Re: [PATCH 1/5] x86: fix early command-line parsing when matching at end

Borislav Petkov
2016-01-05T18:35:49Z

On Tue, Dec 22, 2015 at 02:52:38PM -0800, Dave Hansen wrote:
>
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> The x86 early command line parsing in cmdline_find_option_bool()
> is buggy. If it matches a specified 'option' all the way to
> the end of the command-line, it will consider it a match.
>
> For instance,
>
> cmdline = "foo";
> cmdline_find_option_bool(cmdline, "fool");
>
> will return 1. This is particularly annoying since we have
> actual FPU options like "noxsave" and "noxsaves" So,
> command-line "foo bar noxsave" will match *BOTH* a "noxsave" and
> "noxsaves". (This turns out not to be an actual problem because
> "noxsave" implies "noxsaves", but it's still confusing.)

So I booted a guest with this command line:

[ 0.000000] Kernel command line: root=/dev/sda1 resume=/dev/sdb1 debug ignore_loglevel log_buf_len=16M earlyprintk=ttyS0,115200 console=ttyS0,115200 console=tty0 noxsave

after applying the debug hunk below. However, the only debug output I
got is this:

[ 0.000000] x86_noxsave_setup

If I supply "noxsaves", I get, as expected

[ 0.000000] x86_noxsaves_setup

only. Ditto for "noxsaveopt".

So what am I missing?

---
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 1a6adcb4fbce..472f6edfb8d9 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -354,6 +354,8 @@ static int __init x86_noxsave_setup(char *s)
if (strlen(s))
return 0;

+ pr_info("%s\n", __func__);
+
fpu__xstate_clear_all_cpu_caps();

return 1;
@@ -367,6 +369,8 @@ static int __init x86_noxsaveopt_setup(char *s)
{
setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);

+ pr_info("%s\n", __func__);
+
return 1;
}
__setup("noxsaveopt", x86_noxsaveopt_setup);
@@ -378,6 +382,8 @@ static int __init x86_noxsaves_setup(char *s)
{
setup_clear_cpu_cap(X86_FEATURE_XSAVES);

+ pr_info("%s\n", __func__);
+
return 1;
}
__setup("noxsaves", x86_noxsaves_setup);

--
Regards/Gruss,
Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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