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Re: [PATCH] Arm: avoid .init.data to be marked as executable

  • To: Julien Grall <julien@xxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Mon, 14 Jun 2021 12:02:43 +0200
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  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Mon, 14 Jun 2021 10:03:01 +0000
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On 14.06.2021 11:41, Julien Grall wrote:
> On 11/06/2021 11:39, Jan Beulich wrote:
>> This confuses disassemblers, at the very least. Move
>> .altinstr_replacement to .init.text,
> The alternative code was borrowed from Linux. The code has now changed 
> to cater very large kernel. They used to keep the .altinstr_replacement 
> and altinstructions close to each other (albeit they were both in 
> .init.text).
> I am not entirely why, but I am a bit worry to separate them. What sort 
> of test did you do?

Well, just build tests, on the assumption that relocation overflows
would be reported by the linker if the sections ended up too far

>> dropping the redundant ALIGN().
>> Also, to have .altinstr_replacement have consistent attributes in the
>> object files, add "x" to the one instance where it was missing. >
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> I'm uncertain whether having .altinstr_replacement inside or outside the
>> [_sinittext,_einittext) region is better; I simply followed what we have
>> on the x86 side right now.
> This means the altinstructions will be marked executable in the 
> page-table. They technically should not be executable, so I would move 
> them outside _einittext and make sure the section is aligned to a PAGE_SIZE.

Hmm, are you saying you bother getting attributes right for .init.*
in the page tables? I ask because we don't on x86, and because it
would seem wasteful to me to pad to PAGE_SIZE just for this. But
you're the maintainer, i.e. I'm merely double checking ...




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