Re: [PATCH 3/3] pstore: add 'rmmod ramoops' support

[Kees Cook]

On Fri, Oct 16, 2015 at 8:25 AM, Geliang Tang <geliangtang@xxxxxxx> wrote:
> ramoops doesn't support unregistering yet, it was marked as TODO.
> This patch adds some code to fix it:
>  1) Add functions to unregister kmsg/console/ftrace/pmsg.
>  2) Add a function to free compression buffer.
>  3) Remove try_module_get() to allow this module can be unloaded.
>  4) Unmap the memory and free it.
>  5) Set console flags, make sure it can be registered again after
> be unregistered.
>
> Signed-off-by: Geliang Tang <geliangtang@xxxxxxx>
> ---
>  fs/pstore/ftrace.c     | 15 ++++++++++++++-
>  fs/pstore/internal.h   |  4 ++++
>  fs/pstore/platform.c   | 40 ++++++++++++++++++++++++++++++++--------
>  fs/pstore/pmsg.c       |  7 +++++++
>  fs/pstore/ram.c        | 19 ++++++++-----------
>  include/linux/pstore.h |  5 +++++
>  6 files changed, 70 insertions(+), 20 deletions(-)
>
> diff --git a/fs/pstore/ftrace.c b/fs/pstore/ftrace.c
> index 76a4eeb..554c1ce 100644
> --- a/fs/pstore/ftrace.c
> +++ b/fs/pstore/ftrace.c
> @@ -104,9 +104,10 @@ static const struct file_operations pstore_knob_fops = {
>         .write  = pstore_ftrace_knob_write,
>  };
>
> +static struct dentry *dir;

Since this is no longer a local, it should probably be renamed
something more descriptive.

> +
>  void pstore_register_ftrace(void)
>  {
> -       struct dentry *dir;
>         struct dentry *file;
>
>         if (!psinfo->write_buf)
> @@ -129,3 +130,15 @@ void pstore_register_ftrace(void)
>  err_file:
>         debugfs_remove(dir);
>  }
> +
> +void pstore_unregister_ftrace(void)
> +{
> +       mutex_lock(&pstore_ftrace_lock);
> +       if (pstore_ftrace_enabled) {
> +               unregister_ftrace_function(&pstore_ftrace_ops);
> +               pstore_ftrace_enabled = 0;
> +       }
> +       mutex_unlock(&pstore_ftrace_lock);
> +
> +       debugfs_remove_recursive(dir);
> +}
> diff --git a/fs/pstore/internal.h b/fs/pstore/internal.h
> index c36ba2c..96253c4 100644
> --- a/fs/pstore/internal.h
> +++ b/fs/pstore/internal.h
> @@ -41,14 +41,18 @@ pstore_ftrace_decode_cpu(struct pstore_ftrace_record *rec)
>
>  #ifdef CONFIG_PSTORE_FTRACE
>  extern void pstore_register_ftrace(void);
> +extern void pstore_unregister_ftrace(void);
>  #else
>  static inline void pstore_register_ftrace(void) {}
> +static inline void pstore_unregister_ftrace(void) {}
>  #endif
>
>  #ifdef CONFIG_PSTORE_PMSG
>  extern void pstore_register_pmsg(void);
> +extern void pstore_unregister_pmsg(void);
>  #else
>  static inline void pstore_register_pmsg(void) {}
> +static inline void pstore_unregister_pmsg(void) {}
>  #endif
>
>  extern struct pstore_info *psinfo;
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index 1b11249..c474dc2 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -237,6 +237,12 @@ static void allocate_buf_for_compression(void)
>
>  }
>
> +static void free_buf_for_compression(void)
> +{
> +       kfree(stream.workspace);
> +       kfree(big_oops_buf);

I think both of these should be set to NULL after their kfrees.

> +}
> +
>  /*
>   * Called when compression fails, since the printk buffer
>   * would be fetched for compression calling it again when
> @@ -358,6 +364,11 @@ static void pstore_register_kmsg(void)
>         kmsg_dump_register(&pstore_dumper);
>  }
>
> +static void pstore_unregister_kmsg(void)
> +{
> +       kmsg_dump_unregister(&pstore_dumper);
> +}
> +
>  #ifdef CONFIG_PSTORE_CONSOLE
>  static void pstore_console_write(struct console *con, const char *s, unsigned c)
>  {
> @@ -387,16 +398,22 @@ static void pstore_console_write(struct console *con, const char *s, unsigned c)
>  static struct console pstore_console = {
>         .name   = "pstore",
>         .write  = pstore_console_write,
> -       .flags  = CON_PRINTBUFFER | CON_ENABLED | CON_ANYTIME,
>         .index  = -1,
>  };
>
>  static void pstore_register_console(void)
>  {
> +       pstore_console.flags = CON_PRINTBUFFER | CON_ENABLED | CON_ANYTIME;

Why do these flags need to move here?

>         register_console(&pstore_console);
>  }
> +
> +static void pstore_unregister_console(void)
> +{
> +       unregister_console(&pstore_console);
> +}
>  #else
>  static void pstore_register_console(void) {}
> +static void pstore_unregister_console(void) {}
>  #endif
>
>  static int pstore_write_compat(enum pstore_type_id type,
> @@ -420,8 +437,6 @@ static int pstore_write_compat(enum pstore_type_id type,
>   */
>  int pstore_register(struct pstore_info *psi)
>  {
> -       struct module *owner = psi->owner;
> -
>         if (backend && strcmp(backend, psi->name))
>                 return -EPERM;
>
> @@ -437,11 +452,6 @@ int pstore_register(struct pstore_info *psi)
>         mutex_init(&psinfo->read_mutex);
>         spin_unlock(&pstore_lock);
>
> -       if (owner && !try_module_get(owner)) {
> -               psinfo = NULL;
> -               return -EINVAL;
> -       }

Don't we still need to hold a module reference?

> -
>         allocate_buf_for_compression();
>
>         if (pstore_is_mounted())
> @@ -473,6 +483,20 @@ int pstore_register(struct pstore_info *psi)
>  }
>  EXPORT_SYMBOL_GPL(pstore_register);
>
> +void pstore_unregister(void)
> +{
> +       pstore_unregister_pmsg();
> +       pstore_unregister_ftrace();
> +       pstore_unregister_console();
> +       pstore_unregister_kmsg();
> +
> +       free_buf_for_compression();
> +
> +       psinfo = NULL;
> +       backend = NULL;
> +}
> +EXPORT_SYMBOL_GPL(pstore_unregister);
> +
>  /*
>   * Read all the records from the persistent store. Create
>   * files in our filesystem.  Don't warn about -EEXIST errors
> diff --git a/fs/pstore/pmsg.c b/fs/pstore/pmsg.c
> index 5a2f05a..7de20cd 100644
> --- a/fs/pstore/pmsg.c
> +++ b/fs/pstore/pmsg.c
> @@ -114,3 +114,10 @@ err_class:
>  err:
>         return;
>  }
> +
> +void pstore_unregister_pmsg(void)
> +{
> +       device_destroy(pmsg_class, MKDEV(pmsg_major, 0));
> +       class_destroy(pmsg_class);
> +       unregister_chrdev(pmsg_major, PMSG_NAME);
> +}
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index 6c26c4d..d938bc1 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -580,28 +580,25 @@ fail_out:
>
>  static int __exit ramoops_remove(struct platform_device *pdev)
>  {
> -#if 0
> -       /* TODO(kees): We cannot unload ramoops since pstore doesn't support
> -        * unregistering yet.
> -        */
>         struct ramoops_context *cxt = &oops_cxt;
>
> -       iounmap(cxt->virt_addr);
> -       release_mem_region(cxt->phys_addr, cxt->size);
> -       cxt->max_dump_cnt = 0;
> +       pstore_unregister();
>
> -       /* TODO(kees): When pstore supports unregistering, call it here. */
> +       cxt->max_dump_cnt = 0;
>         kfree(cxt->pstore.buf);
>         cxt->pstore.bufsize = 0;
>
> +       persistent_ram_free(cxt->mprz);
> +       persistent_ram_free(cxt->fprz);
> +       persistent_ram_free(cxt->cprz);
> +       ramoops_free_przs(cxt);
> +
>         return 0;
> -#endif
> -       return -EBUSY;
>  }
>
>  static struct platform_driver ramoops_driver = {
>         .probe          = ramoops_probe,
> -       .remove         = __exit_p(ramoops_remove),
> +       .remove         = ramoops_remove,
>         .driver         = {
>                 .name   = "ramoops",
>         },
> diff --git a/include/linux/pstore.h b/include/linux/pstore.h
> index 8e7a25b..34e4a6d 100644
> --- a/include/linux/pstore.h
> +++ b/include/linux/pstore.h
> @@ -77,6 +77,7 @@ struct pstore_info {
>
>  #ifdef CONFIG_PSTORE
>  extern int pstore_register(struct pstore_info *);
> +extern void pstore_unregister(void);
>  extern bool pstore_cannot_block_path(enum kmsg_dump_reason reason);
>  #else
>  static inline int
> @@ -84,6 +85,10 @@ pstore_register(struct pstore_info *psi)
>  {
>         return -ENODEV;
>  }
> +static inline void
> +pstore_unregister(void)
> +{
> +}
>  static inline bool
>  pstore_cannot_block_path(enum kmsg_dump_reason reason)
>  {
> --
> 2.5.0
>
>

Cool! Thanks for working on the unregister logic!

-Kees

-- 
Kees Cook
Chrome OS Security
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