linux-kernel - Re: [PATCH v2] Carry forward IMA measurement log on kexec on x86

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Date:   Tue, 3 May 2022 12:02:06 +0000
From:   Jonathan McDowell <noodles@...com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
CC:     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" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v2] Carry forward IMA measurement log on kexec on x86_64

On Fri, Apr 29, 2022 at 05:30:10PM -0400, Mimi Zohar wrote:
> > diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> > index 13753136f03f..419c50cfe6b9 100644
> > --- a/security/integrity/ima/ima_kexec.c
> > +++ b/security/integrity/ima/ima_kexec.c
> > @@ -10,6 +10,7 @@
> >  #include <linux/seq_file.h>
> >  #include <linux/vmalloc.h>
> >  #include <linux/kexec.h>
> > +#include <linux/memblock.h>
> >  #include <linux/of.h>
> >  #include <linux/ima.h>
> >  #include "ima.h"
> > @@ -134,10 +135,66 @@ void ima_add_kexec_buffer(struct kimage *image)
> >  }
> >  #endif /* IMA_KEXEC */
> >  
> > +#ifndef CONFIG_OF
> > +static phys_addr_t ima_early_kexec_buffer_phys;
> > +static size_t ima_early_kexec_buffer_size;
> > +
> > +void __init ima_set_kexec_buffer(phys_addr_t phys_addr, size_t size)
> > +{
> > +	if (size == 0)
> > +		return;
> > +
> > +	ima_early_kexec_buffer_phys = phys_addr;
> > +	ima_early_kexec_buffer_size = size;
> > +}
> > +
> > +int __init ima_free_kexec_buffer(void)
> > +{
> > +	int rc;
> > +
> > +	if (!IS_ENABLED(CONFIG_HAVE_IMA_KEXEC))
> > +		return -ENOTSUPP;
> > +
> > +	if (ima_early_kexec_buffer_size == 0)
> > +		return -ENOENT;
> > +
> > +	rc = memblock_phys_free(ima_early_kexec_buffer_phys,
> > +				ima_early_kexec_buffer_size);
> > +	if (rc)
> > +		return rc;
> > +
> > +	ima_early_kexec_buffer_phys = 0;
> > +	ima_early_kexec_buffer_size = 0;
> > +
> > +	return 0;
> > +}
> > +
> > +int __init ima_get_kexec_buffer(void **addr, size_t *size)
> > +{
> > +	if (!IS_ENABLED(CONFIG_HAVE_IMA_KEXEC))
> > +		return -ENOTSUPP;
> > +
> > +	if (ima_early_kexec_buffer_size == 0)
> > +		return -ENOENT;
> > +
> > +	*addr = __va(ima_early_kexec_buffer_phys);
> > +	*size = ima_early_kexec_buffer_size;
> > +
> > +	return 0;
> > +}
> > +
> 
> Originally both ima_get_kexec_buffer() and ima_free_kexec_buffer() were
> architecture specific.  Refer to commit 467d27824920 ("powerpc: ima:
> get the kexec buffer passed by the previous kernel").  Is there any
> need for defining them here behind an "#ifndef CONFIG_OF"?

Commit fee3ff99bc67 (powerpc: Move arch independent ima kexec functions
to drivers/of/kexec.c) moved those functions to drivers/of/kexec.c as a
more generic implementation so that ARM64 could use them too.

I think for platforms that use device tree that's the way to go, but the
functions to generically set + get the IMA buffer for non device tree
systems were useful enough to put in the IMA code rather than being x86
specific. If you disagree I can move them under arch/x86/ (assuming the
x86 folk agree using setup_data is the right way to go, I haven't seen
any of them comment on this approach yet).

> > +#else
> > +
> > +void __init ima_set_kexec_buffer(phys_addr_t phys_addr, size_t size)
> > +{
> > +	pr_warn("CONFIG_OF enabled, ignoring call to set buffer details.\n");
> > +}
> > +#endif /* CONFIG_OF */
> > +
> 
> Only when "HAVE_IMA_KEXEC" is defined is this file included.  Why is
> this warning needed?

x86 *can* have device tree enabled, but the only platform I'm aware that
did it was OLPC and I haven't seen any of the distros enable it. I put
this in so there's a warning if we have CONFIG_OF enabled on x86 and
tried to pass the IMA log via setup_data. Can remove (or fold into the
x86 code if we go that way).

> >  /*
> >   * Restore the measurement list from the previous kernel.
> >   */
> > -void ima_load_kexec_buffer(void)
> > +void __init ima_load_kexec_buffer(void)
> >  {
> >  	void *kexec_buffer = NULL;
> >  	size_t kexec_buffer_size = 0;

J.