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: 248591f5d257 ("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>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 52e0fdd6a555220e4b6825d137ae342c6c774d50..060e9214c8b5cc398455ed6bf59fb5f01607f07e 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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

diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index 732623c30359f7b64e7de57a453563bcff316fef..0fe0681927811c6dcacedec2dea334e36da6ed75 100644 (file)
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -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);
 }

diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
index 763d6d08d94bb6be7fa943f0709f0d21b3556863..29480010dc3028396782d7ba9185451c1f45e29b 100644 (file)
--- a/kernel/kcsan/kcsan.h
+++ b/kernel/kcsan/kcsan.h
@@ -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.
  */

diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index 6b2fb1a6d8cd597ef96ec47cf4e95343cb68e0fb..9d07e175de0f8f6d57794898361a5b41e82454a8 100644 (file)
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -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);