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Re: [PATCH v3 4/4] x86: Split .init section to satisfy UEFI CA memory mitigation
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Frediano Ziglio <freddy77@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 16 Jun 2026 15:50:25 +0200
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- Cc: 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 13:50:29 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16.06.2026 14:40, Andrew Cooper wrote:
> 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.
Wasn't this for relocations _against_ r/o sections, not the .reloc section
itself?
Jan
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