[PATCH v3 4/5] arm64: mmu: map .text as read-only from the outset
From: Ard Biesheuvel <hidden>
Date: 2017-02-14 20:52:37
Also in:
kvmarm
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
Now that alternatives patching code no longer relies on the primary mapping of .text being writable, we can remove the code that removes the writable permissions post-init time, and map it read-only from the outset. To preserve the existing behavior under rodata=off, which is relied upon by external debuggers to manage software breakpoints (as pointed out by Mark), add an early_param() check for rodata=, and use RWX permissions if it set to 'off'. Reviewed-by: Laura Abbott <redacted> Reviewed-by: Kees Cook <redacted> Signed-off-by: Ard Biesheuvel <redacted> --- arch/arm64/mm/mmu.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index b7ce0b9ad096..70a492b36fe7 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c@@ -442,9 +442,6 @@ void mark_rodata_ro(void) { unsigned long section_size; - section_size = (unsigned long)_etext - (unsigned long)_text; - update_mapping_prot(__pa_symbol(_text), (unsigned long)_text, - section_size, PAGE_KERNEL_ROX); /* * mark .rodata as read only. Use __init_begin rather than __end_rodata * to cover NOTES and EXCEPTION_TABLE.
@@ -477,6 +474,12 @@ static void __init map_kernel_segment(pgd_t *pgd, void *va_start, void *va_end, vm_area_add_early(vma); } +static int __init parse_rodata(char *arg) +{ + return strtobool(arg, &rodata_enabled); +} +early_param("rodata", parse_rodata); + /* * Create fine-grained mappings for the kernel. */
@@ -484,7 +487,9 @@ static void __init map_kernel(pgd_t *pgd) { static struct vm_struct vmlinux_text, vmlinux_rodata, vmlinux_init, vmlinux_data; - map_kernel_segment(pgd, _text, _etext, PAGE_KERNEL_EXEC, &vmlinux_text); + pgprot_t text_prot = rodata_enabled ? PAGE_KERNEL_ROX : PAGE_KERNEL_EXEC; + + map_kernel_segment(pgd, _text, _etext, text_prot, &vmlinux_text); map_kernel_segment(pgd, __start_rodata, __init_begin, PAGE_KERNEL, &vmlinux_rodata); map_kernel_segment(pgd, __init_begin, __init_end, PAGE_KERNEL_EXEC, &vmlinux_init);
--
2.7.4