[PATCH v11 8/9] ima: make the kexec extra memory configurable

[Mimi Zohar]

On Thu, 2025-04-10 at 09:59 -0700, steven chen wrote:
> On 4/10/2025 2:54 AM, Baoquan He wrote:
> > On 04/02/25 at 05:47am, steven chen wrote:
> > > The extra memory allocated for carrying the IMA measurement list across
> > > kexec is hard-coded as half a PAGE.  Make it configurable.
> > > 
> > > Define a Kconfig option, IMA_KEXEC_EXTRA_MEMORY_KB, to configure the
> > > extra memory (in kb) to be allocated for IMA measurements added during
> > > kexec soft reboot.  Ensure the default value of the option is set such
> > > that extra half a page of memory for additional measurements is allocated
> > > for the additional measurements.
> > > 
> > > Update ima_add_kexec_buffer() function to allocate memory based on the
> > > Kconfig option value, rather than the currently hard-coded one.
> > > 
> > > Suggested-by: Stefan Berger <stefanb at linux.ibm.com>
> > > Signed-off-by: Tushar Sugandhi <tusharsu at linux.microsoft.com>
> > > Signed-off-by: steven chen <chenste at linux.microsoft.com>
> > > Reviewed-by: Stefan Berger <stefanb at linux.ibm.com>
> > > Reviewed-by: Mimi Zohar <zohar at linux.ibm.com>
> > > ---
> > >   security/integrity/ima/Kconfig     | 10 ++++++++++
> > >   security/integrity/ima/ima_kexec.c | 16 +++++++++++-----
> > >   2 files changed, 21 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> > > index 475c32615006..d73c96c3c1c9 100644
> > > --- a/security/integrity/ima/Kconfig
> > > +++ b/security/integrity/ima/Kconfig
> > > @@ -321,4 +321,14 @@ config IMA_DISABLE_HTABLE
> > >   	help
> > >   	   This option disables htable to allow measurement of duplicate records.
> > >   
> > > +config IMA_KEXEC_EXTRA_MEMORY_KB
> > > +	int "Extra memory for IMA measurements added during kexec soft reboot"
> > > +	depends on IMA_KEXEC
> > > +	default 0
> > Usually a new Kconfig item which accepts a range should define the range
> > boundary, otherwise it's not clear to people how large or how small it
> > can be set. For example, can I set it as value of 1<<40? We should at
> > least estimate a possible upper limit for it for other people's
> > reference. My personal opinion.
> 
> Hi Baoquan,
> 
> How about I set range 2-40? Default set as 2, same as the fixed setting.

0, the current default, sets the "extra" memory to the existing "extra half a
page of memory for the additional measurements".  For backwards compatibility,
please do not change this.

The requirement for a larger "extra" measurement is coming from Microsoft. If
this isn't any longer a requirement, we could drop this patch.  Lakshmi, do you
have any thoughts on this?

thanks,

Mimi

> 
> > The rest looks good to me.
> > 
> > 
> > > +	help
> > > +	  IMA_KEXEC_EXTRA_MEMORY_KB determines the extra memory to be
> > > +	  allocated (in kb) for IMA measurements added during kexec soft reboot.
> > > +	  If set to the default value of 0, an extra half page of memory for those
> > > +	  additional measurements will be allocated.
> > > +
> > >   endif
> > ...snip...
> 
> 
>