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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 15:46:13 +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 14:46:29 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16/06/2026 2:50 pm, Jan Beulich wrote:
> 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?
Frediano pointed out that I read the script incorrectly.
.reloc needs to be non-discardable
.rodata needs to be writeable because of editing the relocations in it.
~Andrew
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