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Subject: [RFC PATCH 22/30] Code tagging based fault injection
From:   Suren Baghdasaryan <surenb@google.com>
To:     akpm@linux-foundation.org
Cc:     kent.overstreet@linux.dev, mhocko@suse.com, vbabka@suse.cz,
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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