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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Wed, 31 Aug 2022 12:37:14 +0200
Message-ID: <CACT4Y+ZX3U1=cAPXPhoOy6xrngSCfSmyFagXK-9fWtWWODfsew@mail.gmail.com>
Subject: Re: [RFC PATCH 22/30] Code tagging based fault injection
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     akpm@linux-foundation.org, kent.overstreet@linux.dev,
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On Tue, 30 Aug 2022 at 23:50, Suren Baghdasaryan <surenb@google.com> wrote:
>
> 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;

Hi Suren,

If this is going to be used by mainline kernel, it would be good to
integrate this with fail_nth systematic fault injection:
https://elixir.bootlin.com/linux/latest/source/lib/fault-inject.c#L109

Otherwise these dynamic sites won't be tested by testing systems doing
systematic fault injection testing.


> 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
>