[PATCH v2] arm64: Align .text section to PAGE_SIZE

[Mark Rutland]

On Mon, Oct 26, 2015 at 02:09:58PM -0700, Laura Abbott wrote:
> On 10/26/15 1:26 PM, Mark Rutland wrote:
> >>Perhaps it would be better to have something like the following (with
> >>PAGE_SHIFT sorted out to be includable in a linker script), so any
> >>ALIGN_DEBUG_RO* correctly aligns things to whatever boundary is
> >>required, and we don't need to over-align things in the !DEBUG_RO_DATA
> >>case.
> >
> >Ignore the bit about PAGE_SHIFT and linker script. I'd got confused as I
> >had a local typo breaking the build.
> >
> >With the below diff applied I can boot a defconfig +CONFIG_DEBUG_RODATA
> >+CONFIG_ARM64_64K_PAGES v4.3-rc7 kernel on Juno
> >
> 
> Most of the alignment was found by trial and error so I suspect it was
> just getting lucky before. I think this should be covering all the
> cases. Hopefully the protections will make it more restrictive instead
> of less to catch any more corner cases.

Hopefully!

On a somewhat related note, we should probably move .rodata away from
.text; currently we give everything between _stext and _etext
PAGE_KERNEL_EXEC permissions (i.e. !PXN), and .rodata has no reason to
be executable.

Doing so would also make it simpler to add .rodata to the mem_init
notice, which I've been meaning to do for a while.

I can take a look at shuffling sections for that tomorrow.

> For whoever ends up submitting the patch,
> 
> Reviewed-by: Laura Abbott <laura at labbott.name>

Cheers; I'll spin this as a full patch momentarily.

Thanks,
Mark.

> >>---->8----
> >>diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> >>index 9807333..4d77757 100644
> >>--- a/arch/arm64/kernel/vmlinux.lds.S
> >>+++ b/arch/arm64/kernel/vmlinux.lds.S
> >>@@ -60,9 +60,12 @@ PECOFF_FILE_ALIGNMENT = 0x200;
> >>  #define PECOFF_EDATA_PADDING
> >>  #endif
> >>
> >>-#ifdef CONFIG_DEBUG_ALIGN_RODATA
> >>+#if defined(CONFIG_DEBUG_ALIGN_RODATA)
> >>  #define ALIGN_DEBUG_RO                 . = ALIGN(1<<SECTION_SHIFT);
> >>  #define ALIGN_DEBUG_RO_MIN(min)                ALIGN_DEBUG_RO
> >>+#elif defined(CONFIG_DEBUG_RODATA)
> >>+#define ALIGN_DEBUG_RO                 . = ALIGN(1<<PAGE_SHIFT);
> >>+#define ALIGN_DEBUG_RO_MIN(min)                ALIGN_DEBUG_RO
> >>  #else
> >>  #define ALIGN_DEBUG_RO
> >>  #define ALIGN_DEBUG_RO_MIN(min)                . = ALIGN(min);
>