Commit 5ef22793 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Thomas Gleixner
Browse files

x86/entry: Re-order #DB handler to avoid *SAN instrumentation 



vmlinux.o: warning: objtool: exc_debug()+0xbb: call to clear_ti_thread_flag.constprop.0() leaves .noinstr.text section
vmlinux.o: warning: objtool: noist_exc_debug()+0x55: call to clear_ti_thread_flag.constprop.0() leaves .noinstr.text section

Rework things so that handle_debug() looses the noinstr and move the
clear_thread_flag() into that.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200603114052.127756554@infradead.org
parent 4b281e54

arch/x86/kernel/traps.c

+27 −28
Original line number Diff line number Diff line
@@ -775,26 +775,44 @@ static __always_inline void debug_exit(unsigned long dr7) 
 *

 * May run on IST stack.

 */

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

				 bool user_icebp)

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

{

	struct task_struct *tsk = current;

	bool user_icebp;

	int si_code;



	/*

	 * The SDM says "The processor clears the BTF flag when it

	 * generates a debug exception."  Clear TIF_BLOCKSTEP to keep

	 * TIF_BLOCKSTEP in sync with the hardware BTF flag.

	 */

	clear_thread_flag(TIF_BLOCKSTEP);



	/*

	 * If DR6 is zero, no point in trying to handle it. The kernel is

	 * not using INT1.

	 */

	if (!user && !dr6)

		return;



	/*

	 * If dr6 has no reason to give us about the origin of this trap,

	 * then it's very likely the result of an icebp/int01 trap.

	 * User wants a sigtrap for that.

	 */

	user_icebp = user && !dr6;



	/* Store the virtualized DR6 value */

	tsk->thread.debugreg6 = dr6;



	instrumentation_begin();

#ifdef CONFIG_KPROBES

	if (kprobe_debug_handler(regs)) {

		instrumentation_end();

		return;

	}

#endif



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

		       SIGTRAP) == NOTIFY_STOP) {

		instrumentation_end();

		return;

	}
@@ -825,7 +843,6 @@ static void noinstr handle_debug(struct pt_regs *regs, unsigned long dr6, 


out:

	cond_local_irq_disable(regs);

	instrumentation_end();

}



static __always_inline void exc_debug_kernel(struct pt_regs *regs,
@@ -834,14 +851,6 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs, 
	nmi_enter();

	instrumentation_begin();

	trace_hardirqs_off_finish();

	instrumentation_end();



	/*

	 * The SDM says "The processor clears the BTF flag when it

	 * generates a debug exception."  Clear TIF_BLOCKSTEP to keep

	 * TIF_BLOCKSTEP in sync with the hardware BTF flag.

	 */

	clear_thread_flag(TIF_BLOCKSTEP);



	/*

	 * Catch SYSENTER with TF set and clear DR_STEP. If this hit a
@@ -850,14 +859,8 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs, 
	if ((dr6 & DR_STEP) && is_sysenter_singlestep(regs))

		dr6 &= ~DR_STEP;



	/*

	 * If DR6 is zero, no point in trying to handle it. The kernel is

	 * not using INT1.

	 */

	if (dr6)

	handle_debug(regs, dr6, false);



	instrumentation_begin();

	if (regs->flags & X86_EFLAGS_IF)

		trace_hardirqs_on_prepare();

	instrumentation_end();
@@ -868,14 +871,10 @@ static __always_inline void exc_debug_user(struct pt_regs *regs, 
					   unsigned long dr6)

{

	idtentry_enter_user(regs);

	clear_thread_flag(TIF_BLOCKSTEP);

	instrumentation_begin();



	/*

	 * If dr6 has no reason to give us about the origin of this trap,

	 * then it's very likely the result of an icebp/int01 trap.

	 * User wants a sigtrap for that.

	 */

	handle_debug(regs, dr6, !dr6);

	handle_debug(regs, dr6, true);

	instrumentation_end();

	idtentry_exit_user(regs);

}

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