[RFC PATCH 22/30] Code tagging based fault injection

Suren Baghdasaryan
2022-08-30T21:53:33Z

From: Kent Overstreet <kent.overstreet@linux.dev>

This adds a new fault injection capability, based on code tagging.

To use, simply insert somewhere in your code

dynamic_fault("fault_class_name")

and check whether it returns true - if so, inject the error.
For example

if (dynamic_fault("init"))
return -EINVAL;

There's no need to define faults elsewhere, as with
include/linux/fault-injection.h. Faults show up in debugfs, under
/sys/kernel/debug/dynamic_faults, and can be selected based on
file/module/function/line number/class, and enabled permanently, or in
oneshot mode, or with a specified frequency.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
---
include/asm-generic/codetag.lds.h | 3 +-
include/linux/dynamic_fault.h | 79 +++++++
include/linux/slab.h | 3 +-
lib/Kconfig.debug | 6 +
lib/Makefile | 2 +
lib/dynamic_fault.c | 372 ++++++++++++++++++++++++++++++
6 files changed, 463 insertions(+), 2 deletions(-)
create mode 100644 include/linux/dynamic_fault.h
create mode 100644 lib/dynamic_fault.c

diff --git a/include/asm-generic/codetag.lds.h b/include/asm-generic/codetag.lds.h
index 64f536b80380..16fbf74edc3d 100644
--- a/include/asm-generic/codetag.lds.h
+++ b/include/asm-generic/codetag.lds.h
@@ -9,6 +9,7 @@
__stop_##_name = .;

#define CODETAG_SECTIONS() \
- SECTION_WITH_BOUNDARIES(alloc_tags)
+ SECTION_WITH_BOUNDARIES(alloc_tags) \
+ SECTION_WITH_BOUNDARIES(dynamic_fault_tags)

#endif /* __ASM_GENERIC_CODETAG_LDS_H */
diff --git a/include/linux/dynamic_fault.h b/include/linux/dynamic_fault.h
new file mode 100644
index 000000000000..526a33209e94
--- /dev/null
+++ b/include/linux/dynamic_fault.h
@@ -0,0 +1,79 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_DYNAMIC_FAULT_H
+#define _LINUX_DYNAMIC_FAULT_H
+
+/*
+ * Dynamic/code tagging fault injection:
+ *
+ * Originally based on the dynamic debug trick of putting types in a special elf
+ * section, then rewritten using code tagging:
+ *
+ * To use, simply insert a call to dynamic_fault("fault_class"), which will
+ * return true if an error should be injected.
+ *
+ * Fault injection sites may be listed and enabled via debugfs, under
+ * /sys/kernel/debug/dynamic_faults.
+ */
+
+#ifdef CONFIG_CODETAG_FAULT_INJECTION
+
+#include <linux/codetag.h>
+#include <linux/jump_label.h>
+
+#define DFAULT_STATES() \
+ x(disabled) \
+ x(enabled) \
+ x(oneshot)
+
+enum dfault_enabled {
+#define x(n) DFAULT_##n,
+ DFAULT_STATES()
+#undef x
+};
+
+union dfault_state {
+ struct {
+ unsigned int enabled:2;
+ unsigned int count:30;
+ };
+
+ struct {
+ unsigned int v;
+ };
+};
+
+struct dfault {
+ struct codetag tag;
+ const char *class;
+ unsigned int frequency;
+ union dfault_state state;
+ struct static_key_false enabled;
+};
+
+bool __dynamic_fault_enabled(struct dfault *df);
+
+#define dynamic_fault(_class) \
+({ \
+ static struct dfault \
+ __used \
+ __section("dynamic_fault_tags") \
+ __aligned(8) df = { \
+ .tag = CODE_TAG_INIT, \
+ .class = _class, \
+ .enabled = STATIC_KEY_FALSE_INIT, \
+ }; \
+ \
+ static_key_false(&df.enabled.key) && \
+ __dynamic_fault_enabled(&df); \
+})
+
+#else
+
+#define dynamic_fault(_class) false
+
+#endif /* CODETAG_FAULT_INJECTION */
+
+#define memory_fault() dynamic_fault("memory")
+
+#endif /* _LINUX_DYNAMIC_FAULT_H */
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 89273be35743..4be5a93ed15a 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -17,6 +17,7 @@
#include <linux/types.h>
#include <linux/workqueue.h>
#include <linux/percpu-refcount.h>
+#include <linux/dynamic_fault.h>

/*
@@ -468,7 +469,7 @@ static inline void slab_tag_dec(const void *ptr) {}

#define krealloc_hooks(_p, _do_alloc) \
({ \
- void *_res = _do_alloc; \
+ void *_res = !memory_fault() ? _do_alloc : NULL; \
slab_tag_add(_p, _res); \
_res; \
})
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 2790848464f1..b7d03afbc808 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1982,6 +1982,12 @@ config FAULT_INJECTION_STACKTRACE_FILTER
help
Provide stacktrace filter for fault-injection capabilities

+config CODETAG_FAULT_INJECTION
+ bool "Code tagging based fault injection"
+ select CODE_TAGGING
+ help
+ Dynamic fault injection based on code tagging
+
config ARCH_HAS_KCOV
bool
help
diff --git a/lib/Makefile b/lib/Makefile
index 99f732156673..489ea000c528 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -231,6 +231,8 @@ obj-$(CONFIG_CODE_TAGGING) += codetag.o
obj-$(CONFIG_ALLOC_TAGGING) += alloc_tag.o
obj-$(CONFIG_PAGE_ALLOC_TAGGING) += pgalloc_tag.o

+obj-$(CONFIG_CODETAG_FAULT_INJECTION) += dynamic_fault.o
+
lib-$(CONFIG_GENERIC_BUG) += bug.o

obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o
diff --git a/lib/dynamic_fault.c b/lib/dynamic_fault.c
new file mode 100644
index 000000000000..4c9cd18686be
--- /dev/null
+++ b/lib/dynamic_fault.c
@@ -0,0 +1,372 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/ctype.h>
+#include <linux/debugfs.h>
+#include <linux/dynamic_fault.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/seq_buf.h>
+
+static struct codetag_type *cttype;
+
+bool __dynamic_fault_enabled(struct dfault *df)
+{
+ union dfault_state old, new;
+ unsigned int v = df->state.v;
+ bool ret;
+
+ do {
+ old.v = new.v = v;
+
+ if (new.enabled == DFAULT_disabled)
+ return false;
+
+ ret = df->frequency
+ ? ++new.count >= df->frequency
+ : true;
+ if (ret)
+ new.count = 0;
+ if (ret && new.enabled == DFAULT_oneshot)
+ new.enabled = DFAULT_disabled;
+ } while ((v = cmpxchg(&df->state.v, old.v, new.v)) != old.v);
+
+ if (ret)
+ pr_debug("returned true for %s:%u", df->tag.filename, df->tag.lineno);
+
+ return ret;
+}
+EXPORT_SYMBOL(__dynamic_fault_enabled);
+
+static const char * const dfault_state_strs[] = {
+#define x(n) #n,
+ DFAULT_STATES()
+#undef x
+ NULL
+};
+
+static void dynamic_fault_to_text(struct seq_buf *out, struct dfault *df)
+{
+ codetag_to_text(out, &df->tag);
+ seq_buf_printf(out, "class:%s %s \"", df->class,
+ dfault_state_strs[df->state.enabled]);
+}
+
+struct dfault_query {
+ struct codetag_query q;
+
+ bool set_enabled:1;
+ unsigned int enabled:2;
+
+ bool set_frequency:1;
+ unsigned int frequency;
+};
+
+/*
+ * Search the tables for _dfault's which match the given
+ * `query' and apply the `flags' and `mask' to them. Tells
+ * the user which dfault's were changed, or whether none
+ * were matched.
+ */
+static int dfault_change(struct dfault_query *query)
+{
+ struct codetag_iterator ct_iter;
+ struct codetag *ct;
+ unsigned int nfound = 0;
+
+ codetag_lock_module_list(cttype, true);
+ codetag_init_iter(&ct_iter, cttype);
+
+ while ((ct = codetag_next_ct(&ct_iter))) {
+ struct dfault *df = container_of(ct, struct dfault, tag);
+
+ if (!codetag_matches_query(&query->q, ct, ct_iter.cmod, df->class))
+ continue;
+
+ if (query->set_enabled &&
+ query->enabled != df->state.enabled) {
+ if (query->enabled != DFAULT_disabled)
+ static_key_slow_inc(&df->enabled.key);
+ else if (df->state.enabled != DFAULT_disabled)
+ static_key_slow_dec(&df->enabled.key);
+
+ df->state.enabled = query->enabled;
+ }
+
+ if (query->set_frequency)
+ df->frequency = query->frequency;
+
+ pr_debug("changed %s:%d [%s]%s #%d %s",
+ df->tag.filename, df->tag.lineno, df->tag.modname,
+ df->tag.function, query->q.cur_index,
+ dfault_state_strs[df->state.enabled]);
+
+ nfound++;
+ }
+
+ pr_debug("dfault: %u matches", nfound);
+
+ codetag_lock_module_list(cttype, false);
+
+ return nfound ? 0 : -ENOENT;
+}
+
+#define DFAULT_TOKENS() \
+ x(disable, 0) \
+ x(enable, 0) \
+ x(oneshot, 0) \
+ x(frequency, 1)
+
+enum dfault_token {
+#define x(name, nr_args) TOK_##name,
+ DFAULT_TOKENS()
+#undef x
+};
+
+static const char * const dfault_token_strs[] = {
+#define x(name, nr_args) #name,
+ DFAULT_TOKENS()
+#undef x
+ NULL
+};
+
+static unsigned int dfault_token_nr_args[] = {
+#define x(name, nr_args) nr_args,
+ DFAULT_TOKENS()
+#undef x
+};
+
+static enum dfault_token str_to_token(const char *word, unsigned int nr_words)
+{
+ int tok = match_string(dfault_token_strs, ARRAY_SIZE(dfault_token_strs), word);
+
+ if (tok < 0) {
+ pr_debug("unknown keyword \"%s\"", word);
+ return tok;
+ }
+
+ if (nr_words < dfault_token_nr_args[tok]) {
+ pr_debug("insufficient arguments to \"%s\"", word);
+ return -EINVAL;
+ }
+
+ return tok;
+}
+
+static int dfault_parse_command(struct dfault_query *query,
+ enum dfault_token tok,
+ char *words[], size_t nr_words)
+{
+ unsigned int i = 0;
+ int ret;
+
+ switch (tok) {
+ case TOK_disable:
+ query->set_enabled = true;
+ query->enabled = DFAULT_disabled;
+ break;
+ case TOK_enable:
+ query->set_enabled = true;
+ query->enabled = DFAULT_enabled;
+ break;
+ case TOK_oneshot:
+ query->set_enabled = true;
+ query->enabled = DFAULT_oneshot;
+ break;
+ case TOK_frequency:
+ query->set_frequency = 1;
+ ret = kstrtouint(words[i++], 10, &query->frequency);
+ if (ret)
+ return ret;
+
+ if (!query->set_enabled) {
+ query->set_enabled = 1;
+ query->enabled = DFAULT_enabled;
+ }
+ break;
+ }
+
+ return i;
+}
+
+static int dynamic_fault_store(char *buf)
+{
+ struct dfault_query query = { NULL };
+#define MAXWORDS 9
+ char *tok, *words[MAXWORDS];
+ int ret, nr_words, i = 0;
+
+ buf = codetag_query_parse(&query.q, buf);
+ if (IS_ERR(buf))
+ return PTR_ERR(buf);
+
+ while ((tok = strsep_no_empty(&buf, " \t\r\n"))) {
+ if (nr_words == ARRAY_SIZE(words))
+ return -EINVAL; /* ran out of words[] before bytes */
+ words[nr_words++] = tok;
+ }
+
+ while (i < nr_words) {
+ const char *tok_str = words[i++];
+ enum dfault_token tok = str_to_token(tok_str, nr_words - i);
+
+ if (tok < 0)
+ return tok;
+
+ ret = dfault_parse_command(&query, tok, words + i, nr_words - i);
+ if (ret < 0)
+ return ret;
+
+ i += ret;
+ BUG_ON(i > nr_words);
+ }
+
+ pr_debug("q->function=\"%s\" q->filename=\"%s\" "
+ "q->module=\"%s\" q->line=%u-%u\n q->index=%u-%u",
+ query.q.function, query.q.filename, query.q.module,
+ query.q.first_line, query.q.last_line,
+ query.q.first_index, query.q.last_index);
+
+ ret = dfault_change(&query);
+ if (ret < 0)
+ return ret;
+
+ return 0;
+}
+
+struct dfault_iter {
+ struct codetag_iterator ct_iter;
+
+ struct seq_buf buf;
+ char rawbuf[4096];
+};
+
+static int dfault_open(struct inode *inode, struct file *file)
+{
+ struct dfault_iter *iter;
+
+ iter = kzalloc(sizeof(*iter), GFP_KERNEL);
+ if (!iter)
+ return -ENOMEM;
+
+ codetag_lock_module_list(cttype, true);
+ codetag_init_iter(&iter->ct_iter, cttype);
+ codetag_lock_module_list(cttype, false);
+
+ file->private_data = iter;
+ seq_buf_init(&iter->buf, iter->rawbuf, sizeof(iter->rawbuf));
+ return 0;
+}
+
+static int dfault_release(struct inode *inode, struct file *file)
+{
+ struct dfault_iter *iter = file->private_data;
+
+ kfree(iter);
+ return 0;
+}
+
+struct user_buf {
+ char __user *buf; /* destination user buffer */
+ size_t size; /* size of requested read */
+ ssize_t ret; /* bytes read so far */
+};
+
+static int flush_ubuf(struct user_buf *dst, struct seq_buf *src)
+{
+ if (src->len) {
+ size_t bytes = min_t(size_t, src->len, dst->size);
+ int err = copy_to_user(dst->buf, src->buffer, bytes);
+
+ if (err)
+ return err;
+
+ dst->ret += bytes;
+ dst->buf += bytes;
+ dst->size -= bytes;
+ src->len -= bytes;
+ memmove(src->buffer, src->buffer + bytes, src->len);
+ }
+
+ return 0;
+}
+
+static ssize_t dfault_read(struct file *file, char __user *ubuf,
+ size_t size, loff_t *ppos)
+{
+ struct dfault_iter *iter = file->private_data;
+ struct user_buf buf = { .buf = ubuf, .size = size };
+ struct codetag *ct;
+ struct dfault *df;
+ int err;
+
+ codetag_lock_module_list(iter->ct_iter.cttype, true);
+ while (1) {
+ err = flush_ubuf(&buf, &iter->buf);
+ if (err || !buf.size)
+ break;
+
+ ct = codetag_next_ct(&iter->ct_iter);
+ if (!ct)
+ break;
+
+ df = container_of(ct, struct dfault, tag);
+ dynamic_fault_to_text(&iter->buf, df);
+ seq_buf_putc(&iter->buf, '\n');
+ }
+ codetag_lock_module_list(iter->ct_iter.cttype, false);
+
+ return err ?: buf.ret;
+}
+
+/*
+ * File_ops->write method for <debugfs>/dynamic_fault/conrol. Gathers the
+ * command text from userspace, parses and executes it.
+ */
+static ssize_t dfault_write(struct file *file, const char __user *ubuf,
+ size_t len, loff_t *offp)
+{
+ char tmpbuf[256];
+
+ if (len == 0)
+ return 0;
+ /* we don't check *offp -- multiple writes() are allowed */
+ if (len > sizeof(tmpbuf)-1)
+ return -E2BIG;
+ if (copy_from_user(tmpbuf, ubuf, len))
+ return -EFAULT;
+ tmpbuf[len] = '\0';
+ pr_debug("read %zu bytes from userspace", len);
+
+ dynamic_fault_store(tmpbuf);
+
+ *offp += len;
+ return len;
+}
+
+static const struct file_operations dfault_ops = {
+ .owner = THIS_MODULE,
+ .open = dfault_open,
+ .release = dfault_release,
+ .read = dfault_read,
+ .write = dfault_write
+};
+
+static int __init dynamic_fault_init(void)
+{
+ const struct codetag_type_desc desc = {
+ .section = "dynamic_fault_tags",
+ .tag_size = sizeof(struct dfault),
+ };
+ struct dentry *debugfs_file;
+
+ cttype = codetag_register_type(&desc);
+ if (IS_ERR_OR_NULL(cttype))
+ return PTR_ERR(cttype);
+
+ debugfs_file = debugfs_create_file("dynamic_faults", 0666, NULL, NULL, &dfault_ops);
+ if (IS_ERR(debugfs_file))
+ return PTR_ERR(debugfs_file);
+
+ return 0;
+}
+module_init(dynamic_fault_init);
--
2.37.2.672.g94769d06f0-goog