Commit 92c209ac authored by Marco Elver's avatar Marco Elver Committed by Ingo Molnar
Browse files

kcsan: Improve IRQ state trace reporting 



To improve the general usefulness of the IRQ state trace events with
KCSAN enabled, save and restore the trace information when entering and
exiting the KCSAN runtime as well as when generating a KCSAN report.

Without this, reporting the IRQ trace events (whether via a KCSAN report
or outside of KCSAN via a lockdep report) is rather useless due to
continuously being touched by KCSAN. This is because if KCSAN is
enabled, every instrumented memory access causes changes to IRQ trace
events (either by KCSAN disabling/enabling interrupts or taking
report_lock when generating a report).

Before "lockdep: Prepare for NMI IRQ state tracking", KCSAN avoided
touching the IRQ trace events via raw_local_irq_save/restore() and
lockdep_off/on().

Fixes: 248591f5 ("kcsan: Make KCSAN compatible with new IRQ state tracking")
Signed-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200729110916.3920464-2-elver@google.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 0584df9c

include/linux/sched.h

+4 −0
Original line number Diff line number Diff line
@@ -1184,8 +1184,12 @@ struct task_struct { 
#ifdef CONFIG_KASAN

	unsigned int			kasan_depth;

#endif



#ifdef CONFIG_KCSAN

	struct kcsan_ctx		kcsan_ctx;

#ifdef CONFIG_TRACE_IRQFLAGS

	struct irqtrace_events		kcsan_save_irqtrace;

#endif

#endif



#ifdef CONFIG_FUNCTION_GRAPH_TRACER

kernel/kcsan/core.c

+23 −0
Original line number Diff line number Diff line
@@ -291,6 +291,20 @@ static inline unsigned int get_delay(void) 
				0);

}



void kcsan_save_irqtrace(struct task_struct *task)

{

#ifdef CONFIG_TRACE_IRQFLAGS

	task->kcsan_save_irqtrace = task->irqtrace;

#endif

}



void kcsan_restore_irqtrace(struct task_struct *task)

{

#ifdef CONFIG_TRACE_IRQFLAGS

	task->irqtrace = task->kcsan_save_irqtrace;

#endif

}



/*

 * Pull everything together: check_access() below contains the performance

 * critical operations; the fast-path (including check_access) functions should
@@ -336,9 +350,11 @@ static noinline void kcsan_found_watchpoint(const volatile void *ptr, 
	flags = user_access_save();



	if (consumed) {

		kcsan_save_irqtrace(current);

		kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE,

			     KCSAN_REPORT_CONSUMED_WATCHPOINT,

			     watchpoint - watchpoints);

		kcsan_restore_irqtrace(current);

	} else {

		/*

		 * The other thread may not print any diagnostics, as it has
@@ -396,6 +412,12 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) 
		goto out;

	}



	/*

	 * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's

	 * runtime is entered for every memory access, and potentially useful

	 * information is lost if dirtied by KCSAN.

	 */

	kcsan_save_irqtrace(current);

	if (!kcsan_interrupt_watcher)

		local_irq_save(irq_flags);
@@ -539,6 +561,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) 
out_unlock:

	if (!kcsan_interrupt_watcher)

		local_irq_restore(irq_flags);

	kcsan_restore_irqtrace(current);

out:

	user_access_restore(ua_flags);

}

kernel/kcsan/kcsan.h

+7 −0
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ 
#define _KERNEL_KCSAN_KCSAN_H



#include <linux/kcsan.h>

#include <linux/sched.h>



/* The number of adjacent watchpoints to check. */

#define KCSAN_CHECK_ADJACENT 1
@@ -22,6 +23,12 @@ extern unsigned int kcsan_udelay_interrupt; 
 */

extern bool kcsan_enabled;



/*

 * Save/restore IRQ flags state trace dirtied by KCSAN.

 */

void kcsan_save_irqtrace(struct task_struct *task);

void kcsan_restore_irqtrace(struct task_struct *task);



/*

 * Initialize debugfs file.

 */

kernel/kcsan/report.c

+3 −0
Original line number Diff line number Diff line
@@ -308,6 +308,9 @@ static void print_verbose_info(struct task_struct *task) 
	if (!task)

		return;



	/* Restore IRQ state trace for printing. */

	kcsan_restore_irqtrace(task);



	pr_err("\n");

	debug_show_held_locks(task);

	print_irqtrace_events(task);

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