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

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Message-ID: <20251201181909.GCaS3cHcsBjmYblRHG@fat_crate.local>
Date: Mon, 1 Dec 2025 19:19:09 +0100
From: Borislav Petkov <bp@...en8.de>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
Cc: henry.willard@...cle.com, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	"Mike Rapoport (Microsoft)" <rppt@...nel.org>,
	Jiri Bohac <jbohac@...e.cz>,
	Sourabh Jain <sourabhjain@...ux.ibm.com>,
	Guo Weikang <guoweikang.kernel@...il.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Joel Granados <joel.granados@...nel.org>,
	Alexander Graf <graf@...zon.com>,
	Sohil Mehta <sohil.mehta@...el.com>,
	Mimi Zohar <zohar@...ux.ibm.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, Dec 01, 2025 at 09:20:20AM -0800, Andrew Morton wrote:
> On Wed, 12 Nov 2025 11:30:02 -0800 Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com> 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.

Then why isn't there a ima_validate_range() function there which everyone
calls instead of the same check being replicated everywhere?

> > Cc: stable@...r.kernel.org
> > Fixes: b69a2afd5afc ("x86/kexec: Carry forward IMA measurement log on kexec")
> 
> That was via the x86 tree so I assume the x86 team (Boris?) will be
> processing this patch.

Yeah, it is on my to-deal-with-after-the-merge-window pile.

But since you've forced my hand... :-P

> I'll put it into mm.git's mm-hotfixes branch for now, to get a bit of
> testing and to generally track its progress.
> 
> > --- a/arch/x86/kernel/setup.c
> > +++ b/arch/x86/kernel/setup.c
> > @@ -439,9 +439,23 @@ int __init ima_free_kexec_buffer(void)
> >  
> >  int __init ima_get_kexec_buffer(void **addr, size_t *size)
> >  {
> > +	unsigned long start_pfn, end_pfn;
> > +
> >  	if (!ima_kexec_buffer_size)
> >  		return -ENOENT;
> >  
> > +	/*
> > +	 * Calculate the PFNs for the buffer and ensure
> > +	 * they are with in addressable memory.
> 
> "within" ;)
> 
> > +	 */
> > +	start_pfn = PFN_DOWN(ima_kexec_buffer_phys);
> > +	end_pfn = PFN_DOWN(ima_kexec_buffer_phys + ima_kexec_buffer_size - 1);
> > +	if (!pfn_range_is_mapped(start_pfn, end_pfn)) {
> > +		pr_warn("IMA buffer at 0x%llx, size = 0x%zx beyond memory\n",

This error message needs to be made a lot more user-friendly.

And pls do a generic helper as suggested above which ima code calls.

And by looking at the diff, there are two ima_get_kexec_buffer() functions in
the tree which could use some unification too ontop.

Right?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette