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Date:   Thu, 16 Jun 2022 10:59:27 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Mimi Zohar <zohar@linux.ibm.com>
Cc:     Jonathan McDowell <noodles@fb.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-integrity@vger.kernel.org" <linux-integrity@vger.kernel.org>,
        "linux-security-module@vger.kernel.org" 
        <linux-security-module@vger.kernel.org>,
        "kexec@lists.infradead.org" <kexec@lists.infradead.org>
Subject: Re: [PATCH v5] x86/kexec: Carry forward IMA measurement log on kexec
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On 06/13/22 at 05:01pm, Mimi Zohar wrote:
> On Mon, 2022-06-13 at 10:30 +0000, Jonathan McDowell wrote:
> > On kexec file load Integrity Measurement Architecture (IMA) subsystem
> > may verify the IMA signature of the kernel and initramfs, and measure
> > it. The command line parameters passed to the kernel in the kexec call
> > may also be measured by IMA. A remote attestation service can verify
> > a TPM quote based on the TPM event log, the IMA measurement list, and
> > the TPM PCR data. This can be achieved only if the IMA measurement log
> > is carried over from the current kernel to the next kernel across
> > the kexec call.
> > 
> > powerpc and ARM64 both achieve this using device tree with a
> > "linux,ima-kexec-buffer" node. x86 platforms generally don't make use of
> > device tree, so use the setup_data mechanism to pass the IMA buffer to
> > the new kernel.
> > 
> > (Mimi, Baoquan, I haven't included your reviewed-bys because this has
> >  changed the compile guards around the ima_(free|get)_kexec_buffer
> >  functions in order to fix the warning the kernel test robot found. I
> >  think this is the right thing to do and avoids us compiling them on
> >  platforms where they won't be used. The alternative would be to drop
> >  the guards in ima.h that Mimi requested for v4.)hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
> > 
> > Signed-off-by: Jonathan McDowell <noodles@fb.com>
> > ---
> > v5:
> >  - Guard ima_(free|get)_kexec_buffer functions with
> >    CONFIG_HAVE_IMA_KEXEC (kernel test robot)
> >  - Use setup_data_offset in setup_boot_parameters and update rather than
> >    calculating in call to setup_ima_state.
> > v4:
> >  - Guard ima.h function prototypes with CONFIG_HAVE_IMA_KEXEC
> 
> > diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
> > index 8d374cc552be..42a6c5721a43 100644
> > --- a/drivers/of/kexec.c
> > +++ b/drivers/of/kexec.c
> > @@ -9,6 +9,7 @@
> >   *  Copyright (C) 2016  IBM Corporation
> >   */
> >  
> > +#include <linux/ima.h>
> >  #include <linux/kernel.h>
> >  #include <linux/kexec.h>
> >  #include <linux/memblock.h>
> > @@ -115,6 +116,7 @@ static int do_get_kexec_buffer(const void *prop, int len, unsigned long *addr,
> >  	return 0;
> >  }
> >  
> > +#ifdef CONFIG_HAVE_IMA_KEXEC
> >  /**
> >   * ima_get_kexec_buffer - get IMA buffer from the previous kernel
> >   * @addr:	On successful return, set to point to the buffer contents.
> > @@ -173,6 +175,7 @@ int ima_free_kexec_buffer(void)
> >  
> >  	return memblock_phys_free(addr, size);
> >  }
> > +#endif
> 
> Inside ima_{get,free}_kexec_buffer(), there's no need now to test
> whether CONFIG_HAVE_IMA_KEXEC is enabled.
> 
>         if (!IS_ENABLED(CONFIG_HAVE_IMA_KEXEC))
>                 return -ENOTSUPP;

Indeed. The #ifdef added by Jonathan is redundant. Not sure if the
original IS_ENABLED(CONFIG_HAVE_IMA_KEXEC) checking inside
ima_{get,free}_kexec_buffer() is intended. I ever reviewed below patch,
the IS_ENABLED(CONFIG_XX) inside static function will make the function
compiled, and will be optimized out if the CONFIG_XX is not enabled.
However, it only has effect on static function. Here,
ima_{get,free}_kexec_buffer() is not static, likely we should remove the
inside IS_ENABLED() checking.

commit 4ece09be9913a87ff99ea347fd7e7adad5bdbc8f
Author: Jisheng Zhang <jszhang@kernel.org>
Date:   Wed Mar 23 16:06:39 2022 -0700

    x86/setup: use IS_ENABLED(CONFIG_KEXEC_CORE) instead of #ifdef
    
    Replace the conditional compilation using "#ifdef CONFIG_KEXEC_CORE" by a
    check for "IS_ENABLED(CONFIG_KEXEC_CORE)", to simplify the code and
    increase compile coverage.

Other than this one Mimi pointed out, this patch looks good to me, thx.

Reviewed-by: Baoquan He <bhe@redhat.com>

> 
> 
> >  
> >  /**
> >   * remove_ima_buffer - remove the IMA buffer property and reservation from @fdt
> > diff --git a/include/linux/ima.h b/include/linux/ima.h
> 
>