[PATCH v9 12/15] module: Reorder functions
From: Alexander Lobakin <hidden>
Date: 2021-12-23 00:26:38
Also in:
linux-hardening, linux-kbuild, live-patching, lkml, llvm
Subsystem:
kernel build + files below scripts/ (unless maintained elsewhere), the rest · Maintainers:
Nathan Chancellor, Nicolas Schier, Linus Torvalds
From: Kristen Carlson Accardi <redacted> Introduce a new config option to allow modules to be re-ordered by function. This option can be enabled independently of the kernel text KASLR or FG_KASLR settings so that it can be used by architectures that do not support either of these features. This option will be selected by default if CONFIG_FG_KASLR is selected. 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. alobakin: Make it work with ClangCFI -- in such builds, .text section must always come first and be page-aligned. Exclude it from the shuffle list and leave as it is. Make this feature depend on `-z unique-symbol` as well, due to the very same reasons. Traditionally, use common shuffle_array() from <linux/random.h>. Signed-off-by: Kristen Carlson Accardi <redacted> Reviewed-by: Kees Cook <redacted> Acked-by: Ard Biesheuvel <ardb@kernel.org> Tested-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Tony Luck <tony.luck@intel.com> Tested-by: Tony Luck <tony.luck@intel.com> Acked-by: Jessica Yu <jeyu@kernel.org> Tested-by: Jessica Yu <jeyu@kernel.org> Reported-by: kernel test robot <redacted> # swap.cocci Co-developed-by: Alexander Lobakin <redacted> Signed-off-by: Alexander Lobakin <redacted> --- Makefile | 6 +++- include/linux/linkage.h | 1 + init/Kconfig | 14 ++++++++ kernel/module.c | 73 +++++++++++++++++++++++++++++++++++++++-- 4 files changed, 91 insertions(+), 3 deletions(-)
diff --git a/Makefile b/Makefile
index 3346269341d4..74d270c77d96 100644
--- a/Makefile
+++ b/Makefile@@ -900,7 +900,7 @@ export SECSUBST_AFLAGS endif # Same for modules. LD DCE doesn't work for them, thus not checking for it -ifneq ($(CONFIG_LTO_CLANG),) +ifneq ($(CONFIG_MODULE_FG_KASLR)$(CONFIG_LTO_CLANG),) KBUILD_AFLAGS_MODULE += -Wa,--sectname-subst KBUILD_CFLAGS_MODULE += -Wa,--sectname-subst endif
@@ -909,6 +909,10 @@ endif # CONFIG_HAVE_ASM_FUNCTION_SECTIONS # ClangLTO implies `-ffunction-sections -fdata-sections`, no need # to specify them manually and trigger a pointless full rebuild ifndef CONFIG_LTO_CLANG +ifdef CONFIG_MODULE_FG_KASLR +KBUILD_CFLAGS_MODULE += -ffunction-sections +endif + ifneq ($(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION)$(CONFIG_FG_KASLR),) KBUILD_CFLAGS_KERNEL += -ffunction-sections endif
diff --git a/include/linux/linkage.h b/include/linux/linkage.h
index f3c96fb6a534..deb26069278a 100644
--- a/include/linux/linkage.h
+++ b/include/linux/linkage.h@@ -80,6 +80,7 @@ #if defined(CONFIG_HAVE_ASM_FUNCTION_SECTIONS) && \ ((defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) && !defined(MODULE)) || \ (defined(CONFIG_FG_KASLR) && !defined(MODULE)) || \ + (defined(CONFIG_MODULE_FG_KASLR) && defined(MODULE)) || \ (defined(CONFIG_LTO_CLANG))) #define SYM_PUSH_SECTION(name) \
diff --git a/init/Kconfig b/init/Kconfig
index 381b063b4925..38c82e21efd7 100644
--- a/init/Kconfig
+++ b/init/Kconfig@@ -2376,6 +2376,20 @@ config UNUSED_KSYMS_WHITELIST one per line. The path can be absolute, or relative to the kernel source tree. +config MODULE_FG_KASLR + bool "Module Function Granular Layout Randomization" + depends on $(cc-option,-ffunction-sections) + depends on LD_HAS_Z_UNIQUE_SYMBOL || !LIVEPATCH + default FG_KASLR + depends on BROKEN + help + This option randomizes the module text section by reordering the text + section by function at module load time. In order to use this + feature, the module must have been compiled with the + -ffunction-sections compiler flag. + + If unsure, say N. + endif # MODULES config MODULES_TREE_LOOKUP
diff --git a/kernel/module.c b/kernel/module.c
index 84a9141a5e15..802e1098eaf4 100644
--- a/kernel/module.c
+++ b/kernel/module.c@@ -57,6 +57,7 @@ #include <linux/bsearch.h> #include <linux/dynamic_debug.h> #include <linux/audit.h> +#include <linux/random.h> #include <uapi/linux/module.h> #include "module-internal.h"
@@ -1527,7 +1528,7 @@ static void free_sect_attrs(struct module_sect_attrs *sect_attrs) for (section = 0; section < sect_attrs->nsections; section++) kfree(sect_attrs->attrs[section].battr.attr.name); - kfree(sect_attrs); + kvfree(sect_attrs); } static void add_sect_attrs(struct module *mod, const struct load_info *info)
@@ -1544,7 +1545,7 @@ static void add_sect_attrs(struct module *mod, const struct load_info *info) size[0] = ALIGN(struct_size(sect_attrs, attrs, nloaded), sizeof(sect_attrs->grp.bin_attrs[0])); size[1] = (nloaded + 1) * sizeof(sect_attrs->grp.bin_attrs[0]); - sect_attrs = kzalloc(size[0] + size[1], GFP_KERNEL); + sect_attrs = kvzalloc(size[0] + size[1], GFP_KERNEL); if (sect_attrs == NULL) return;
@@ -2416,6 +2417,71 @@ static bool module_init_layout_section(const char *sname) return module_init_section(sname); } +/* + * 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 max_sections = info->hdr->e_shnum; + int num_text_sections = 0; + Elf_Shdr **text_list; + int i, size; + + text_list = kvmalloc_array(max_sections, sizeof(*text_list), GFP_KERNEL); + if (!text_list) + 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) || + (shdr->sh_flags & ARCH_SHF_SMALL) || + module_init_layout_section(sname)) + continue; + + /* + * With CONFIG_CFI_CLANG, .text with __cfi_check() must come + * before any other text sections, and be aligned to PAGE_SIZE. + * Don't include it in the shuffle list. + */ + if (IS_ENABLED(CONFIG_CFI_CLANG) && !strcmp(sname, ".text")) + continue; + + if (!num_text_sections) + size = shdr->sh_entsize; + + text_list[num_text_sections] = shdr; + num_text_sections++; + } + + if (!num_text_sections) + goto exit; + + shuffle_array(text_list, num_text_sections); + + for (i = 0; i < num_text_sections; i++) { + Elf_Shdr *shdr = text_list[i]; + + /* + * get_offset has a section index for it's last + * argument, that is only used by arch_mod_section_prepend(), + * which is only defined by parisc. Since this type + * of randomization isn't supported on parisc, we can + * safely pass in zero as the last argument, as it is + * ignored. + */ + shdr->sh_entsize = get_offset(mod, &size, shdr, 0); + } + +exit: + kvfree(text_list); +} + /* * Lay out the SHF_ALLOC sections in a way not dissimilar to how ld * might -- code, read-only data, read-write data, small data. Tally
@@ -2510,6 +2576,9 @@ static void layout_sections(struct module *mod, struct load_info *info) break; } } + + if (IS_ENABLED(CONFIG_MODULE_FG_KASLR)) + randomize_text(mod, info); } static void set_license(struct module *mod, const char *license)
--
2.33.1