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[209.85.222.45]) by smtp.gmail.com with ESMTPSA id 2sm14376864vke.27.2019.04.10.09.26.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Apr 2019 09:26:57 -0700 (PDT) Received: by mail-ua1-f45.google.com with SMTP id c6so992011uan.1 for ; Wed, 10 Apr 2019 09:26:56 -0700 (PDT) X-Received: by 2002:ab0:4eaa:: with SMTP id l42mr18185593uah.80.1554913615771; Wed, 10 Apr 2019 09:26:55 -0700 (PDT) MIME-Version: 1.0 References: <20190410011418.76408-1-joel@joelfernandes.org> In-Reply-To: <20190410011418.76408-1-joel@joelfernandes.org> From: Kees Cook Date: Wed, 10 Apr 2019 09:26:44 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/2] module: Prepare for addition of new ro_after_init sections To: "Joel Fernandes (Google)" Cc: LKML , "Paul E. McKenney" , Steven Rostedt , Mathieu Desnoyers , rcu@vger.kernel.org, Kernel Hardening , Android Kernel Team , Kees Cook , Jessica Yu Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 9, 2019 at 6:14 PM Joel Fernandes (Google) wrote: > > For the purposes of hardening modules by adding sections to > ro_after_init sections, prepare for addition of new ro_after_init > entries which we do in future patches. Create a table to which new > entries could be added later. This makes it less error prone and reduce > code duplication. > > Cc: paulmck@linux.vnet.ibm.com > Cc: rostedt@goodmis.org > Cc: mathieu.desnoyers@efficios.com > Cc: rcu@vger.kernel.org > Cc: kernel-hardening@lists.openwall.com > Cc: kernel-team@android.com > Suggested-by: keescook@chromium.org > Signed-off-by: Joel Fernandes (Google) > > --- > kernel/module.c | 42 ++++++++++++++++++++++++------------------ > 1 file changed, 24 insertions(+), 18 deletions(-) > > diff --git a/kernel/module.c b/kernel/module.c > index 524da609c884..f9221381d076 100644 > --- a/kernel/module.c > +++ b/kernel/module.c > @@ -3300,11 +3300,28 @@ static bool blacklisted(const char *module_name) > } > core_param(module_blacklist, module_blacklist, charp, 0400); > > +/* > + * Mark ro_after_init section with SHF_RO_AFTER_INIT so that > + * layout_sections() can put it in the right place. > + * Note: ro_after_init sections also have SHF_{WRITE,ALLOC} set. > + */ > +static char *ro_after_init_sections[] = { static const char * const ... Need to make sure the table and its strings can't be changed. :) > + ".data..ro_after_init", > + > + /* > + * __jump_table structures are never modified, with the exception of > + * entries that refer to code in the __init section, which are > + * annotated as such at module load time. > + */ > + "__jump_table", > + NULL Since this table is known at build time, you don't need a NULL terminator, you can use ARRAY_SIZE() instead. > +}; > + > static struct module *layout_and_allocate(struct load_info *info, int flags) > { > struct module *mod; > unsigned int ndx; > - int err; > + int err, i; > > err = check_modinfo(info->mod, info, flags); > if (err) > @@ -3319,23 +3336,12 @@ static struct module *layout_and_allocate(struct load_info *info, int flags) > /* We will do a special allocation for per-cpu sections later. */ > info->sechdrs[info->index.pcpu].sh_flags &= ~(unsigned long)SHF_ALLOC; > > - /* > - * Mark ro_after_init section with SHF_RO_AFTER_INIT so that > - * layout_sections() can put it in the right place. > - * Note: ro_after_init sections also have SHF_{WRITE,ALLOC} set. > - */ > - ndx = find_sec(info, ".data..ro_after_init"); > - if (ndx) > - info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT; > - /* > - * Mark the __jump_table section as ro_after_init as well: these data > - * structures are never modified, with the exception of entries that > - * refer to code in the __init section, which are annotated as such > - * at module load time. > - */ > - ndx = find_sec(info, "__jump_table"); > - if (ndx) > - info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT; > + /* Set sh_flags for read-only after init sections */ > + for (i = 0; ro_after_init_sections[i]; i++) { i.e. for (i = 0; i < ARRAY_SIZE(ro_after_init_sections); i++) > + ndx = find_sec(info, ro_after_init_sections[i]); > + if (ndx) > + info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT; > + } > > /* Determine total sizes, and put offsets in sh_entsize. For now > this is done generically; there doesn't appear to be any Otherwise, yeah, looks good to me. -- Kees Cook