Re: [PATCH RFC 1/7] x86/head/64: Mark startup_gdt and startup_gdt_descr as __initdata

[H. Peter Anvin]

On October 17, 2023 6:02:27 AM PDT, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>
>* Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx> wrote:
>
>> Hi Ingo,
>> 
>> I have sent patch #6 separately for x86. Do you have any ideas about 
>> building the head code as PIE? Should I resend the patchset for the PIE 
>> feature?
>
>So I had a brief look, and despite reading 0/43 it was unclear to me what 
>the precise advantages of building as PIE are.
>
>Ie. could you please outline:
>
> - *Exactly* how much PIE based KASLR randomization would gain us in terms 
>   of randomization granularity and effective number of randomization bits, 
>   compared to the current status quo?
>
> - How is code generation changed at the instruction level - how does 
>   kernel size change and what are the micro-advantages/disadvantages?
>
> - Are there any other advantages/motivation than improving KASLR?
>
>Ie. before asking us to apply ~50 patches and add a whole new build mode 
>and the maintainance overhead to support it into infinity and beyond, could 
>you please offer a better list of pros and cons?
>
>Thanks,
>
>	Ingo

If the goal is better KASLR, then what we really should spend time on was Kristen Accardi's fgKASLR patches, which not only exponentially(!) increases the randomization entrophy but also *actually* avoids the "one leak and it's over" problem.

However, she gave up on it because she got no interest, despite working code.