linux-kernel - Re: Modular BIG_KEYS (was: Re: [PATCH v4] security/keys: rewrite all of big

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Date:   Mon, 02 Oct 2017 22:12:04 +0100
From:   David Howells <dhowells@...hat.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     dhowells@...hat.com, "Jason A. Donenfeld" <Jason@...c4.com>,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
        kernel-hardening@...ts.openwall.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        ebiggers3@...il.com, Herbert Xu <herbert@...dor.apana.org.au>,
        Kirill Marinushkin <k.marinushkin@...il.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Ilhan Gurel <ilhan.gurel@...il.com>, security@...nel.org,
        stable <stable@...r.kernel.org>
Subject: Re: Modular BIG_KEYS (was: Re: [PATCH v4] security/keys: rewrite all of big_key crypto)

Geert Uytterhoeven <geert@...ux-m68k.org> wrote:

> Now this has hit mainline, the "BIG_KEYS" Kconfig symbol appeared on my
> radar. Is there any reason this cannot be tristate?

It was tristate, but it got converted to bool:

	commit 2eaf6b5dcafda2b8c22930eff7f48a364fce1741
	KEYS: Make BIG_KEYS boolean

and then:

	commit a1f2bdf338f15dbad10ee6362891ebf79244858b
	security/keys: make big_key.c explicitly non-modular

> So to save kernel size, I wan't to save N, but for a distro kernel that might
> have Kerberos users, you currently need to say Y, while M would be nicer.

If you want to do that, you'll need to implement demand-loading of key type
modules.

Note that you'd end up using a minimum of a whole page as a module rather than
~2K if built in (I know, that's a compromise you have to decide on).

David