linux-kernel - Re: [PATCH v4 08/11] selftests/seccomp: Make kcmp() less required

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Message-ID: <202006160902.E331FF1917@keescook>
Date:   Tue, 16 Jun 2020 09:03:51 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Tycho Andersen <tycho@...ho.ws>
Cc:     linux-kernel@...r.kernel.org, Sargun Dhillon <sargun@...gun.me>,
        Christian Brauner <christian@...uner.io>,
        "David S. Miller" <davem@...emloft.net>,
        Christoph Hellwig <hch@....de>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Aleksa Sarai <cyphar@...har.com>,
        Matt Denton <mpdenton@...gle.com>,
        Jann Horn <jannh@...gle.com>, Chris Palmer <palmer@...gle.com>,
        Robert Sesek <rsesek@...gle.com>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, Shuah Khan <shuah@...nel.org>,
        netdev@...r.kernel.org, containers@...ts.linux-foundation.org,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 08/11] selftests/seccomp: Make kcmp() less required

On Tue, Jun 16, 2020 at 08:57:25AM -0600, Tycho Andersen wrote:
> On Mon, Jun 15, 2020 at 08:25:21PM -0700, Kees Cook wrote:
> > The seccomp tests are a bit noisy without CONFIG_CHECKPOINT_RESTORE (due
> > to missing the kcmp() syscall). The seccomp tests are more accurate with
> > kcmp(), but it's not strictly required. Refactor the tests to use
> > alternatives (comparing fd numbers), and provide a central test for
> > kcmp() so there is a single XFAIL instead of many. Continue to produce
> > warnings for the other tests, though.
> > 
> > Additionally adds some more bad flag EINVAL tests to the addfd selftest.
> > 
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> 
> This looks fine, but I wonder if this is enough motivation for taking
> kcmp() out of CONFIG_CHECKPOINT_RESTORE guards?

Do you mean in the kernel? I'd rather not -- it's a relatively powerful
primitive. Maybe if there were other users needing it, but there doesn't
seem to have been much demand.

-- 
Kees Cook