From 64ac2e74f0b21505606faf725cb5633d63b8b728 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Tue, 26 Jan 2016 01:20:21 +0100 Subject: [PATCH] ARM: 8502/1: mm: mark section-aligned portion of rodata NX When rodata is large enough that it crosses a section boundary after the kernel text, mark the rest NX. This is as close to full NX of rodata as we can get without splitting page tables or doing section alignment via CONFIG_DEBUG_ALIGN_RODATA. When the config is: CONFIG_DEBUG_RODATA=y # CONFIG_DEBUG_ALIGN_RODATA is not set Before: ---[ Kernel Mapping ]--- 0x80000000-0x80100000 1M RW NX SHD 0x80100000-0x80a00000 9M ro x SHD 0x80a00000-0xa0000000 502M RW NX SHD After: ---[ Kernel Mapping ]--- 0x80000000-0x80100000 1M RW NX SHD 0x80100000-0x80700000 6M ro x SHD 0x80700000-0x80a00000 3M ro NX SHD 0x80a00000-0xa0000000 502M RW NX SHD Signed-off-by: Kees Cook Reviewed-by: Ard Biesheuvel Signed-off-by: Russell King --- arch/arm/kernel/vmlinux.lds.S | 9 +++++++-- arch/arm/mm/init.c | 7 ++++--- 2 files changed, 11 insertions(+), 5 deletions(-) diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S index e087a2ed112b..fdca231e150a 100644 --- a/arch/arm/kernel/vmlinux.lds.S +++ b/arch/arm/kernel/vmlinux.lds.S @@ -12,9 +12,7 @@ #include #include #include -#ifdef CONFIG_DEBUG_RODATA #include -#endif #define PROC_INFO \ . = ALIGN(4); \ @@ -319,6 +317,13 @@ SECTIONS STABS_DEBUG } +/* + * Without CONFIG_DEBUG_ALIGN_RODATA, __start_rodata_section_aligned will + * be the first section-aligned location after __start_rodata. Otherwise, + * it will be equal to __start_rodata. + */ +__start_rodata_section_aligned = ALIGN(__start_rodata, 1 << SECTION_SHIFT); + /* * These must never be empty * If you have to comment these two assert statements out, your diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c index 53f42508025b..370581aeb871 100644 --- a/arch/arm/mm/init.c +++ b/arch/arm/mm/init.c @@ -582,6 +582,9 @@ struct section_perm { pmdval_t clear; }; +/* First section-aligned location at or after __start_rodata. */ +extern char __start_rodata_section_aligned[]; + static struct section_perm nx_perms[] = { /* Make pages tables, etc before _stext RW (set NX). */ { @@ -599,16 +602,14 @@ static struct section_perm nx_perms[] = { .mask = ~PMD_SECT_XN, .prot = PMD_SECT_XN, }, -#ifdef CONFIG_DEBUG_ALIGN_RODATA /* Make rodata NX (set RO in ro_perms below). */ { .name = "rodata NX", - .start = (unsigned long)__start_rodata, + .start = (unsigned long)__start_rodata_section_aligned, .end = (unsigned long)__init_begin, .mask = ~PMD_SECT_XN, .prot = PMD_SECT_XN, }, -#endif }; static struct section_perm ro_perms[] = {