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

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Message-ID: <20160105183542.GD4617@pd.tnic>
Date:	Tue, 5 Jan 2016 19:35:42 +0100
From:	Borislav Petkov <bp@...e.de>
To:	Dave Hansen <dave@...1.net>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	dave.hansen@...ux.intel.com, hpa@...or.com, fenghua.yu@...el.com,
	yu-cheng.yu@...el.com
Subject: Re: [PATCH 1/5] x86: fix early command-line parsing when matching at
 end

On Tue, Dec 22, 2015 at 02:52:38PM -0800, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@...ux.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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