linux-kernel - [PATCH 3.12 43/82] x86, smap: Dont enable SMAP if CONFIG_X86

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Message-Id: <20140220235020.762281188@linuxfoundation.org>
Date:	Thu, 20 Feb 2014 15:52:26 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Fengguang Wu <fengguang.wu@...el.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: [PATCH 3.12 43/82] x86, smap: Dont enable SMAP if CONFIG_X86_SMAP is disabled

3.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "H. Peter Anvin" <hpa@...ux.intel.com>

commit 03bbd596ac04fef47ce93a730b8f086d797c3021 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kernel/cpu/common.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -284,8 +284,13 @@ static __always_inline void setup_smap(s
 	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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