linux-kernel - Re: [PATCH] selinux: add __randomize_layout to selinux_audit

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Date:   Tue, 7 Jun 2022 16:05:31 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Gong Ruiqi <gongruiqi1@...wei.com>
Cc:     Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Kees Cook <keescook@...omium.org>, selinux@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Wang Weiyang <wangweiyang2@...wei.com>,
        Xiu Jianfeng <xiujianfeng@...wei.com>
Subject: Re: [PATCH] selinux: add __randomize_layout to selinux_audit_data

On Wed, May 18, 2022 at 12:03 PM Paul Moore <paul@...l-moore.com> wrote:
>
> On Wed, May 18, 2022 at 2:53 AM Gong Ruiqi <gongruiqi1@...wei.com> wrote:
> > On 2022/05/18 9:39, Paul Moore wrote:
> > > On Tue, May 17, 2022 at 9:21 PM GONG, Ruiqi <gongruiqi1@...wei.com> wrote:
> > >>
> > >> Randomize the layout of struct selinux_audit_data as suggested in [1],
> > >> since it contains a pointer to struct selinux_state, an already
> > >> randomized strucure.
> > >>
> > >> [1]: https://github.com/KSPP/linux/issues/188
> > >>
> > >> Signed-off-by: GONG, Ruiqi <gongruiqi1@...wei.com>
> > >> ---
> > >>  security/selinux/include/avc.h | 2 +-
> > >>  1 file changed, 1 insertion(+), 1 deletion(-)
> > >>
> > >> diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h
> > >> index 2b372f98f2d7..5525b94fd266 100644
> > >> --- a/security/selinux/include/avc.h
> > >> +++ b/security/selinux/include/avc.h
> > >> @@ -53,7 +53,7 @@ struct selinux_audit_data {
> > >>         u32 denied;
> > >>         int result;
> > >>         struct selinux_state *state;
> > >> -};
> > >> +} __randomize_layout;
> > >
> > > I'll apologize in advance for the stupid question, but does
> >
> > Not at all :)
> >
> > > __randomize_layout result in any problems when the struct is used in a
> > > trace event?  (see include/trace/events/avc.h)
> >
> > No, as least it doesn't in the testing I did. I believe we can use the
> > struct tagged with __randomize_layout as normal except that 1) it should
> > be initialized with a designated initializer, and 2) pointers to this
> > type can't be cast to/from pointers to another type. Other operations
> > like dereferencing members of the struct (as in
> > include/trace/events/avc.h) shouldn't be a problem.
> >
> > I did a testing to the patch on a qemu vm by running the selinux
> > testsuite with tracing events "avc:selinux_audited" enabled. The
> > testsuite completed successfully and from the tracing log I saw nothing
> > abnormal with my bare eyes. You can do more testing if you want or you
> > have other ideas of how to do so ;)
>
> That's great, thanks for verifying this.  I was aware of the other
> restrictions but wasn't sure about tracing.  Now I know :)
>
> It's too late to go into selinux/next for this dev cycle, but I'll
> queue this up for selinux/next once the merge window closes.

I just merged this into my local selinux/next branch and I'll be
pushing it up to the mail selinux tree later today - thanks!

-- 
paul-moore.com