On Fri, Jul 22, 2022 at 11:24 AM Mauricio Faria de Oliveira
<mfo@xxxxxxxxxxxxx> wrote:
>
> In order to expose a sysctl entry to modpost (file2alias.c, precisely)
> we have to shadow 'struct ctl_table' in mod_devicetable.h, as scripts
> should not access kernel headers or its types (see file2alias.c).
>
> The required field is '.procname' (basename of '/proc/sys/.../entry').
>
> Since 'struct ctl_table' is annotated for structure randomization and
> we need a known offset for '.procname' (remember, no kernel headers),
> take it out of the randomized portion (as in, eg, 'struct task_struct').
>
> Of course, add build-time checks for struct size and .procname offset
> between both structs. (This has to be done on kernel side; for headers.)
>
> With that in place, use the regular macros in devicetable-offsets.c to
> define SIZE_... and OFF_... macros for the shadow struct and the field
> of interest.
>
> Signed-off-by: Mauricio Faria de Oliveira <mfo@xxxxxxxxxxxxx>
> ---
> fs/proc/proc_sysctl.c | 19 +++++++++++++++++++
> include/linux/mod_devicetable.h | 25 +++++++++++++++++++++++++
> include/linux/sysctl.h | 11 ++++++++++-
> kernel/sysctl.c | 1 +
> scripts/mod/devicetable-offsets.c | 3 +++
> 5 files changed, 58 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 021e83fe831f..ebbf8702387e 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -19,6 +19,24 @@
> #include <linux/kmemleak.h>
> #include "internal.h"
>
> +#ifdef CONFIG_MODULES
> +#include <linux/mod_devicetable.h>
> +
> +static void check_struct_sysctl_device_id(void)
> +{
> + /*
> + * The shadow struct sysctl_device_id for file2alias.c needs
> + * the same size of struct ctl_table and offset for procname.
> + */
> + BUILD_BUG_ON(sizeof(struct sysctl_device_id)
> + != sizeof(struct ctl_table));
> + BUILD_BUG_ON(offsetof(struct sysctl_device_id, procname)
> + != offsetof(struct ctl_table, procname));
Nit:
If you use static_assert(), you can remove
check_struct_sysctl_device_id().
You can write static_assert() out of a function.
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 223376959d29..15073621cfa8 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2487,6 +2487,7 @@ int __init sysctl_init_bases(void)
>
> return 0;
> }
> +
Noise.
> #endif /* CONFIG_SYSCTL */
> /*
> * No sense putting this after each symbol definition, twice,
> diff --git a/scripts/mod/devicetable-offsets.c b/scripts/mod/devicetable-offsets.c
> index c0d3bcb99138..43b2549940d2 100644
> --- a/scripts/mod/devicetable-offsets.c
> +++ b/scripts/mod/devicetable-offsets.c
> @@ -262,5 +262,8 @@ int main(void)
> DEVID(ishtp_device_id);
> DEVID_FIELD(ishtp_device_id, guid);
>
> + DEVID(sysctl_device_id);
> + DEVID_FIELD(sysctl_device_id, procname);
> +
> return 0;
> }
> --
> 2.25.1
>
--
Best Regards
Masahiro Yamada
