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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: 248591f5d2 ("kcsan: Make KCSAN compatible with new IRQ state tracking")
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200729110916.3920464-2-elver@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Marco Elver 2020-07-29 13:09:16 +02:00 committed by Ingo Molnar
parent 0584df9c12
commit 92c209ac6d
4 changed files with 37 additions and 0 deletions
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4
include/linux/sched.h
View File

@ -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

23
kernel/kcsan/core.c
View File

@ -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);
}

7
kernel/kcsan/kcsan.h
View File

@ -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.
*/

3
kernel/kcsan/report.c
View File

@ -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);