linux-kernel - Re: [PATCH] x86/cpu/amd: Report zenbleed in sysfs

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Date:   Fri, 28 Jul 2023 16:14:25 -0700
From:   Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To:     Nikolay Borisov <nik.borisov@...e.com>
Cc:     x86@...nel.org, bp@...en8.de, tglx@...utronix.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/cpu/amd: Report zenbleed in sysfs

On Thu, Jul 27, 2023 at 10:54:46AM +0300, Nikolay Borisov wrote:
> Initial submission of Zenbleed fix omitted reporting the bug in sysfs.
> There's no reason why it shouldn't be reported so let's add it among
> the other vulnerabilities.
> 
> Signed-off-by: Nikolay Borisov <nik.borisov@...e.com>
> ---
>  .../ABI/testing/sysfs-devices-system-cpu          |  1 +
>  arch/x86/kernel/cpu/amd.c                         | 15 +++++++++++++++
>  drivers/base/cpu.c                                |  8 ++++++++
>  include/linux/cpu.h                               |  2 ++
>  4 files changed, 26 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index ecd585ca2d50..30bb4196e451 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -524,6 +524,7 @@ What:		/sys/devices/system/cpu/vulnerabilities
>  		/sys/devices/system/cpu/vulnerabilities/itlb_multihit
>  		/sys/devices/system/cpu/vulnerabilities/mmio_stale_data
>  		/sys/devices/system/cpu/vulnerabilities/retbleed
> +		/sys/devices/system/cpu/vulnerabilities/zenbleed
>  Date:		January 2018
>  Contact:	Linux kernel mailing list <linux-kernel@...r.kernel.org>
>  Description:	Information about CPU vulnerabilities
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index 26ad7ca423e7..3ab9745eafc5 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -1279,6 +1279,21 @@ u32 amd_get_highest_perf(void)
>  }
>  EXPORT_SYMBOL_GPL(amd_get_highest_perf);
>  
> +ssize_t cpu_show_zenbleed(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +

Extra newline.

> +	if (!cpu_has_amd_erratum(&boot_cpu_data, amd_zenbleed) ||
> +	    !boot_cpu_has(X86_FEATURE_AVX) ||
> +	    boot_cpu_has(X86_FEATURE_HYPERVISOR))
> +		return sysfs_emit(buf, "Not affected\n");
> +
> +	if (!cpu_has_zenbleed_microcode()) {

For readability this can check of microcode present case, and drop the
NOT operator.

> +		return sysfs_emit(buf, "Mitigation: Chickenbit\n");

Shouldn't this be checking if the chicken bit is set? And if its not set
then report "Vulnerable".

But, looking at zenbleed_check() it appear that the chicken bit for
zenbleed will always be present, and it will always be set if microcode
is not present.

> +	} else {
> +		return sysfs_emit(buf, "Mitigation: Microcode\n");
> +	}
> +}