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-rw-r--r--kernel/kcsan/report.c515
1 files changed, 515 insertions, 0 deletions
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
new file mode 100644
index 000000000000..11c791b886f3
--- /dev/null
+++ b/kernel/kcsan/report.c
@@ -0,0 +1,515 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/jiffies.h>
+#include <linux/kernel.h>
+#include <linux/lockdep.h>
+#include <linux/preempt.h>
+#include <linux/printk.h>
+#include <linux/sched.h>
+#include <linux/spinlock.h>
+#include <linux/stacktrace.h>
+
+#include "kcsan.h"
+#include "encoding.h"
+
+/*
+ * Max. number of stack entries to show in the report.
+ */
+#define NUM_STACK_ENTRIES 64
+
+/*
+ * Other thread info: communicated from other racing thread to thread that set
+ * up the watchpoint, which then prints the complete report atomically. Only
+ * need one struct, as all threads should to be serialized regardless to print
+ * the reports, with reporting being in the slow-path.
+ */
+static struct {
+ const volatile void *ptr;
+ size_t size;
+ int access_type;
+ int task_pid;
+ int cpu_id;
+ unsigned long stack_entries[NUM_STACK_ENTRIES];
+ int num_stack_entries;
+} other_info = { .ptr = NULL };
+
+/*
+ * Information about reported races; used to rate limit reporting.
+ */
+struct report_time {
+ /*
+ * The last time the race was reported.
+ */
+ unsigned long time;
+
+ /*
+ * The frames of the 2 threads; if only 1 thread is known, one frame
+ * will be 0.
+ */
+ unsigned long frame1;
+ unsigned long frame2;
+};
+
+/*
+ * Since we also want to be able to debug allocators with KCSAN, to avoid
+ * deadlock, report_times cannot be dynamically resized with krealloc in
+ * rate_limit_report.
+ *
+ * Therefore, we use a fixed-size array, which at most will occupy a page. This
+ * still adequately rate limits reports, assuming that a) number of unique data
+ * races is not excessive, and b) occurrence of unique races within the
+ * same time window is limited.
+ */
+#define REPORT_TIMES_MAX (PAGE_SIZE / sizeof(struct report_time))
+#define REPORT_TIMES_SIZE \
+ (CONFIG_KCSAN_REPORT_ONCE_IN_MS > REPORT_TIMES_MAX ? \
+ REPORT_TIMES_MAX : \
+ CONFIG_KCSAN_REPORT_ONCE_IN_MS)
+static struct report_time report_times[REPORT_TIMES_SIZE];
+
+/*
+ * This spinlock protects reporting and other_info, since other_info is usually
+ * required when reporting.
+ */
+static DEFINE_SPINLOCK(report_lock);
+
+/*
+ * Checks if the race identified by thread frames frame1 and frame2 has
+ * been reported since (now - KCSAN_REPORT_ONCE_IN_MS).
+ */
+static bool rate_limit_report(unsigned long frame1, unsigned long frame2)
+{
+ struct report_time *use_entry = &report_times[0];
+ unsigned long invalid_before;
+ int i;
+
+ BUILD_BUG_ON(CONFIG_KCSAN_REPORT_ONCE_IN_MS != 0 && REPORT_TIMES_SIZE == 0);
+
+ if (CONFIG_KCSAN_REPORT_ONCE_IN_MS == 0)
+ return false;
+
+ invalid_before = jiffies - msecs_to_jiffies(CONFIG_KCSAN_REPORT_ONCE_IN_MS);
+
+ /* Check if a matching race report exists. */
+ for (i = 0; i < REPORT_TIMES_SIZE; ++i) {
+ struct report_time *rt = &report_times[i];
+
+ /*
+ * Must always select an entry for use to store info as we
+ * cannot resize report_times; at the end of the scan, use_entry
+ * will be the oldest entry, which ideally also happened before
+ * KCSAN_REPORT_ONCE_IN_MS ago.
+ */
+ if (time_before(rt->time, use_entry->time))
+ use_entry = rt;
+
+ /*
+ * Initially, no need to check any further as this entry as well
+ * as following entries have never been used.
+ */
+ if (rt->time == 0)
+ break;
+
+ /* Check if entry expired. */
+ if (time_before(rt->time, invalid_before))
+ continue; /* before KCSAN_REPORT_ONCE_IN_MS ago */
+
+ /* Reported recently, check if race matches. */
+ if ((rt->frame1 == frame1 && rt->frame2 == frame2) ||
+ (rt->frame1 == frame2 && rt->frame2 == frame1))
+ return true;
+ }
+
+ use_entry->time = jiffies;
+ use_entry->frame1 = frame1;
+ use_entry->frame2 = frame2;
+ return false;
+}
+
+/*
+ * Special rules to skip reporting.
+ */
+static bool
+skip_report(enum kcsan_value_change value_change, unsigned long top_frame)
+{
+ /* Should never get here if value_change==FALSE. */
+ WARN_ON_ONCE(value_change == KCSAN_VALUE_CHANGE_FALSE);
+
+ /*
+ * The first call to skip_report always has value_change==TRUE, since we
+ * cannot know the value written of an instrumented access. For the 2nd
+ * call there are 6 cases with CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY:
+ *
+ * 1. read watchpoint, conflicting write (value_change==TRUE): report;
+ * 2. read watchpoint, conflicting write (value_change==MAYBE): skip;
+ * 3. write watchpoint, conflicting write (value_change==TRUE): report;
+ * 4. write watchpoint, conflicting write (value_change==MAYBE): skip;
+ * 5. write watchpoint, conflicting read (value_change==MAYBE): skip;
+ * 6. write watchpoint, conflicting read (value_change==TRUE): report;
+ *
+ * Cases 1-4 are intuitive and expected; case 5 ensures we do not report
+ * data races where the write may have rewritten the same value; case 6
+ * is possible either if the size is larger than what we check value
+ * changes for or the access type is KCSAN_ACCESS_ASSERT.
+ */
+ if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) &&
+ value_change == KCSAN_VALUE_CHANGE_MAYBE) {
+ /*
+ * The access is a write, but the data value did not change.
+ *
+ * We opt-out of this filter for certain functions at request of
+ * maintainers.
+ */
+ char buf[64];
+
+ snprintf(buf, sizeof(buf), "%ps", (void *)top_frame);
+ if (!strnstr(buf, "rcu_", sizeof(buf)) &&
+ !strnstr(buf, "_rcu", sizeof(buf)) &&
+ !strnstr(buf, "_srcu", sizeof(buf)))
+ return true;
+ }
+
+ return kcsan_skip_report_debugfs(top_frame);
+}
+
+static const char *get_access_type(int type)
+{
+ switch (type) {
+ case 0:
+ return "read";
+ case KCSAN_ACCESS_ATOMIC:
+ return "read (marked)";
+ case KCSAN_ACCESS_WRITE:
+ return "write";
+ case KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC:
+ return "write (marked)";
+
+ /*
+ * ASSERT variants:
+ */
+ case KCSAN_ACCESS_ASSERT:
+ case KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_ATOMIC:
+ return "assert no writes";
+ case KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE:
+ case KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC:
+ return "assert no accesses";
+
+ default:
+ BUG();
+ }
+}
+
+static const char *get_bug_type(int type)
+{
+ return (type & KCSAN_ACCESS_ASSERT) != 0 ? "assert: race" : "data-race";
+}
+
+/* Return thread description: in task or interrupt. */
+static const char *get_thread_desc(int task_id)
+{
+ if (task_id != -1) {
+ static char buf[32]; /* safe: protected by report_lock */
+
+ snprintf(buf, sizeof(buf), "task %i", task_id);
+ return buf;
+ }
+ return "interrupt";
+}
+
+/* Helper to skip KCSAN-related functions in stack-trace. */
+static int get_stack_skipnr(unsigned long stack_entries[], int num_entries)
+{
+ char buf[64];
+ int skip = 0;
+
+ for (; skip < num_entries; ++skip) {
+ snprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]);
+ if (!strnstr(buf, "csan_", sizeof(buf)) &&
+ !strnstr(buf, "tsan_", sizeof(buf)) &&
+ !strnstr(buf, "_once_size", sizeof(buf))) {
+ break;
+ }
+ }
+ return skip;
+}
+
+/* Compares symbolized strings of addr1 and addr2. */
+static int sym_strcmp(void *addr1, void *addr2)
+{
+ char buf1[64];
+ char buf2[64];
+
+ snprintf(buf1, sizeof(buf1), "%pS", addr1);
+ snprintf(buf2, sizeof(buf2), "%pS", addr2);
+
+ return strncmp(buf1, buf2, sizeof(buf1));
+}
+
+/*
+ * Returns true if a report was generated, false otherwise.
+ */
+static bool print_report(const volatile void *ptr, size_t size, int access_type,
+ enum kcsan_value_change value_change, int cpu_id,
+ enum kcsan_report_type type)
+{
+ unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 };
+ int num_stack_entries = stack_trace_save(stack_entries, NUM_STACK_ENTRIES, 1);
+ int skipnr = get_stack_skipnr(stack_entries, num_stack_entries);
+ unsigned long this_frame = stack_entries[skipnr];
+ unsigned long other_frame = 0;
+ int other_skipnr = 0; /* silence uninit warnings */
+
+ /*
+ * Must check report filter rules before starting to print.
+ */
+ if (skip_report(KCSAN_VALUE_CHANGE_TRUE, stack_entries[skipnr]))
+ return false;
+
+ if (type == KCSAN_REPORT_RACE_SIGNAL) {
+ other_skipnr = get_stack_skipnr(other_info.stack_entries,
+ other_info.num_stack_entries);
+ other_frame = other_info.stack_entries[other_skipnr];
+
+ /* @value_change is only known for the other thread */
+ if (skip_report(value_change, other_frame))
+ return false;
+ }
+
+ if (rate_limit_report(this_frame, other_frame))
+ return false;
+
+ /* Print report header. */
+ pr_err("==================================================================\n");
+ switch (type) {
+ case KCSAN_REPORT_RACE_SIGNAL: {
+ int cmp;
+
+ /*
+ * Order functions lexographically for consistent bug titles.
+ * Do not print offset of functions to keep title short.
+ */
+ cmp = sym_strcmp((void *)other_frame, (void *)this_frame);
+ pr_err("BUG: KCSAN: %s in %ps / %ps\n",
+ get_bug_type(access_type | other_info.access_type),
+ (void *)(cmp < 0 ? other_frame : this_frame),
+ (void *)(cmp < 0 ? this_frame : other_frame));
+ } break;
+
+ case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN:
+ pr_err("BUG: KCSAN: %s in %pS\n", get_bug_type(access_type),
+ (void *)this_frame);
+ break;
+
+ default:
+ BUG();
+ }
+
+ pr_err("\n");
+
+ /* Print information about the racing accesses. */
+ switch (type) {
+ case KCSAN_REPORT_RACE_SIGNAL:
+ pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
+ get_access_type(other_info.access_type), other_info.ptr,
+ other_info.size, get_thread_desc(other_info.task_pid),
+ other_info.cpu_id);
+
+ /* Print the other thread's stack trace. */
+ stack_trace_print(other_info.stack_entries + other_skipnr,
+ other_info.num_stack_entries - other_skipnr,
+ 0);
+
+ pr_err("\n");
+ pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
+ get_access_type(access_type), ptr, size,
+ get_thread_desc(in_task() ? task_pid_nr(current) : -1),
+ cpu_id);
+ break;
+
+ case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN:
+ pr_err("race at unknown origin, with %s to 0x%px of %zu bytes by %s on cpu %i:\n",
+ get_access_type(access_type), ptr, size,
+ get_thread_desc(in_task() ? task_pid_nr(current) : -1),
+ cpu_id);
+ break;
+
+ default:
+ BUG();
+ }
+ /* Print stack trace of this thread. */
+ stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
+ 0);
+
+ /* Print report footer. */
+ pr_err("\n");
+ pr_err("Reported by Kernel Concurrency Sanitizer on:\n");
+ dump_stack_print_info(KERN_DEFAULT);
+ pr_err("==================================================================\n");
+
+ return true;
+}
+
+static void release_report(unsigned long *flags, enum kcsan_report_type type)
+{
+ if (type == KCSAN_REPORT_RACE_SIGNAL)
+ other_info.ptr = NULL; /* mark for reuse */
+
+ spin_unlock_irqrestore(&report_lock, *flags);
+}
+
+/*
+ * Depending on the report type either sets other_info and returns false, or
+ * acquires the matching other_info and returns true. If other_info is not
+ * required for the report type, simply acquires report_lock and returns true.
+ */
+static bool prepare_report(unsigned long *flags, const volatile void *ptr,
+ size_t size, int access_type, int cpu_id,
+ enum kcsan_report_type type)
+{
+ if (type != KCSAN_REPORT_CONSUMED_WATCHPOINT &&
+ type != KCSAN_REPORT_RACE_SIGNAL) {
+ /* other_info not required; just acquire report_lock */
+ spin_lock_irqsave(&report_lock, *flags);
+ return true;
+ }
+
+retry:
+ spin_lock_irqsave(&report_lock, *flags);
+
+ switch (type) {
+ case KCSAN_REPORT_CONSUMED_WATCHPOINT:
+ if (other_info.ptr != NULL)
+ break; /* still in use, retry */
+
+ other_info.ptr = ptr;
+ other_info.size = size;
+ other_info.access_type = access_type;
+ other_info.task_pid = in_task() ? task_pid_nr(current) : -1;
+ other_info.cpu_id = cpu_id;
+ other_info.num_stack_entries = stack_trace_save(other_info.stack_entries, NUM_STACK_ENTRIES, 1);
+
+ spin_unlock_irqrestore(&report_lock, *flags);
+
+ /*
+ * The other thread will print the summary; other_info may now
+ * be consumed.
+ */
+ return false;
+
+ case KCSAN_REPORT_RACE_SIGNAL:
+ if (other_info.ptr == NULL)
+ break; /* no data available yet, retry */
+
+ /*
+ * First check if this is the other_info we are expecting, i.e.
+ * matches based on how watchpoint was encoded.
+ */
+ if (!matching_access((unsigned long)other_info.ptr &
+ WATCHPOINT_ADDR_MASK,
+ other_info.size,
+ (unsigned long)ptr & WATCHPOINT_ADDR_MASK,
+ size))
+ break; /* mismatching watchpoint, retry */
+
+ if (!matching_access((unsigned long)other_info.ptr,
+ other_info.size, (unsigned long)ptr,
+ size)) {
+ /*
+ * If the actual accesses to not match, this was a false
+ * positive due to watchpoint encoding.
+ */
+ kcsan_counter_inc(
+ KCSAN_COUNTER_ENCODING_FALSE_POSITIVES);
+
+ /* discard this other_info */
+ release_report(flags, KCSAN_REPORT_RACE_SIGNAL);
+ return false;
+ }
+
+ access_type |= other_info.access_type;
+ if ((access_type & KCSAN_ACCESS_WRITE) == 0) {
+ /*
+ * While the address matches, this is not the other_info
+ * from the thread that consumed our watchpoint, since
+ * neither this nor the access in other_info is a write.
+ * It is invalid to continue with the report, since we
+ * only have information about reads.
+ *
+ * This can happen due to concurrent races on the same
+ * address, with at least 4 threads. To avoid locking up
+ * other_info and all other threads, we have to consume
+ * it regardless.
+ *
+ * A concrete case to illustrate why we might lock up if
+ * we do not consume other_info:
+ *
+ * We have 4 threads, all accessing the same address
+ * (or matching address ranges). Assume the following
+ * watcher and watchpoint consumer pairs:
+ * write1-read1, read2-write2. The first to populate
+ * other_info is write2, however, write1 consumes it,
+ * resulting in a report of write1-write2. This report
+ * is valid, however, now read1 populates other_info;
+ * read2-read1 is an invalid conflict, yet, no other
+ * conflicting access is left. Therefore, we must
+ * consume read1's other_info.
+ *
+ * Since this case is assumed to be rare, it is
+ * reasonable to omit this report: one of the other
+ * reports includes information about the same shared
+ * data, and at this point the likelihood that we
+ * re-report the same race again is high.
+ */
+ release_report(flags, KCSAN_REPORT_RACE_SIGNAL);
+ return false;
+ }
+
+ /*
+ * Matching & usable access in other_info: keep other_info_lock
+ * locked, as this thread consumes it to print the full report;
+ * unlocked in release_report.
+ */
+ return true;
+
+ default:
+ BUG();
+ }
+
+ spin_unlock_irqrestore(&report_lock, *flags);
+
+ goto retry;
+}
+
+void kcsan_report(const volatile void *ptr, size_t size, int access_type,
+ enum kcsan_value_change value_change, int cpu_id,
+ enum kcsan_report_type type)
+{
+ unsigned long flags = 0;
+
+ /*
+ * With TRACE_IRQFLAGS, lockdep's IRQ trace state becomes corrupted if
+ * we do not turn off lockdep here; this could happen due to recursion
+ * into lockdep via KCSAN if we detect a race in utilities used by
+ * lockdep.
+ */
+ lockdep_off();
+
+ kcsan_disable_current();
+ if (prepare_report(&flags, ptr, size, access_type, cpu_id, type)) {
+ /*
+ * Never report if value_change is FALSE, only if we it is
+ * either TRUE or MAYBE. In case of MAYBE, further filtering may
+ * be done once we know the full stack trace in print_report().
+ */
+ bool reported = value_change != KCSAN_VALUE_CHANGE_FALSE &&
+ print_report(ptr, size, access_type, value_change, cpu_id, type);
+
+ if (reported && panic_on_warn)
+ panic("panic_on_warn set ...\n");
+
+ release_report(&flags, type);
+ }
+ kcsan_enable_current();
+
+ lockdep_on();
+}
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