linux-kernel - Does vdso_install attempt to re-compile objects under root privilege?

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Message-ID: <CAK7LNAQwHRJL=3yD_7P2mMSVnwZbayww+dHC22+v4oTpMZv58w@mail.gmail.com>
Date:   Wed, 3 Apr 2019 14:17:43 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        X86 ML <x86@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Does vdso_install attempt to re-compile objects under root privilege?

Hi.

I have a question about 'vdso_install'.

In my understanding, vdso is embedded in the kernel.
In addition, you can run 'make vdso_install'
to install an unstripped version of vdso.
(Mainly, debugging purpose?)

By default, 'make vdso_install' will install it to
/lib/modules/$(uname -r)/vdso/.

Since that directly is owned by root,
'make vdso_install' could potentially be
executed by root, isn't it?

Currently, 'vdso_install' depends on vdso,
so it may cause recompilation of objects
in the source tree.

This violates the basic rule:
"Installation targets must not modify the source tree".

We often miss this point. For example, see
commit 19514fc665ffbce624785f76ee7ad0ea6378a527

If this is a problem, I will fix Makefiles to
make 'vdso_install' not depend on vdso

Thanks.

-- 
Best Regards
Masahiro Yamada