Messages in this thread Patch in this message | | | Date | Mon, 7 Dec 2015 23:14:30 +0100 | Subject | Re: [PATCH] ARM: mm: mark section-aligned portion of rodata NX | From | Ard Biesheuvel <> |
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On 7 December 2015 at 22:56, Kees Cook <keescook@chromium.org> wrote: > On Mon, Dec 7, 2015 at 1:52 PM, Ard Biesheuvel > <ard.biesheuvel@linaro.org> wrote: >> On 7 December 2015 at 21:54, Kees Cook <keescook@chromium.org> wrote: >>> 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. >>> >>> Signed-off-by: Kees Cook <keescook@chromium.org> >>> --- >>> I am baffled why I can't put the ALIGN in the ".start = " initializer. >>> GCC seems to think it's non-static, but only because of the "&" operator. >>> Does anyone see a way to do this that doesn't require the runtime ALIGN? >> >> Yes, but you need to move the ALIGN() expression to the linker script >> as the value of a new symbol > > I didn't see a way to do this without actually bumping the alignment > (CONFIG_DEBUG_ALIGN_RODATA already does that, I want the other case). > Do you have an example anywhere I could look at? >
Something like this (untested)
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S index 8b60fde5ce48..9fb98c5dd35b 100644 --- a/arch/arm/kernel/vmlinux.lds.S +++ b/arch/arm/kernel/vmlinux.lds.S @@ -336,6 +336,8 @@ SECTIONS STABS_DEBUG }
+__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 8a63b4cdc0f2..ddacd3bd8f8b 100644 --- a/arch/arm/mm/init.c +++ b/arch/arm/mm/init.c @@ -592,15 +592,13 @@ static struct section_perm nx_perms[] = { .mask = ~PMD_SECT_XN, .prot = PMD_SECT_XN, }, -#ifdef CONFIG_DEBUG_RODATA /* Make rodata NX (set RO in ro_perms below). */ { - .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 };
#ifdef CONFIG_DEBUG_RODATA
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