[PATCH v2 4/5] arm64: mmu: map .text as read-only from the outset
From: mark.rutland@arm.com (Mark Rutland)
Date: 2017-02-14 15:57:05
Also in:
kvmarm
On Sat, Feb 11, 2017 at 08:23:05PM +0000, Ard Biesheuvel wrote:
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. Reviewed-by: Laura Abbott <redacted> Reviewed-by: Kees Cook <redacted> Signed-off-by: Ard Biesheuvel <redacted>
This generally looks good. One effect of this is that even with rodata=off, external debuggers can't install SW breakpoints via the executable mapping. We might want to allow that to be overridden. e.g. make rodata= an early param, and switch the permissions based on that in map_kernel(), e.g. have: pgprot_t text_prot = rodata_enabled ? PAGE_KERNEL_ROX : PAGE_KERNEL_EXEC); ... and use that for .text and .init.text by default. Thanks, Mark.
quoted hunk ↗ jump to hunk
--- arch/arm64/mm/mmu.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-)diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 7ed981c7f4c0..e97f1ce967ec 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; - create_mapping_late(__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.@@ -484,7 +481,7 @@ 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); + map_kernel_segment(pgd, _text, _etext, PAGE_KERNEL_ROX, &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