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

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Message-ID: <93bd3c308c79414b3c620216b20d5962fcaccd15.camel@linux.ibm.com>
Date: Tue, 02 Dec 2025 14:10:47 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Ard Biesheuvel <ardb@...nel.org>
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>,
        Roberto Sassu	
 <roberto.sassu@...weicloud.com>,
        linux-integrity@...r.kernel.org
Subject: Re: [PATCH] x86/kexec: Add a sanity check on previous kernel's ima
 kexec buffer

[Cc: Roberto Sassu, linux-integrity]

On Tue, 2025-12-02 at 08:16 +0100, Ard Biesheuvel wrote:
> 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 mention 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.

No, the IMA measurement list is not a continuous buffer, but a linked list of
records with varying types of fields and field sizes.  The call to
ima_dump_measurement_list() marshals the measurement list into a buffer, while
ima_restore_measurement_list() unmarshals it.

-- 
thanks,

Mimi