linux-kernel - Re: [PATCH] x86/kexec: Add a sanity check on previous kernel's ima kexec buffer

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Message-ID: <CAMj1kXFDAypcEAAFw=O6pS5zD5aujXUvo3_95p_2fJiESsSmgQ@mail.gmail.com>
Date: Tue, 2 Dec 2025 08:16:27 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Mimi Zohar <zohar@...ux.ibm.com>
Cc: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>, henry.willard@...cle.com, 
	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>, Andrew Morton <akpm@...ux-foundation.org>, 
	"Mike Rapoport (Microsoft)" <rppt@...nel.org>, Jiri Bohac <jbohac@...e.cz>, 
	Sourabh Jain <sourabhjain@...ux.ibm.com>, Guo Weikang <guoweikang.kernel@...il.com>, 
	Joel Granados <joel.granados@...nel.org>, Alexander Graf <graf@...zon.com>, 
	Sohil Mehta <sohil.mehta@...el.com>, Jonathan McDowell <noodles@...com>, linux-kernel@...r.kernel.org, 
	yifei.l.liu@...cle.com, stable@...r.kernel.org, 
	Paul Webb <paul.x.webb@...cle.com>
Subject: Re: [PATCH] x86/kexec: Add a sanity check on previous kernel's ima
 kexec buffer

On Mon, 1 Dec 2025 at 22:43, Mimi Zohar <zohar@...ux.ibm.com> wrote:
>
> On Mon, 2025-12-01 at 15:03 +0530, Harshit Mogalapalli wrote:
> > Hi all,
> >
> > On 13/11/25 01:00, Harshit Mogalapalli wrote:
> > > When the second-stage kernel is booted via kexec with a limiting command
> > > line such as "mem=<size>", the physical range that contains the carried
> > > over IMA measurement list may fall outside the truncated RAM leading to
> > > a kernel panic.
> > >
> > >      BUG: unable to handle page fault for address: ffff97793ff47000
> > >      RIP: ima_restore_measurement_list+0xdc/0x45a
> > >      #PF: error_code(0x0000) – not-present page
> > >
> > > Other architectures already validate the range with page_is_ram(), as
> > > done in commit: cbf9c4b9617b ("of: check previous kernel's
> > > ima-kexec-buffer against memory bounds") do a similar check on x86.
>
> It should be obvious that without carrying the measurement list across kexec,
> that attestation will fail.  Please mentioned it here in the patch description.
>

Couldn't we just use memremap() and be done with it? That will use the
direct map if the memory is mapped, or vmap() it otherwise.