Re: [PATCH v2 08/11] firmware: enable run time change of forcing fallback loader

[Kees Cook]

On Fri, Feb 23, 2018 at 6:46 PM, Luis R. Rodriguez <mcgrof@xxxxxxxxxx> wrote:
> Currently one requires to test four kernel configurations to test the
> firmware API completely:
>
> 0)
>   CONFIG_FW_LOADER=y
>
> 1)
>   o CONFIG_FW_LOADER=y
>   o CONFIG_FW_LOADER_USER_HELPER=y
>
> 2)
>   o CONFIG_FW_LOADER=y
>   o CONFIG_FW_LOADER_USER_HELPER=y
>   o CONFIG_FW_LOADER_USER_HELPER_FALLBACK=y
>
> 3) When CONFIG_FW_LOADER=m the built-in stuff is disabled, we have
>    no current tests for this.
>
> We can reduce the requirements to three kernel configurations by making
> fw_config.force_sysfs_fallback a proc knob we flip on off. For kernels that
> disable CONFIG_IKCONFIG_PROC this can also enable one to inspect if
> CONFIG_FW_LOADER_USER_HELPER_FALLBACK was enabled at build time by checking
> the proc value at boot time.

You'll still need compile tests of each configuration, but I love that
this will give one kernel to test them all.

Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees


>
> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
> ---
>  drivers/base/firmware_fallback.c       |  1 +
>  drivers/base/firmware_fallback.h       |  4 +++-
>  drivers/base/firmware_fallback_table.c | 17 +++++++++++++++++
>  kernel/sysctl.c                        | 11 +++++++++++
>  4 files changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/firmware_fallback.c b/drivers/base/firmware_fallback.c
> index 47690207e0ee..cbce9a950cd8 100644
> --- a/drivers/base/firmware_fallback.c
> +++ b/drivers/base/firmware_fallback.c
> @@ -7,6 +7,7 @@
>  #include <linux/security.h>
>  #include <linux/highmem.h>
>  #include <linux/umh.h>
> +#include <linux/sysctl.h>
>
>  #include "firmware_fallback.h"
>  #include "firmware_loader.h"
> diff --git a/drivers/base/firmware_fallback.h b/drivers/base/firmware_fallback.h
> index 550498c7fa4c..ca7e69a8417b 100644
> --- a/drivers/base/firmware_fallback.h
> +++ b/drivers/base/firmware_fallback.h
> @@ -12,12 +12,14 @@
>   *
>   * @force_sysfs_fallback: force the sysfs fallback mechanism to be used
>   *     as if one had enabled CONFIG_FW_LOADER_USER_HELPER_FALLBACK=y.
> + *     Useful to help debug a CONFIG_FW_LOADER_USER_HELPER_FALLBACK=y
> + *     functionality on a kernel where that config entry has been disabled.
>   * @old_timeout: for internal use
>   * @loading_timeout: the timeout to wait for the fallback mechanism before
>   *     giving up, in seconds.
>   */
>  struct firmware_fallback_config {
> -       const bool force_sysfs_fallback;
> +       unsigned int force_sysfs_fallback;
>         int old_timeout;
>         int loading_timeout;
>  };
> diff --git a/drivers/base/firmware_fallback_table.c b/drivers/base/firmware_fallback_table.c
> index 53cc4e492520..77300d5e9c52 100644
> --- a/drivers/base/firmware_fallback_table.c
> +++ b/drivers/base/firmware_fallback_table.c
> @@ -19,6 +19,9 @@
>  /* Module or buit-in */
>  #ifdef CONFIG_FW_LOADER_USER_HELPER
>
> +static unsigned int zero;
> +static unsigned int one = 1;
> +
>  struct firmware_fallback_config fw_fallback_config = {
>         .force_sysfs_fallback = IS_ENABLED(CONFIG_FW_LOADER_USER_HELPER_FALLBACK),
>         .loading_timeout = 60,
> @@ -26,4 +29,18 @@ struct firmware_fallback_config fw_fallback_config = {
>  };
>  EXPORT_SYMBOL_GPL(fw_fallback_config);
>
> +struct ctl_table firmware_config_table[] = {
> +       {
> +               .procname       = "force_sysfs_fallback",
> +               .data           = &fw_fallback_config.force_sysfs_fallback,
> +               .maxlen         = sizeof(unsigned int),
> +               .mode           = 0644,
> +               .proc_handler   = proc_douintvec_minmax,
> +               .extra1         = &zero,
> +               .extra2         = &one,
> +       },
> +       { }
> +};
> +EXPORT_SYMBOL_GPL(firmware_config_table);
> +
>  #endif
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index acdf4e85c0a1..aa8355953fcf 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -253,6 +253,10 @@ extern struct ctl_table random_table[];
>  extern struct ctl_table epoll_table[];
>  #endif
>
> +#ifdef CONFIG_FW_LOADER_USER_HELPER
> +extern struct ctl_table firmware_config_table[];
> +#endif
> +
>  #ifdef HAVE_ARCH_PICK_MMAP_LAYOUT
>  int sysctl_legacy_va_layout;
>  #endif
> @@ -748,6 +752,13 @@ static struct ctl_table kern_table[] = {
>                 .mode           = 0555,
>                 .child          = usermodehelper_table,
>         },
> +#ifdef CONFIG_FW_LOADER_USER_HELPER
> +       {
> +               .procname       = "firmware_config",
> +               .mode           = 0555,
> +               .child          = firmware_config_table,
> +       },
> +#endif
>         {
>                 .procname       = "overflowuid",
>                 .data           = &overflowuid,
> --
> 2.16.2
>



-- 
Kees Cook
Pixel Security