Re: [PATCH v3 10/35] lib: code tagging framework

Kees Cook
2024-02-12T22:27:15Z

On Mon, Feb 12, 2024 at 01:38:56PM -0800, Suren Baghdasaryan wrote:
> Add basic infrastructure to support code tagging which stores tag common
> information consisting of the module name, function, file name and line
> number. Provide functions to register a new code tag type and navigate
> between code tags.
>
> Co-developed-by: Kent Overstreet <kent.overstreet@linux.dev>
> Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
> include/linux/codetag.h | 71 ++++++++++++++
> lib/Kconfig.debug | 4 +
> lib/Makefile | 1 +
> lib/codetag.c | 199 ++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 275 insertions(+)
> create mode 100644 include/linux/codetag.h
> create mode 100644 lib/codetag.c
>
> diff --git a/include/linux/codetag.h b/include/linux/codetag.h
> new file mode 100644
> index 000000000000..a9d7adecc2a5
> --- /dev/null
> +++ b/include/linux/codetag.h
> @@ -0,0 +1,71 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * code tagging framework
> + */
> +#ifndef _LINUX_CODETAG_H
> +#define _LINUX_CODETAG_H
> +
> +#include <linux/types.h>
> +
> +struct codetag_iterator;
> +struct codetag_type;
> +struct seq_buf;
> +struct module;
> +
> +/*
> + * An instance of this structure is created in a special ELF section at every
> + * code location being tagged. At runtime, the special section is treated as
> + * an array of these.
> + */
> +struct codetag {
> + unsigned int flags; /* used in later patches */
> + unsigned int lineno;
> + const char *modname;
> + const char *function;
> + const char *filename;
> +} __aligned(8);
> +
> +union codetag_ref {
> + struct codetag *ct;
> +};
> +
> +struct codetag_range {
> + struct codetag *start;
> + struct codetag *stop;
> +};
> +
> +struct codetag_module {
> + struct module *mod;
> + struct codetag_range range;
> +};
> +
> +struct codetag_type_desc {
> + const char *section;
> + size_t tag_size;
> +};
> +
> +struct codetag_iterator {
> + struct codetag_type *cttype;
> + struct codetag_module *cmod;
> + unsigned long mod_id;
> + struct codetag *ct;
> +};
> +
> +#define CODE_TAG_INIT { \
> + .modname = KBUILD_MODNAME, \
> + .function = __func__, \
> + .filename = __FILE__, \
> + .lineno = __LINE__, \
> + .flags = 0, \
> +}
> +
> +void codetag_lock_module_list(struct codetag_type *cttype, bool lock);
> +struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype);
> +struct codetag *codetag_next_ct(struct codetag_iterator *iter);
> +
> +void codetag_to_text(struct seq_buf *out, struct codetag *ct);
> +
> +struct codetag_type *
> +codetag_register_type(const struct codetag_type_desc *desc);
> +
> +#endif /* _LINUX_CODETAG_H */
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 975a07f9f1cc..0be2d00c3696 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -968,6 +968,10 @@ config DEBUG_STACKOVERFLOW
>
> If in doubt, say "N".
>
> +config CODE_TAGGING
> + bool
> + select KALLSYMS
> +
> source "lib/Kconfig.kasan"
> source "lib/Kconfig.kfence"
> source "lib/Kconfig.kmsan"
> diff --git a/lib/Makefile b/lib/Makefile
> index 6b09731d8e61..6b48b22fdfac 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -235,6 +235,7 @@ obj-$(CONFIG_OF_RECONFIG_NOTIFIER_ERROR_INJECT) += \
> of-reconfig-notifier-error-inject.o
> obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
>
> +obj-$(CONFIG_CODE_TAGGING) += codetag.o
> lib-$(CONFIG_GENERIC_BUG) += bug.o
>
> obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o
> diff --git a/lib/codetag.c b/lib/codetag.c
> new file mode 100644
> index 000000000000..7708f8388e55
> --- /dev/null
> +++ b/lib/codetag.c
> @@ -0,0 +1,199 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include <linux/codetag.h>
> +#include <linux/idr.h>
> +#include <linux/kallsyms.h>
> +#include <linux/module.h>
> +#include <linux/seq_buf.h>
> +#include <linux/slab.h>
> +
> +struct codetag_type {
> + struct list_head link;
> + unsigned int count;
> + struct idr mod_idr;
> + struct rw_semaphore mod_lock; /* protects mod_idr */
> + struct codetag_type_desc desc;
> +};
> +
> +static DEFINE_MUTEX(codetag_lock);
> +static LIST_HEAD(codetag_types);
> +
> +void codetag_lock_module_list(struct codetag_type *cttype, bool lock)
> +{
> + if (lock)
> + down_read(&cttype->mod_lock);
> + else
> + up_read(&cttype->mod_lock);
> +}
> +
> +struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype)
> +{
> + struct codetag_iterator iter = {
> + .cttype = cttype,
> + .cmod = NULL,
> + .mod_id = 0,
> + .ct = NULL,
> + };
> +
> + return iter;
> +}
> +
> +static inline struct codetag *get_first_module_ct(struct codetag_module *cmod)
> +{
> + return cmod->range.start < cmod->range.stop ? cmod->range.start : NULL;
> +}
> +
> +static inline
> +struct codetag *get_next_module_ct(struct codetag_iterator *iter)
> +{
> + struct codetag *res = (struct codetag *)
> + ((char *)iter->ct + iter->cttype->desc.tag_size);
> +
> + return res < iter->cmod->range.stop ? res : NULL;
> +}
> +
> +struct codetag *codetag_next_ct(struct codetag_iterator *iter)
> +{
> + struct codetag_type *cttype = iter->cttype;
> + struct codetag_module *cmod;
> + struct codetag *ct;
> +
> + lockdep_assert_held(&cttype->mod_lock);
> +
> + if (unlikely(idr_is_empty(&cttype->mod_idr)))
> + return NULL;
> +
> + ct = NULL;
> + while (true) {
> + cmod = idr_find(&cttype->mod_idr, iter->mod_id);
> +
> + /* If module was removed move to the next one */
> + if (!cmod)
> + cmod = idr_get_next_ul(&cttype->mod_idr,
> + &iter->mod_id);
> +
> + /* Exit if no more modules */
> + if (!cmod)
> + break;
> +
> + if (cmod != iter->cmod) {
> + iter->cmod = cmod;
> + ct = get_first_module_ct(cmod);
> + } else
> + ct = get_next_module_ct(iter);
> +
> + if (ct)
> + break;
> +
> + iter->mod_id++;
> + }
> +
> + iter->ct = ct;
> + return ct;
> +}
> +
> +void codetag_to_text(struct seq_buf *out, struct codetag *ct)
> +{
> + seq_buf_printf(out, "%s:%u module:%s func:%s",
> + ct->filename, ct->lineno,
> + ct->modname, ct->function);
> +}

Thank you for using seq_buf here!

Also, will this need an EXPORT_SYMBOL_GPL()?

> +
> +static inline size_t range_size(const struct codetag_type *cttype,
> + const struct codetag_range *range)
> +{
> + return ((char *)range->stop - (char *)range->start) /
> + cttype->desc.tag_size;
> +}
> +
> +static void *get_symbol(struct module *mod, const char *prefix, const char *name)
> +{
> + char buf[64];

Why is 64 enough? I was expecting KSYM_NAME_LEN here, but perhaps this
is specialized enough to section names that it will not be a problem?
If so, please document it clearly with a comment.

> + int res;
> +
> + res = snprintf(buf, sizeof(buf), "%s%s", prefix, name);
> + if (WARN_ON(res < 1 || res > sizeof(buf)))
> + return NULL;

Please use a seq_buf here instead of snprintf, which we're trying to get
rid of.

DECLARE_SEQ_BUF(sb, KSYM_NAME_LEN);
char *buf;

seq_buf_printf(sb, "%s%s", prefix, name);
if (seq_buf_has_overflowed(sb))
return NULL;

buf = seq_buf_str(sb);

> +
> + return mod ?
> + (void *)find_kallsyms_symbol_value(mod, buf) :
> + (void *)kallsyms_lookup_name(buf);
> +}
> +
> +static struct codetag_range get_section_range(struct module *mod,
> + const char *section)
> +{
> + return (struct codetag_range) {
> + get_symbol(mod, "__start_", section),
> + get_symbol(mod, "__stop_", section),
> + };
> +}
> +
> +static int codetag_module_init(struct codetag_type *cttype, struct module *mod)
> +{
> + struct codetag_range range;
> + struct codetag_module *cmod;
> + int err;
> +
> + range = get_section_range(mod, cttype->desc.section);
> + if (!range.start || !range.stop) {
> + pr_warn("Failed to load code tags of type %s from the module %s\n",
> + cttype->desc.section,
> + mod ? mod->name : "(built-in)");
> + return -EINVAL;
> + }
> +
> + /* Ignore empty ranges */
> + if (range.start == range.stop)
> + return 0;
> +
> + BUG_ON(range.start > range.stop);
> +
> + cmod = kmalloc(sizeof(*cmod), GFP_KERNEL);
> + if (unlikely(!cmod))
> + return -ENOMEM;
> +
> + cmod->mod = mod;
> + cmod->range = range;
> +
> + down_write(&cttype->mod_lock);
> + err = idr_alloc(&cttype->mod_idr, cmod, 0, 0, GFP_KERNEL);
> + if (err >= 0)
> + cttype->count += range_size(cttype, &range);
> + up_write(&cttype->mod_lock);
> +
> + if (err < 0) {
> + kfree(cmod);
> + return err;
> + }
> +
> + return 0;
> +}
> +
> +struct codetag_type *
> +codetag_register_type(const struct codetag_type_desc *desc)
> +{
> + struct codetag_type *cttype;
> + int err;
> +
> + BUG_ON(desc->tag_size <= 0);
> +
> + cttype = kzalloc(sizeof(*cttype), GFP_KERNEL);
> + if (unlikely(!cttype))
> + return ERR_PTR(-ENOMEM);
> +
> + cttype->desc = *desc;
> + idr_init(&cttype->mod_idr);
> + init_rwsem(&cttype->mod_lock);
> +
> + err = codetag_module_init(cttype, NULL);
> + if (unlikely(err)) {
> + kfree(cttype);
> + return ERR_PTR(err);
> + }
> +
> + mutex_lock(&codetag_lock);
> + list_add_tail(&cttype->link, &codetag_types);
> + mutex_unlock(&codetag_lock);
> +
> + return cttype;
> +}
> --
> 2.43.0.687.g38aa6559b0-goog
>

--
Kees Cook