[tip:x86/urgent] x86, smap: Don' t enable SMAP if CONFIG_X86_SMAP is disabled

tip-bot for H. Peter Anvin
2014-02-13T15:54:45Z

Commit-ID: 03bbd596ac04fef47ce93a730b8f086d797c3021
Gitweb: http://git.kernel.org/tip/03bbd596ac04fef47ce93a730b8f086d797c3021
Author: H. Peter Anvin <hpa@linux.intel.com>
AuthorDate: Thu, 13 Feb 2014 07:34:30 -0800
Committer: H. Peter Anvin <hpa@linux.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@intel.com>
Link: http://lkml.kernel.org/r/20140213124550.GA30497@localhost
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: <stable@vger.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
+ }
}

/*