Re: [PATCH v4 3/3] x86: Align output sections for UEFI CA memory mitigation requirements

[Jan Beulich <jbeulich@suse.com>]

On 23.09.2024 18:06, Frediano Ziglio wrote:
> On Mon, Sep 23, 2024 at 4:54 PM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 19.09.2024 10:00, Frediano Ziglio wrote:
>>> All loadable sections should be page aligned.
>>
>> What about .buildid? .reloc otoh is discardable, and hence presumably okay
>> if mis-aligned.
> 
> Currently, internally we have a patch to make ".reloc" not discardaeble.
> The problem is that in case of direct EFI loading, that section is
> used to relocated back to the final location. On bootloaders
> discarding that section, you'll get a crash :-(

Indeed, if such EFI loaders exist we have an issue (I don't think we
actively mark the section discardable, I think that's something the
linker decides).

> Isn't ".buildid" a kind of subsection with the same attributes of
> container section?

In ELF maybe. In the PE binary it's following directly after .rodata,
meaning it typically shares its space with .rodata's last page. (Aiui
in PE/COFF it is illegal for multiple sections to overlap, unlike for
ELF's "segments", i.e. what the program header entries describe.)

> Maybe I have BUILD_ID_EFI not defined?

Possible, albeit would be odd.

Jan