Re: [OE-core] [RFC PATCH] kernel: Add kernel-cve-tool support to help monitor kernel CVEs

[<Mikko.Rapeli@bmw.de>]

On Mon, Mar 21, 2022 at 10:37:17AM +0000, Richard Purdie wrote:
> On Mon, 2022-03-21 at 07:48 +0000, Mikko.Rapeli@bmw.de wrote:
> > Hi,
> > 
> > Thanks for the interesting patch!
> > 
> > On Sat, Mar 19, 2022 at 07:25:55PM +0000, Richard Purdie wrote:
> > > This adds support for a random kernel CVE monitoring tool which can be
> > > run as a specific task against a kernel:
> > > 
> > > $ bitbake linux-yocto -c checkcves
> > > [...]
> > > Sstate summary: Wanted 3 Local 3 Mirrors 0 Missed 0 Current 135 (100% match, 100% complete)
> > > NOTE: Executing Tasks
> > > WARNING: linux-yocto-5.15.26+gitAUTOINC+ea948a0983_5bd4bda819-r0 do_checkcves: Should consider cherry-pick for be80a1d3f9dbe5aee79a325964f7037fe2d92f30:CVE-2021-4204 (NOT FOR THIS VERSION)
> > > WARNING: linux-yocto-5.15.26+gitAUTOINC+ea948a0983_5bd4bda819-r0 do_checkcves: Should consider cherry-pick for 20b2aff4bc15bda809f994761d5719827d66c0b4:CVE-2022-0500 (NOT FOR THIS VERSION)
> > > WARNING: linux-yocto-5.15.26+gitAUTOINC+ea948a0983_5bd4bda819-r0 do_checkcves: Should consider cherry-pick for 55749769fe608fa3f4a075e42e89d237c8e37637:CVE-2021-4095 (NOT FOR THIS VERSION)
> > > WARNING: linux-yocto-5.15.26+gitAUTOINC+ea948a0983_5bd4bda819-r0 do_checkcves: Should consider cherry-pick for 4fbcc1a4cb20fe26ad0225679c536c80f1648221:CVE-2022-26490 (NOT FOR THIS VERSION)
> > > WARNING: linux-yocto-5.15.26+gitAUTOINC+ea948a0983_5bd4bda819-r0 do_checkcves: Should consider cherry-pick for dbbf2d1e4077bab0c65ece2765d3fc69cf7d610f:CVE-2019-15239 (NOT FOR THIS VERSION)
> > > WARNING: linux-yocto-5.15.26+gitAUTOINC+ea948a0983_5bd4bda819-r0 do_checkcves: Should consider cherry-pick for 89f3594d0de58e8a57d92d497dea9fee3d4b9cda:CVE-2022-24958 (NOT FOR THIS VERSION)
> > > WARNING: linux-yocto-5.15.26+gitAUTOINC+ea948a0983_5bd4bda819-r0 do_checkcves: Should consider cherry-pick for 1bfba2f4270c64c912756fc76621bbce959ddf2e:CVE-2020-25220 (NOT FOR THIS VERSION)
> > > NOTE: Tasks Summary: Attempted 627 tasks of which 626 didn't need to be rerun and all succeeded.
> > > 
> > > Posted as an RFC to see what people think of this. I make no claims
> > > on how useful it is/isn't but wanted to show integration isn't difficult
> > > and provide some inspiration for ideas.
> > > 
> > > Details on the tool in question: https://github.com/madisongh/kernel-cve-tool
> > > 
> > > I've ignored the NO-FIXES-AVILABLE and PATCHED-CVES files.
> > > 
> > > Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
> > > ---
> > >  meta/classes/kernel.bbclass                   | 10 ++++++++++
> > >  .../kernel-cve-tool/kernel-cve-tool_git.bb    | 20 +++++++++++++++++++
> > >  2 files changed, 30 insertions(+)
> > >  create mode 100644 meta/recipes-kernel/kernel-cve-tool/kernel-cve-tool_git.bb
> > > 
> > > diff --git a/meta/classes/kernel.bbclass b/meta/classes/kernel.bbclass
> > > index 4f304eb9c7a..a842747b9d9 100644
> > > --- a/meta/classes/kernel.bbclass
> > > +++ b/meta/classes/kernel.bbclass
> > > @@ -753,6 +753,16 @@ addtask sizecheck before do_install after do_strip
> > >  
> > >  inherit kernel-artifact-names
> > >  
> > > +do_checkcves () {
> > > +	cd ${S}
> > > +	kernel-cve-tool -P ${STAGING_DATADIR_NATIVE}/kernel-cvedb
> > > +	while read -r line; do 
> > > +		bbwarn "Should consider cherry-pick for $line"; 
> > 
> > cherry-picking isn't recommended. Instead, stable releases should be merged
> > fully into product trees to fix CVE and other critical bugs.
> > 
> > cherry-picking will miss bugs which don't yet have CVEs or exploits.
> > cherry-picking will also miss non-obvious patch dependencies.
> > 
> > Kernel community including Android documentation strongly recommends
> > stable tree merges.
> 
> If you have a stable tree available!

As a git remote you always will. If you get a BSP Linux kernel without
git version history, well you and your vendors are doing it all wrong.

It is always possible to merge stable tree releases into vendor trees.

The amount of hacks in vendor trees can make this hard, e.g. merge conflicts, but
it is still the best practice which will be better in the long term instead of
cherry-picking only CVE fixes.

> > https://source.android.com/devices/architecture/kernel/releases#keeping-a-
> > secure-system
> > 
> > "When deploying a device that uses Linux, it is strongly recommended that all
> > LTS kernel updates be taken by the manufacturer and pushed out to their users
> > after proper testing shows the update works well"
> > 
> > http://kroah.com/log/blog/2018/02/05/linux-kernel-release-model/
> > 
> > "When deploying a device that uses Linux, it is strongly recommended that all
> > LTS kernel updates be taken by the manufacturer and pushed out to their users
> > after proper testing shows the update works well. As was described above, it
> > is not wise to try to pick and choose various patches from the LTS
> > releases..."
> > 
> > I think the cherry-pick status is not useful, but the list of CVEs and patches
> > to various subsystems is useful to users. IMO the tool should ask for a point
> > release merge from upstream instead.
> 
> I think a lot depends on the scenario you're using this in. The different ouputs
> are useful in different scenarios...

I'm sorry but really, there isn't anything else which will work in the long run.
If anyone proposes cherry-picking Linux kernel CVE patches, they are doing it wrong.

> > 
> > > +	done < ${S}/cherry-picks.list
> > > +}
> > > +do_checkcves[depends] = "kernel-cve-tool-native:do_populate_sysroot"
> > > +addtask checkcves after do_configure
> > > +
> > >  kernel_do_deploy() {
> > >  	deployDir="${DEPLOYDIR}"
> > >  	if [ -n "${KERNEL_DEPLOYSUBDIR}" ]; then
> > > diff --git a/meta/recipes-kernel/kernel-cve-tool/kernel-cve-tool_git.bb b/meta/recipes-kernel/kernel-cve-tool/kernel-cve-tool_git.bb
> > > new file mode 100644
> > > index 00000000000..d2402bae052
> > > --- /dev/null
> > > +++ b/meta/recipes-kernel/kernel-cve-tool/kernel-cve-tool_git.bb
> > > @@ -0,0 +1,20 @@
> > > +HOMEPAGE = "https://github.com/madisongh/kernel-cve-tool/"
> > > +SRC_URI = "git://github.com/madisongh/kernel-cve-tool;protocol=https;branch=master;name=tool \
> > > +           git://github.com/nluedtke/linux_kernel_cves.git;protocol=https;branch=master;destsuffix=cvedb;name=data"
> > 
> > Could the 'data' be handled like the CVE database and updated regularly/automatically?
> 
> Something like:
> 
> SRCREV_data = "${AUTOREV}"
> 
> should do that. In some ways I prefer this to the CVE database approach since
> you always have a deterministic outcome for a given revision.

Yep, good to know.

Cheers,

-Mikko