Date:   Tue, 14 Feb 2023 15:21:19 +0000
From:   Thomas =?utf-8?Q?Wei=C3=9Fschuh?= <linux@weissschuh.net>
To:     Coly Li <colyli@suse.de>
Cc:     Kent Overstreet <kent.overstreet@gmail.com>,
        linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] bcache: make kobj_type structures constant
Message-ID: <20230214152119.epkfhkojqjvokqmv@t-8ch.de>
References: <20230214-kobj_type-bcache-v1-1-cf00ead7bee7@weissschuh.net>
 <125CA8D6-D3B7-42FB-83BE-DCA688F2ACAF@suse.de>
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On Tue, Feb 14, 2023 at 05:51:09PM +0800, Coly Li wrote:
> 
> 
> > 2023年2月14日 11:13，Thomas Weißschuh <linux@weissschuh.net> 写道：
> > 
> > Since commit ee6d3dd4ed48 ("driver core: make kobj_type constant.")
> > the driver core allows the usage of const struct kobj_type.
> > 
> > Take advantage of this to constify the structure definitions to prevent
> > modification at runtime.
> > 
> 
> How the const structure definition can prevent modification at run time?

It will be put into .rodata instead of .data by the compiler.
The .rodata section is mapped as read-only via the pagetable.

See Documentation/security/self-protection.rst
"Function pointers and sensitive variables must not be writable".

Thomas

> Thanks.
> 
> Coly Li
> 
> 
> > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> > ---
> > drivers/md/bcache/bcache.h | 10 +++++-----
> > drivers/md/bcache/sysfs.h  |  2 +-
> > 2 files changed, 6 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> > index aebb7ef10e63..a522f4f1f992 100644
> > --- a/drivers/md/bcache/bcache.h
> > +++ b/drivers/md/bcache/bcache.h
> > @@ -1004,11 +1004,11 @@ extern struct workqueue_struct *bch_flush_wq;
> > extern struct mutex bch_register_lock;
> > extern struct list_head bch_cache_sets;
> > 
> > -extern struct kobj_type bch_cached_dev_ktype;
> > -extern struct kobj_type bch_flash_dev_ktype;
> > -extern struct kobj_type bch_cache_set_ktype;
> > -extern struct kobj_type bch_cache_set_internal_ktype;
> > -extern struct kobj_type bch_cache_ktype;
> > +extern const struct kobj_type bch_cached_dev_ktype;
> > +extern const struct kobj_type bch_flash_dev_ktype;
> > +extern const struct kobj_type bch_cache_set_ktype;
> > +extern const struct kobj_type bch_cache_set_internal_ktype;
> > +extern const struct kobj_type bch_cache_ktype;
> > 
> > void bch_cached_dev_release(struct kobject *kobj);
> > void bch_flash_dev_release(struct kobject *kobj);
> > diff --git a/drivers/md/bcache/sysfs.h b/drivers/md/bcache/sysfs.h
> > index a2ff6447b699..65b8bd975ab1 100644
> > --- a/drivers/md/bcache/sysfs.h
> > +++ b/drivers/md/bcache/sysfs.h
> > @@ -3,7 +3,7 @@
> > #define _BCACHE_SYSFS_H_
> > 
> > #define KTYPE(type) \
> > -struct kobj_type type ## _ktype = { \
> > +const struct kobj_type type ## _ktype = { \
> > .release = type ## _release, \
> > .sysfs_ops = &((const struct sysfs_ops) { \
> > .show = type ## _show, \
> > 
> > ---
> > base-commit: f6feea56f66d34259c4222fa02e8171c4f2673d1
> > change-id: 20230214-kobj_type-bcache-6d2bd129b0fa
> > 
> > Best regards,
> > -- 
> > Thomas Weißschuh <linux@weissschuh.net>
> > 
>