Re: [ptxdist] [PATCH] kernel: do not strip signed modules

[Denis Osterland-Heim <denis.osterland@diehl.com>]

Hi,

Thanks for the input.

>$(mod_strip_cmd) $(2)/$(notdir $@) ; \
>$(mod_sign_cmd) $(2)/$(notdir $@) $(patsubst %,|| true,$(KBUILD_EXTMOD)) ; \
from scripts/Makefile.modinst

As far as I got it, with INSTALL_MOD_STRIP="--strip-debug -R .GCC.command.line" in KERNEL_MAKE_OPT
and always strip=n in targetinstall it should work identically with signed modules and without.

What do you and Marc think?

Regards, Denis

Am Dienstag, den 30.03.2021, 09:53 +0200 schrieb Michael Olbrich:
> On Tue, Mar 30, 2021 at 06:08:10AM +0000, Denis Osterland-Heim wrote:
> > If CONFIG_MODULE_SIG_ALL is set in kernelconfig then modules will be
> > automatically signed during the modules_install phase of a kernel build.
> >
> > Signed modules are BRITTLE as the signature is outside of the defined ELF
> > container. Thus they MAY NOT be stripped once the signature is computed
> > and attached. Note the entire module is the signed payload, including any
> > and all debug information present at the time of signing.
>
> Hmm, we had the same  issue at some point. The solution was a local copy of
> the shell code that does the stripping and installing. I think we added
> some code to sign the Modules again.
> The result was nice, but the whole thing was rather invasive and makes
> assumptions on how the module signing works internally in the kernel.
> So it was not something that I wanted to merge mainline that way.
>
> In general, I like this approach better. But there are two issues with it.
>
> 1. There are redundant options and if the uses gets it wrong then it wont
> fail at build time. We can get this from the kernelconfig:
> '$(shell ptxd_get_kconfig $(KERNEL_CONFIG) CONFIG_MODULE_SIG_ALL)' I think.
> But we have to make sure that it's not evaluated too early. To avoid
> slowing down ptxdist startup.
>
> 2. The modules are not stripped at all. So we should set
> INSTALL_MOD_STRIP=1 in this case.
>
> Marc, what do you think?
>
> Michael
>
> > See: https://www.kernel.org/doc/html/latest/admin-guide/module-signing.html
> > Signed-off-by: Denis Osterland-Heim <denis.osterland@diehl.com>
> > ---
> >  platforms/kernel.in | 7 +++++++
> >  rules/kernel.make   | 3 ++-
> >  2 files changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/platforms/kernel.in b/platforms/kernel.in
> > index 68899c0f7..8b9473b03 100644
> > --- a/platforms/kernel.in
> > +++ b/platforms/kernel.in
> > @@ -32,6 +32,13 @@ config KERNEL_MODULES
> >  default y
> >  prompt "build kernel-modules"
> >
> > +config KERNEL_MODULES_SIGNED
> > +bool "kernel-modules are signed on install"
> > +depends on KERNEL_MODULES
> > +help
> > +  Set this to y if CONFIG_MODULE_SIG_ALL is y in kernelconfig.
> > +  Otherwise the strip would damage automatically generated signature.
> > +
> >  config KERNEL_MODULES_INSTALL
> >  bool
> >  default y
> > diff --git a/rules/kernel.make b/rules/kernel.make
> > index ea748fc8a..c964bd672 100644
> > --- a/rules/kernel.make
> > +++ b/rules/kernel.make
> > @@ -313,7 +313,8 @@ ifdef PTXCONF_KERNEL_MODULES_INSTALL
> >  @$(call install_fixup, kernel-modules, AUTHOR,"Robert Schwebel <r.schwebel@pengutronix.de>")
> >  @$(call install_fixup, kernel-modules, DESCRIPTION,missing)
> >
> > -@$(call install_glob, kernel-modules, 0, 0, -, /lib/modules, *.ko,, k)
> > +@$(call install_glob, kernel-modules, 0, 0, -, /lib/modules, *.ko,, \
> > +$(call ptx/ifdef,PTXCONF_KERNEL_MODULES_SIGNED,n,k))
> >  @$(call install_glob, kernel-modules, 0, 0, -, /lib/modules,, *.ko */build */source, n)
> >
> >  @$(call install_finish, kernel-modules)
> > --
> > 2.31.1
> >
> > _______________________________________________
> > ptxdist mailing list
> > ptxdist@pengutronix.de
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