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Re: [PATCH v3 1/4] Align relevant sections to 4KB
- To: Frediano Ziglio <freddy77@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 16 Jun 2026 17:07:56 +0200
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- Cc: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 16 Jun 2026 15:08:03 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16.06.2026 16:38, Frediano Ziglio wrote:
> On Tue, 16 Jun 2026 at 13:27, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>
>> On 16.06.2026 12:13, Frediano Ziglio wrote:
>>> From: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
>>>
>>> Required by UEFI CA memory mitigation.
>>>
>>> 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
>>>
>>> Sections with different permissions must be in separate pages.
>>> In the case of debug sections they are contiguous and have the same
>>> permissions so it's not an issue if they are not aligned to the page.
>>
>> What if .debug_* starts in the middle of a page? Aren't you further
>> relying on .debug_* to be r/o (i.e. neither X nor W)? (Right now
>> .reloc is what comes immediately ahead of .debug_*, and that's r/o
>> as well, so not an issue in practice for now. Yet as indicated, the
>> description here wants to be usable as a reference when this later
>> needs extending / revisiting.)
>
> Can you suggest a better wording?
After "have the same permissions" insert ", including the immediately
preceding .reloc section,"?
> Practically I think before the .debug section you could have the
> .reloc or the SBAT, either are permission-compatible.
Right, just that this doesn't go without saying.
> If in the future we break it for some reason we'll fix it again.
Yet better would be if we didn't break it.
Jan
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