Re: [PATCH v12 01/11] MODSIGN: Export module signature definitions

[Philipp Rudo]

Hi Thiago,

On Thu, 04 Jul 2019 15:57:34 -0300
Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx> wrote:

> Hello Philipp,
> 
> Philipp Rudo <prudo@xxxxxxxxxxxxx> writes:
> 
> > Hi Thiago,
> >
> >
> > On Thu, 04 Jul 2019 03:42:57 -0300
> > Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx> wrote:
> >  
> >> Jessica Yu <jeyu@xxxxxxxxxx> writes:
> >>   
> >> > +++ Thiago Jung Bauermann [27/06/19 23:19 -0300]:    
> >> >>IMA will use the module_signature format for append signatures, so export
> >> >>the relevant definitions and factor out the code which verifies that the
> >> >>appended signature trailer is valid.
> >> >>
> >> >>Also, create a CONFIG_MODULE_SIG_FORMAT option so that IMA can select it
> >> >>and be able to use mod_check_sig() without having to depend on either
> >> >>CONFIG_MODULE_SIG or CONFIG_MODULES.
> >> >>
> >> >>Signed-off-by: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx>
> >> >>Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> >> >>Cc: Jessica Yu <jeyu@xxxxxxxxxx>
> >> >>---
> >> >> include/linux/module.h           |  3 --
> >> >> include/linux/module_signature.h | 44 +++++++++++++++++++++++++
> >> >> init/Kconfig                     |  6 +++-
> >> >> kernel/Makefile                  |  1 +
> >> >> kernel/module.c                  |  1 +
> >> >> kernel/module_signature.c        | 46 ++++++++++++++++++++++++++
> >> >> kernel/module_signing.c          | 56 +++++---------------------------
> >> >> scripts/Makefile                 |  2 +-
> >> >> 8 files changed, 106 insertions(+), 53 deletions(-)
> >> >>
> >> >>diff --git a/include/linux/module.h b/include/linux/module.h
> >> >>index 188998d3dca9..aa56f531cf1e 100644
> >> >>--- a/include/linux/module.h
> >> >>+++ b/include/linux/module.h
> >> >>@@ -25,9 +25,6 @@
> >> >> #include <linux/percpu.h>
> >> >> #include <asm/module.h>
> >> >>
> >> >>-/* In stripped ARM and x86-64 modules, ~ is surprisingly rare. */
> >> >>-#define MODULE_SIG_STRING "~Module signature appended~\n"
> >> >>-    
> >> >
> >> > Hi Thiago, apologies for the delay.    
> >> 
> >> Hello Jessica, thanks for reviewing the patch!
> >>   
> >> > It looks like arch/s390/kernel/machine_kexec_file.c also relies on
> >> > MODULE_SIG_STRING being defined, so module_signature.h will need to be
> >> > included there too, otherwise we'll run into a compilation error.    
> >> 
> >> Indeed. Thanks for spotting that. The patch below fixes it. It's
> >> identical to the previous version except for the changes in 
> >> arch/s390/kernel/machine_kexec_file.c and their description in the
> >> commit message. I'm also copying some s390 people in this email.  
> >
> > to me the s390 part looks good but for one minor nit.  
> 
> Thanks for the prompt review!
> 
> > In arch/s390/Kconfig KEXEC_VERIFY_SIG currently depends on
> > SYSTEM_DATA_VERIFICATION. I'd prefer when you update this to the new
> > MODULE_SIG_FORMAT. It shouldn't make any difference right now, as we don't
> > use mod_check_sig in our code path. But it could cause problems in the future,
> > when more code might be shared.  
> 
> Makes sense. Here is the updated patch with the Kconfig change.
> 

The patch looks good now.

Thanks a lot
PHilipp