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@linux.intel.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: x86@kernel.org
Link: http://lkml.kernel.org/r/20141111220133.FE053984@viggo.jf.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index ca93cc79fbc665968b76c561b4ef0a33f53c11f2..6284d6dce038933212efb096944c62363e464af6 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -140,6 +140,8 @@ 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);
        return 1;