[3.16.y-ckt stable] Patch "x86: Require exact match for 'noxsave' command line option" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    x86: Require exact match for 'noxsave' command line option

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt3.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 722d19de067ab6a61dd105213f8aa3508917d75b Mon Sep 17 00:00:00 2001
From: Dave Hansen <dave.hansen at linux.intel.com>
Date: Tue, 11 Nov 2014 14:01:33 -0800
Subject: x86: Require exact match for 'noxsave' command line option

commit 2cd3949f702692cf4c5d05b463f19cd706a92dd3 upstream.

We have some very similarly named command-line options:

arch/x86/kernel/cpu/common.c:__setup("noxsave", x86_xsave_setup);
arch/x86/kernel/cpu/common.c:__setup("noxsaveopt", x86_xsaveopt_setup);
arch/x86/kernel/cpu/common.c:__setup("noxsaves", x86_xsaves_setup);

__setup() is designed to match options that take arguments, like
"foo=bar" where you would have:

	__setup("foo", x86_foo_func...);

The problem is that "noxsave" actually _matches_ "noxsaves" in
the same way that "foo" matches "foo=bar".  If you boot an old
kernel that does not know about "noxsaves" with "noxsaves" on the
command line, it will interpret the argument as "noxsave", which
is not what you want at all.

This makes the "noxsave" handler only return success when it finds
an *exact* match.

[ tglx: We really need to make __setup() more robust. ]

Signed-off-by: Dave Hansen <dave.hansen at linux.intel.com>
Cc: Dave Hansen <dave at sr71.net>
Cc: Fenghua Yu <fenghua.yu at intel.com>
Cc: x86 at kernel.org
Link: http://lkml.kernel.org/r/20141111220133.FE053984@viggo.jf.intel.com
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/x86/kernel/cpu/common.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index ae52a082a01c..1f3a8885f836 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -146,6 +146,8 @@ EXPORT_PER_CPU_SYMBOL_GPL(gdt_page);

 static int __init x86_xsave_setup(char *s)
 {
+	if (strlen(s))
+		return 0;
 	setup_clear_cpu_cap(X86_FEATURE_XSAVE);
 	setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
 	setup_clear_cpu_cap(X86_FEATURE_AVX);
--
2.1.0