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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id y14sm872468oih.23.2020.02.06.04.41.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Feb 2020 04:41:48 -0800 (PST) Date: Thu, 6 Feb 2020 04:41:46 -0800 From: Kees Cook To: Kristen Carlson Accardi Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, arjan@linux.intel.com, rick.p.edgecombe@intel.com, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, Jessica Yu Subject: Re: [RFC PATCH 10/11] module: Reorder functions Message-ID: <202002060440.E7ED91B@keescook> References: <20200205223950.1212394-1-kristen@linux.intel.com> <20200205223950.1212394-11-kristen@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200205223950.1212394-11-kristen@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 05, 2020 at 02:39:49PM -0800, Kristen Carlson Accardi wrote: > If a module has functions split out into separate text sections > (i.e. compiled with the -ffunction-sections flag), reorder the > functions to provide some code diversification to modules. > > Signed-off-by: Kristen Carlson Accardi Probably a good idea to add Jessica to CC in next version: Jessica Yu Reviewed-by: Kees Cook -Kees > --- > kernel/module.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 85 insertions(+) > > diff --git a/kernel/module.c b/kernel/module.c > index b56f3224b161..231563e95e61 100644 > --- a/kernel/module.c > +++ b/kernel/module.c > @@ -53,6 +53,8 @@ > #include > #include > #include > +#include > +#include > #include > #include "module-internal.h" > > @@ -3245,6 +3247,87 @@ static int find_module_sections(struct module *mod, struct load_info *info) > return 0; > } > > +/* > + * shuffle_text_list() > + * Use a Fisher Yates algorithm to shuffle a list of text sections. > + */ > +static void shuffle_text_list(Elf_Shdr **list, int size) > +{ > + int i; > + unsigned int j; > + Elf_Shdr *temp; > + > + for (i = size - 1; i > 0; i--) { > + /* > + * TBD - seed. We need to be able to use a known > + * seed so that we can non-randomly randomize for > + * debugging. > + */ > + > + // pick a random index from 0 to i > + get_random_bytes(&j, sizeof(j)); > + j = j % (i + 1); > + > + temp = list[i]; > + list[i] = list[j]; > + list[j] = temp; > + } > +} > + > +/* > + * randomize_text() > + * Look through the core section looking for executable code sections. > + * Store sections in an array and then shuffle the sections > + * to reorder the functions. > + */ > +static void randomize_text(struct module *mod, struct load_info *info) > +{ > + int i; > + int num_text_sections = 0; > + Elf_Shdr **text_list; > + int size = 0; > + int max_sections = info->hdr->e_shnum; > + unsigned int sec = find_sec(info, ".text"); > + > + if (!IS_ENABLED(CONFIG_FG_KASLR) || !kaslr_enabled()) > + return; > + > + if (sec == 0) > + return; > + > + text_list = kmalloc_array(max_sections, sizeof(*text_list), GFP_KERNEL); > + if (text_list == NULL) > + return; > + > + for (i = 0; i < max_sections; i++) { > + Elf_Shdr *shdr = &info->sechdrs[i]; > + const char *sname = info->secstrings + shdr->sh_name; > + > + if (!(shdr->sh_flags & SHF_ALLOC) || > + !(shdr->sh_flags & SHF_EXECINSTR) || > + strstarts(sname, ".init")) > + continue; > + > + text_list[num_text_sections] = shdr; > + num_text_sections++; > + } > + > + shuffle_text_list(text_list, num_text_sections); > + > + for (i = 0; i < num_text_sections; i++) { > + Elf_Shdr *shdr = text_list[i]; > + unsigned int infosec; > + const char *sname; > + > + sname = info->secstrings + shdr->sh_name; > + infosec = shdr->sh_info; > + > + shdr->sh_entsize = get_offset(mod, &size, shdr, infosec); > + } > + > + kfree(text_list); > +} > + > static int move_module(struct module *mod, struct load_info *info) > { > int i; > @@ -3282,6 +3365,8 @@ static int move_module(struct module *mod, struct load_info *info) > } else > mod->init_layout.base = NULL; > > + randomize_text(mod, info); > + > /* Transfer each section which specifies SHF_ALLOC */ > pr_debug("final section addresses:\n"); > for (i = 0; i < info->hdr->e_shnum; i++) { > -- > 2.24.1 > -- Kees Cook