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 <keescook@chromium.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 53f4250..370581a 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -582,6 +582,9 @@
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 @@
.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[] = {