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 <[email protected]>
---
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));
+}
+#else
+static void check_struct_sysctl_device_id(void) {}
+#endif
+
#define list_for_each_table_entry(entry, table) \
for ((entry) = (table); (entry)->procname; (entry)++)
@@ -1779,6 +1797,7 @@ int __init proc_sys_init(void)
proc_sys_root->proc_dir_ops = &proc_sys_dir_file_operations;
proc_sys_root->nlink = 0;
+ check_struct_sysctl_device_id();
return sysctl_init_bases();
}
diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 549590e9c644..9cee024d8f2f 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -20,6 +20,31 @@ enum {
PCI_ID_F_VFIO_DRIVER_OVERRIDE = 1,
};
+/*
+ * "Device" table entry for a sysctl file (shadow of struct ctl_table).
+ *
+ * Only the procname field is reliable (known offset); all other fields
+ * are in the randomized portion of struct ctl_table, do NOT use them.
+ */
+struct sysctl_device_id {
+
+ /* This must be the first field (shadowed from struct ctl_table). */
+ const char *procname;
+
+ /* Here begins the randomizable portion of struct ctl_table. */
+
+ void *data;
+ int maxlen;
+ unsigned short mode; // umode_t in <linux/types.h>
+ void *child;
+ void *proc_handler;
+ void *poll;
+ void *extra1;
+ void *extra2;
+
+ /* Here ends the randomizable portion of struct ctl_table. */
+};
+
/**
* struct pci_device_id - PCI device ID structure
* @vendor: Vendor ID to match (or PCI_ANY_ID)
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 780690dc08cd..676112fde5ff 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -133,7 +133,13 @@ static inline void *proc_sys_poll_event(struct ctl_table_poll *poll)
/* A sysctl table is an array of struct ctl_table: */
struct ctl_table {
+
+ /* This must be the first field (shadowed to struct sysctl_device_id) */
const char *procname; /* Text ID for /proc/sys, or zero */
+
+ /* This begins the randomizable portion of the struct. */
+ randomized_struct_fields_start
+
void *data;
int maxlen;
umode_t mode;
@@ -142,7 +148,10 @@ struct ctl_table {
struct ctl_table_poll *poll;
void *extra1;
void *extra2;
-} __randomize_layout;
+
+ /* New fields go above here, so they are in the randomized portion. */
+ randomized_struct_fields_end
+};
struct ctl_node {
struct rb_node node;
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;
}
+
#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
On Fri, Jul 22, 2022 at 11:24 AM Mauricio Faria de Oliveira
<[email protected]> 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 <[email protected]>
> ---
> 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
On Tue, Jul 26, 2022 at 6:27 AM Masahiro Yamada <[email protected]> wrote:
>
> On Fri, Jul 22, 2022 at 11:24 AM Mauricio Faria de Oliveira
> <[email protected]> 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 <[email protected]>
> > ---
> > 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.
That's a nice cleanup; thanks!
>
>
>
> > 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.
Fixed.
>
>
>
>
> > #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
--
Mauricio Faria de Oliveira