linux-kernel - Re: [PATCH v7 8/8] [DO NOT MERGE] x86/kexec: Add CFI type information to relocate

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Message-ID: <9e31213361f1d13aff1e0a26ffc29955e462f72d.camel@infradead.org>
Date: Sat, 22 Mar 2025 11:38:24 +0000
From: David Woodhouse <dwmw2@...radead.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: kexec@...ts.infradead.org, Thomas Gleixner <tglx@...utronix.de>, Ingo
 Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
 <dave.hansen@...ux.intel.com>, x86@...nel.org, "H . Peter Anvin"
 <hpa@...or.com>,  "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
 Kai Huang <kai.huang@...el.com>, Nikolay Borisov <nik.borisov@...e.com>, 
 linux-kernel@...r.kernel.org, Simon Horman <horms@...nel.org>, Dave Young
 <dyoung@...hat.com>, Peter Zijlstra <peterz@...radead.org>, bsz@...zon.de
Subject: Re: [PATCH v7 8/8] [DO NOT MERGE] x86/kexec: Add CFI type
 information to relocate_kernel()

On Wed, 2025-03-19 at 08:47 -0700, Josh Poimboeuf wrote:
> 
> Looking at machine_kexec(), it calls cet_disable() before the indirect
> call.  So yeah, it seems fine for relocate_kernel() to not have a CFI
> prologue or ENDBR.

Yeah. I'm just going to throw that into a branch and forget it for now.
It's just causing noise around the *actual* stuff we want to get in, to
do the exception handling.

For that, I think the only thing outstanding is to add a userspace test
based on http://david.woodhou.se/loadret.c which invokes the int3 from
the 'payload' to test it. I think this is better than doing it inside
the kernel itself, as it gives us a selftest for the kexec jump
mechanism too.

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