arm64: Align .text section to PAGE_SIZE

It appears that 64k page kernel's die early, in a somewhat random set

of locations when built without KVM. Most likely during memblock manipulations (depending on kernel debug options).

Normally when KVM is built into the kernel it has an explicit PAGE_SIZE alignment requirement and that forces the text section to be aligned to PAGE_SIZE. Without it, the alignment granularity is likely to be 4k.

This updates the linker script to assure that the the text section is aligned to a minimum of PAGE_SIZE regardless of build options.

Signed-off-by Jeremy Linton <[email protected]>

---
 arch/arm64/kernel/vmlinux.lds.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

arch/arm64/kernel/vmlinux.lds.S +1 -2

index 8a5d97b..bf7b972 100644
@@ -92,7 +92,7 @@ SECTIONS
                HEAD_TEXT
        }
        ALIGN_DEBUG_RO
-       .text : {                       /* Real text segment            */
+       .text ALIGN(PAGE_SIZE) : {      /* Real text segment            */
                _stext = .;             /* Text and read-only data      */
                        __exception_text_start = .;
                        *(.exception.text)
--

2.4.3

It looks like fixup_executable() [with DEBUG_RODATA enabled] is the culprit here: it calls create mapping() with a size that gets rounded up to a multiple of PAGE_SIZE, which means the region that ends up getting its exec bits cleared is larger than it should. Perhaps it is better to fix that instead?

Quoted 6 lines · Ard Biesheuvel

It looks like fixup_executable() [with DEBUG_RODATA enabled] is the culprit here: it calls create mapping() with a size that gets rounded up to a multiple of PAGE_SIZE, which means the region that ends up getting its exec bits cleared is larger than it should. Perhaps it is better to fix that instead?

Ard,
Thanks for taking a look at this!

Your probably right.

But AFAIK, with just that fix text/ro sections can be partially
mapped without ro.

It seems to me that putting a little padding in so that
they are on separate pages is a good idea, especially since it seems the remaining sections of interest are page aligned, either explicitly in the linker script or via assembly directives in assorted places.

Maybe a clearer fix is an additional ifdef in the DEBUG_ALIGN_RODATA
stanza which sets ALIGN_DEBUG_RO to align to pagesize if DEBUG_RODATA is set, that way it only takes affect for RODATA.

On 23 October 2015 at 18:32, Jeremy Linton <[email protected]> wrote:

Quoted 3 lines

Maybe a clearer fix is an additional ifdef in the DEBUG_ALIGN_RODATA
stanza which sets ALIGN_DEBUG_RO to align to pagesize if DEBUG_RODATA is set, that way it only takes affect for RODATA.

I think the diff does what you mean here.

Quoted 2 lines · Ard Biesheuvel

On 23 October 2015 at 18:32, Jeremy Linton <[email protected]> wrote:

...

Quoted 7 lines

Quoted 5 lines

Maybe a clearer fix is an additional ifdef in the
DEBUG_ALIGN_RODATA
stanza which sets ALIGN_DEBUG_RO to align to pagesize if DEBUG_RODATA is set, that way it only takes affect for RODATA.

Quoted 1 line

I think the diff does what you mean here.

...

This solves the problem I have. But, my comment about was trying to be a little more creative and allow it to align at less than page size if DEBUG_RODATA isn't set, as it does today. Sort of a packed kernel if you will...

But I will re-post shortly with just the ALIGN_DEBUG_RO change you suggest.

Thanks,