linux-kernel - Re: [RFC] Circumventing FineIBT Via Entrypoints

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Message-ID: <48212481-75ef-43e1-afa1-ec1d603a91a0@citrix.com>
Date: Sat, 15 Feb 2025 00:11:17 +0000
From: Andrew Cooper <andrew.cooper3@...rix.com>
To: Jennifer Miller <jmill@....edu>
Cc: Jann Horn <jannh@...gle.com>, Andy Lutomirski <luto@...nel.org>,
 linux-hardening@...r.kernel.org, kees@...nel.org, joao@...rdrivepizza.com,
 samitolvanen@...gle.com, kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] Circumventing FineIBT Via Entrypoints

On 15/02/2025 12:07 am, Jennifer Miller wrote:
> On Fri, Feb 14, 2025 at 11:06:50PM +0000, Andrew Cooper wrote:
>> On 13/02/2025 11:24 pm, Jennifer Miller wrote:
>>> On Thu, Feb 13, 2025 at 09:24:18PM +0000, Andrew Cooper wrote:
>>> Still, I hadn't considered misusing readonly/unmapped pages on the GPR
>>> register spill that follows. Could we enforce that the stack pointer we get
>>> be page aligned to prevent this vector? So that if one were to attempt to
>>> point the stack to readonly or unmapped memory they should be guaranteed to
>>> double fault?
>> Hmm.
>>
>> Espfix64 does involve #DF recovering from a write to a read-only stack. 
>> (This broken corner of x86 is also fixed in FRED.   We fixed a *lot* of
>> thing.)
> Interesting, I haven't gotten around to reading into how FRED works, it
> sounds neat.

Start with
https://docs.google.com/document/d/1hWejnyDkjRRAW-JEsRjA5c9CKLOPc6VKJQsuvODlQEI/edit?usp=sharing


Then
https://www.intel.com/content/www/us/en/content-details/779982/flexible-return-and-event-delivery-fred-specification.html

~Andrew