linux-kernel - [tip:x86/urgent] x86, smap: Don' t enable SMAP if CONFIG_X86

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Message-ID: <tip-03bbd596ac04fef47ce93a730b8f086d797c3021@git.kernel.org>
Date:	Thu, 13 Feb 2014 07:54:28 -0800
From:	"tip-bot for H. Peter Anvin" <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	tglx@...utronix.de, fengguang.wu@...el.com, hpa@...ux.intel.com
Subject: [tip:x86/urgent] x86, smap: Don'
 t enable SMAP if CONFIG_X86_SMAP is disabled

Commit-ID:  03bbd596ac04fef47ce93a730b8f086d797c3021
Gitweb:     http://git.kernel.org/tip/03bbd596ac04fef47ce93a730b8f086d797c3021
Author:     H. Peter Anvin <hpa@...ux.intel.com>
AuthorDate: Thu, 13 Feb 2014 07:34:30 -0800
Committer:  H. Peter Anvin <hpa@...ux.intel.com>
CommitDate: Thu, 13 Feb 2014 07:50:25 -0800

x86, smap: Don't enable SMAP if CONFIG_X86_SMAP is disabled

If SMAP support is not compiled into the kernel, don't enable SMAP in
CR4 -- in fact, we should clear it, because the kernel doesn't contain
the proper STAC/CLAC instructions for SMAP support.

Found by Fengguang Wu's test system.

Reported-by: Fengguang Wu <fengguang.wu@...el.com>
Link: http://lkml.kernel.org/r/20140213124550.GA30497@localhost
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
Cc: <stable@...r.kernel.org> # v3.7+
---
 arch/x86/kernel/cpu/common.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 24b6fd1..8e28bf2 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -284,8 +284,13 @@ static __always_inline void setup_smap(struct cpuinfo_x86 *c)
 	raw_local_save_flags(eflags);
 	BUG_ON(eflags & X86_EFLAGS_AC);
 
-	if (cpu_has(c, X86_FEATURE_SMAP))
+	if (cpu_has(c, X86_FEATURE_SMAP)) {
+#ifdef CONFIG_X86_SMAP
 		set_in_cr4(X86_CR4_SMAP);
+#else
+		clear_in_cr4(X86_CR4_SMAP);
+#endif
+	}
 }
 
 /*
--
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