| Message ID | 1488637848-13588-5-git-send-email-ard.biesheuvel@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sat, Mar 04, 2017 at 02:30:46PM +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. > > 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 <labbott@redhat.com> > Reviewed-by: Kees Cook <keescook@chromium.org> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > 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 df377fbe464e..edd982f88714 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -416,9 +416,6 @@ 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. > @@ -451,6 +448,12 @@ 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. > */ > @@ -458,7 +461,9 @@ 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; > + It might be worth having a comment as to why, e.g. /* * External debuggers may need to write directly to the text * mapping to install SW breakpoints. Allow this (only) when * explicitly requested with rodata=off. */ ... otherwise this looks fine. FWIW, either way: Reviewed-by: Mark Rutland <mark.rutland@arm.com> Thanks, Mark. > + 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 >
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index df377fbe464e..edd982f88714 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -416,9 +416,6 @@ 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. @@ -451,6 +448,12 @@ 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. */ @@ -458,7 +461,9 @@ 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);