linux-kernel - Re: [PATCH v15 2/3] virt: Add TDX guest driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <13adfc8d-8118-2fd7-3a66-98dfbf8037a9@linux.intel.com>
Date:   Fri, 21 Oct 2022 16:51:34 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Kai Huang <kai.huang@...el.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v15 2/3] virt: Add TDX guest driver

Hi Greg,

On 10/20/22 9:39 PM, Greg Kroah-Hartman wrote:
>>>> +#ifdef MODULE
>>>> +static const struct x86_cpu_id tdx_guest_ids[] = {
>>>> +	X86_MATCH_FEATURE(X86_FEATURE_TDX_GUEST, NULL),
>>>> +	{}
>>>> +};
>>>> +MODULE_DEVICE_TABLE(x86cpu, tdx_guest_ids);
>>>> +#endif
>>> Why the #ifdef?  Should not be needed, right?
>> I have added it to fix the following warning reported by 0-day.
>>
>> https://lore.kernel.org/lkml/202209211607.tCtTWKbV-lkp@intel.com/
>>
>> It is related to nullifying the MODULE_DEVICE_TABLE in #ifndef MODULE
>> case in linux/module.h.
> Then fix it properly, by correctly using that structure no matter what.
> You don't do that here...

I think we can use __maybe_unused attribute to fix this warning like
mentioned below. Are you fine with it?

--- a/drivers/virt/coco/tdx-guest/tdx-guest.c
+++ b/drivers/virt/coco/tdx-guest/tdx-guest.c
@@ -118,13 +118,11 @@ static void __exit tdx_guest_exit(void)
 }
 module_exit(tdx_guest_exit);
 
-#ifdef MODULE
-static const struct x86_cpu_id tdx_guest_ids[] = {
+static const struct x86_cpu_id __maybe_unused tdx_guest_ids[] = {
        X86_MATCH_FEATURE(X86_FEATURE_TDX_GUEST, NULL),
        {}
 };
 MODULE_DEVICE_TABLE(x86cpu, tdx_guest_ids);
-#endif

Solution 2:
-----------

We can also modify the code to use this structure in all cases like
below. But it requires me to use slower x86_match_cpu() in place of 
cpu_feature_enabled() which I think is unnecessary.

--- a/drivers/virt/coco/tdx-guest/tdx-guest.c
+++ b/drivers/virt/coco/tdx-guest/tdx-guest.c
@@ -103,9 +103,15 @@ static struct miscdevice tdx_misc_dev = {
        .fops = &tdx_guest_fops,
 };
 
+static const struct x86_cpu_id tdx_guest_ids[] = {
+       X86_MATCH_FEATURE(X86_FEATURE_TDX_GUEST, NULL),
+       {}
+};
+MODULE_DEVICE_TABLE(x86cpu, tdx_guest_ids);
+
 static int __init tdx_guest_init(void)
 {
-       if (!cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
+       if (!x86_match_cpu(tdx_guest_ids))
                return -ENODEV;
 
        return misc_register(&tdx_misc_dev);
@@ -118,14 +124,6 @@ static void __exit tdx_guest_exit(void)
 }
 module_exit(tdx_guest_exit);
 
-#ifdef MODULE
-static const struct x86_cpu_id tdx_guest_ids[] = {
-       X86_MATCH_FEATURE(X86_FEATURE_TDX_GUEST, NULL),
-       {}
-};
-MODULE_DEVICE_TABLE(x86cpu, tdx_guest_ids);
-#endif

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer