Re: [PATCH v3 4/4] x86: Split .init section to satisfy UEFI CA memory mitigation

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.06.2026 16:58, Andrew Cooper wrote:
> On 16/06/2026 12:20 pm, Marek Marczykowski-Górecki wrote:
>> On Tue, Jun 16, 2026 at 11:13:36AM +0100, Frediano Ziglio wrote:
>>> From: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
>>>
>>> Currently .init section is both writeable and executable, split data and 
>>> code
>>> to have 2 sections satisfying W^X rule.
>>>
>>> It is a requirement for NX_COMPAT so the PE can be loaded with W^X perms
>>> in the pagetables.
>>>
>>> NX_COMPAT is a requirement from shim-review,
>>> https://github.com/rhboot/shim-review#do-you-have-the-nx-bit-set-in-your-shim-if-so-is-your-entire-boot-stack-nx-compatible-and-what-testing-have-you-done-to-ensure-such-compatibility
>>>
>>> Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>
>> Acked-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
>>
>> Is that the last piece necessary to satisfy the NX_COMPAT requirement? If
>> so, I suppose a subsequent patch should actually set the
>> IMAGE_DLLCHARACTERISTICS_NX_COMPAT bit (IIUC ld --nxcompat option), right?
> 
> The manpage says:
> 
>        --nxcompat
>        --disable-nxcompat
>            The image is compatible with the Data Execution Prevention. 
> This feature was introduced with MS Windows XP SP2 for i386 PE targets. 
> The option is enabled by default.
> 
> It turns out that Xen is being marked NX_COMPAT even prior to this
> series, which is deeply suspicious as it has an RWX init section.

The defaults used by ld are (imo wrongly) driven by Cygwin's / MinGW's
desires. They apparently assert that all binaries should be NX-compatible,
with merely a way to opt out. There's no dependency on section attributes
afaict.

Jan