linux-kernel - [PATCH bpf-next v2 07/10] bpf: lsm: Make the allocated callback RO+X

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Message-Id: <20200115171333.28811-8-kpsingh@chromium.org>
Date:   Wed, 15 Jan 2020 18:13:30 +0100
From:   KP Singh <kpsingh@...omium.org>
To:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        linux-security-module@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        James Morris <jmorris@...ei.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Garnier <thgarnie@...omium.org>,
        Michael Halcrow <mhalcrow@...gle.com>,
        Paul Turner <pjt@...gle.com>,
        Brendan Gregg <brendan.d.gregg@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Christian Brauner <christian@...uner.io>,
        Mickaël Salaün <mic@...ikod.net>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Quentin Monnet <quentin.monnet@...ronome.com>,
        Andrey Ignatov <rdna@...com>, Joe Stringer <joe@...d.net.nz>
Subject: [PATCH bpf-next v2 07/10] bpf: lsm: Make the allocated callback RO+X

From: KP Singh <kpsingh@...gle.com>

This patch is not needed after arch_bpf_prepare_trampoline
moves to using text_poke.

The two IPI TLB flushes can be further optimized if a new API to handle
W^X in the kernel emerges as an outcome of:

  https://lore.kernel.org/bpf/20200103234725.22846-1-kpsingh@chromium.org/

Signed-off-by: KP Singh <kpsingh@...gle.com>
---
 security/bpf/hooks.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
index 4e71da0e8e9e..30f68341f5ef 100644
--- a/security/bpf/hooks.c
+++ b/security/bpf/hooks.c
@@ -222,6 +222,15 @@ static struct bpf_lsm_hook *bpf_lsm_hook_alloc(
 		goto error;
 	}
 
+	/* First make the page read-only, and only then make it executable to
+	 * prevent it from being W+X in between.
+	 */
+	set_memory_ro((unsigned long)image, 1);
+	/* More checks can be done here to ensure that nothing was changed
+	 * between arch_prepare_bpf_trampoline and set_memory_ro.
+	 */
+	set_memory_x((unsigned long)image, 1);
+
 	hook = kzalloc(sizeof(struct bpf_lsm_hook), GFP_KERNEL);
 	if (!hook) {
 		ret = -ENOMEM;
-- 
2.20.1