linux-kernel - [tip:x86/pti] x86/pti: Disallow global kernel text with RANDSTRUCT

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Date:   Tue, 24 Apr 2018 01:08:37 -0700
From:   tip-bot for Dave Hansen <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     vbabka@...e.cz, torvalds@...ux-foundation.org, jgross@...e.com,
        tglx@...utronix.de, peterz@...radead.org, hughd@...gle.com,
        aarcange@...hat.com, dan.j.williams@...el.com, jpoimboe@...hat.com,
        namit@...are.com, gregkh@...uxfoundation.org, dwmw2@...radead.org,
        arjan@...ux.intel.com, linux-kernel@...r.kernel.org,
        luto@...nel.org, dave.hansen@...ux.intel.com, mingo@...nel.org,
        keescook@...gle.com, bp@...en8.de, hpa@...or.com
Subject: [tip:x86/pti] x86/pti: Disallow global kernel text with RANDSTRUCT

Commit-ID:  26d35ca6c3776784f8156e1d6f80cc60d9a2a915
Gitweb:     https://git.kernel.org/tip/26d35ca6c3776784f8156e1d6f80cc60d9a2a915
Author:     Dave Hansen <dave.hansen@...ux.intel.com>
AuthorDate: Fri, 20 Apr 2018 15:20:26 -0700
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Tue, 24 Apr 2018 09:50:54 +0200

x86/pti: Disallow global kernel text with RANDSTRUCT

RANDSTRUCT derives its hardening benefits from the attacker's lack of
knowledge about the layout of kernel data structures.  Keep the kernel
image non-global in cases where RANDSTRUCT is in use to help keep the
layout a secret.

Fixes: 8c06c7740 (x86/pti: Leave kernel text global for !PCID)
Reported-by: Kees Cook <keescook@...gle.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Ingo Molnar <mingo@...nel.org>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: linux-mm@...ck.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Nadav Amit <namit@...are.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Link: https://lkml.kernel.org/r/20180420222026.D0B4AAC9@viggo.jf.intel.com

---
 arch/x86/mm/pti.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index ae3eb4f5d53b..4d418e705878 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -421,6 +421,16 @@ static inline bool pti_kernel_image_global_ok(void)
 	if (boot_cpu_has(X86_FEATURE_K8))
 		return false;
 
+	/*
+	 * RANDSTRUCT derives its hardening benefits from the
+	 * attacker's lack of knowledge about the layout of kernel
+	 * data structures.  Keep the kernel image non-global in
+	 * cases where RANDSTRUCT is in use to help keep the layout a
+	 * secret.
+	 */
+	if (IS_ENABLED(CONFIG_GCC_PLUGIN_RANDSTRUCT))
+		return false;
+
 	return true;
 }