Messages in this thread Patch in this message |  | | From | Kees Cook <> | Subject | [PATCH 2/2] ARM: mm: keep rodata non-executable | Date | Thu, 13 Feb 2014 17:04:10 -0800 |
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Introduce "CONFIG_DEBUG_RODATA" to mostly match the x86 config, though the behavior is different: it depends on STRICT_KERNMEM_PERMS, which sets rodata read-only (but executable), where as this option additionally splits rodata from the kernel text (resulting in potentially more memory lost to padding) and sets it non-executable as well. The end result is that on builds with CONFIG_DEBUG_RODATA=y (like x86) the rodata with be marked purely read-only.
Signed-off-by: Kees Cook <keescook@chromium.org> --- arch/arm/include/asm/cacheflush.h | 5 +++++ arch/arm/kernel/vmlinux.lds.S | 3 +++ arch/arm/mm/Kconfig | 12 ++++++++++++ arch/arm/mm/init.c | 8 ++++++++ 4 files changed, 28 insertions(+)
diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h index e9a49fe0284e..2b058fc7a188 100644 --- a/arch/arm/include/asm/cacheflush.h +++ b/arch/arm/include/asm/cacheflush.h @@ -486,4 +486,9 @@ int set_memory_rw(unsigned long addr, int numpages); int set_memory_x(unsigned long addr, int numpages); int set_memory_nx(unsigned long addr, int numpages); +#ifdef CONFIG_DEBUG_RODATA +/* This has already happened during free_initmem. */ +static inline void mark_rodata_ro(void) { } +#endif + #endif diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S index 08fa667ef2f1..ec79e7268e09 100644 --- a/arch/arm/kernel/vmlinux.lds.S +++ b/arch/arm/kernel/vmlinux.lds.S @@ -120,6 +120,9 @@ SECTIONS ARM_CPU_KEEP(PROC_INFO) } +#ifdef CONFIG_DEBUG_RODATA + . = ALIGN(1<<SECTION_SHIFT); +#endif RO_DATA(PAGE_SIZE) . = ALIGN(4); diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig index 999eb505faee..7c8bbe7e2769 100644 --- a/arch/arm/mm/Kconfig +++ b/arch/arm/mm/Kconfig @@ -968,3 +968,15 @@ config ARM_KERNMEM_PERMS region is padded to section-size (1MiB) boundaries (because their permissions are different and splitting the 1M pages into 4K ones causes TLB performance problems), wasting memory. + +config DEBUG_RODATA + bool "Split rodata from text and set it read-only/non-executable" + depends on ARM_KERNMEM_PERMS + default y + help + If this is set, rodata will be split from kernel text and made + non-executable. (This option already depends on the option + CONFIG_STRICT_KERNMEM_PERMS which makes rodata read-only, though + still executable.) This creates another section-size padded + region, so it can waste more memory space while gaining a pure + read-only rodata region. diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c index f0b1df53f436..5b1b049501b9 100644 --- a/arch/arm/mm/init.c +++ b/arch/arm/mm/init.c @@ -656,6 +656,14 @@ struct section_perm __initdata section_perms[] = { .prot = PMD_SECT_APX | PMD_SECT_AP_WRITE, #endif }, +#ifdef CONFIG_DEBUG_RODATA + /* Make rodata RO (set NX). */ + { + .start = (unsigned long)__start_rodata, + .end = (unsigned long)__init_begin, + .prot = PMD_SECT_XN, + } +#endif }; static inline void section_update(unsigned long addr, pmdval_t prot) -- 1.7.9.5
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