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Re: [PATCH v3 4/4] x86: Split .init section to satisfy UEFI CA memory mitigation
- To: Jan Beulich <jbeulich@xxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Frediano Ziglio <freddy77@xxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 16 Jun 2026 13:40:52 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Frediano Ziglio <frediano.ziglio@xxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>
- Delivery-date: Tue, 16 Jun 2026 12:41:06 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16/06/2026 1:30 pm, Jan Beulich wrote:
> On 16.06.2026 13:29, 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?
>> We need to satisfy everything in
>> https://github.com/xenserver/xen.pg/blob/XS-9/patches/correct-sections-permissions.patch
>>
>> .reloc needs to be non-discardable and writeable.
> Writable? Why?
Because we take fatal pagefaults against it when it's really read-only.
But as for why, I'll have to defer that to Frediano/Ross who did the
work originally.
>
>> This will require a very recent binutils and a patch (series?) from Jan.
> Seeing that no patch had been submitted so far, I recently added this to my
> todo list, yes. But really I was hoping that someone else would make the
> small change that I expect is going to be needed.
If you can explain what change is needed then maybe someone else can do it.
But right now, all I know is it's a new binutils and "something".
~Andrew
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