6 &= ~DR_STEP;

		set_thread_flag(TIF_SINGLESTEP);

		regs->flags &= ~X86_EFLAGS_TF;

	}



out:

	instrumentation_end();
@@ -906,7 +907,7 @@ static __always_inline void exc_debug_user(struct pt_regs *regs, 
	irqentry_enter_from_user_mode(regs);

	instrumentation_begin();



	handle_debug(regs, dr6);

	handle_debug(regs, &dr6);



	instrumentation_end();

	irqentry_exit_to_user_mode(regs);

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