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

[Nikolay Borisov]

On 29.07.23 г. 2:14 ч., Pawan Gupta wrote:
> 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@xxxxxxxx>
> > ---
> >   .../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@xxxxxxxxxxxxxxx>
> >   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.

Yeah, but based on feedback I got from Boris it seems this is not going 
to be merged so it doesn't matter.

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