diff mbox

arm64: Align .text section to PAGE_SIZE

Message ID CAKv+Gu_QKpL2X3ZNn9QVZnBa00JrF1v0W1DtkyuGzm1cLREPWg@mail.gmail.com
State New
Headers show

Commit Message

Ard Biesheuvel Oct. 23, 2015, 4:49 p.m. UTC 
(+ Laura)

http://thread.gmane.org/gmane.linux.ports.arm.kernel/450513

On 23 October 2015 at 18:32, Jeremy Linton <jeremy.linton@arm.com> wrote:
> On 10/23/2015 10:34 AM, Ard Biesheuvel wrote:

>>

>> 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.


Yes.

> 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.

>


This should do the trick then, I think:
------8<----------
------8<----------

>         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.

-- 
Ard.

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Comments

Ard Biesheuvel Oct. 24, 2015, 2:29 a.m. UTC | #1 
(+ Laura, correct email this time)

http://thread.gmane.org/gmane.linux.ports.arm.kernel/450513

On 23 October 2015 at 20:13, Jeremy Linton <jeremy.linton@arm.com> wrote:
> On 10/23/2015 11:49 AM, Ard Biesheuvel wrote:

>>

>> On 23 October 2015 at 18:32, Jeremy Linton <jeremy.linton@arm.com> wrote:

>

> ...

>>>

>>>          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.

>

> ...

>

> 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...

>


OK, I didn't catch that. Not sure if the average waste of 32 KB is
worth the trouble, though. Especially since, in my opinion,
CONFIG_DEBUG_RODATA should be promoted to a non-debug 'default y'
option.

-- 
Ard.

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

>

> Thanks,

>

>


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diff mbox

Patch

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index e9b8276ca079..db834a464986 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -104,7 +104,7 @@  SECTIONS
                _text = .;
                HEAD_TEXT
        }
-       ALIGN_DEBUG_RO
+       ALIGN_DEBUG_RO_MIN(PAGE_SIZE)
        .text : {                       /* Real text segment            */
                _stext = .;             /* Text and read-only data      */
                        __exception_text_start = .;