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

[tip-bot for Dave Hansen]

Commit-ID:  b7c21bc56fbedf4a61b628c6b11e0d7048746cc1
Gitweb:     https://git.kernel.org/tip/b7c21bc56fbedf4a61b628c6b11e0d7048746cc1
Author:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
AuthorDate: Fri, 20 Apr 2018 15:20:26 -0700
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Wed, 25 Apr 2018 11:02:51 +0200

x86/pti: Disallow global kernel text with RANDSTRUCT

commit 26d35ca6c3776784f8156e1d6f80cc60d9a2a915

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@xxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Nadav Amit <namit@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Link: https://lkml.kernel.org/r/20180420222026.D0B4AAC9@xxxxxxxxxxxxxxxxxx


---
 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;
 }