From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "Paul Durrant" <paul@xen.org>,
Xen-devel <xen-devel@lists.xenproject.org>,
"Roger Pau Monné" <roger.pau@citrix.com>, "Wei Liu" <wl@xen.org>,
"Ian Jackson" <Ian.Jackson@citrix.com>
Subject: Re: [PATCH 9/9] x86/spec-ctrl: Hide RDRAND by default on IvyBridge
Date: Wed, 17 Jun 2020 12:39:35 +0200 [thread overview]
Message-ID: <bc5d43b4-afbc-0732-b24f-2edfa939a961@suse.com> (raw)
In-Reply-To: <00db98fd-d268-71ae-fad1-fb59d2f1eba1@citrix.com>
On 16.06.2020 18:26, Andrew Cooper wrote:
> On 16/06/2020 11:00, Jan Beulich wrote:
>> On 15.06.2020 16:15, Andrew Cooper wrote:
>>> --- a/tools/libxc/xc_cpuid_x86.c
>>> +++ b/tools/libxc/xc_cpuid_x86.c
>>> @@ -503,6 +503,9 @@ int xc_cpuid_apply_policy(xc_interface *xch, uint32_t domid, bool restore,
>>> */
>>> if ( restore )
>>> {
>>> + if ( test_bit(X86_FEATURE_RDRAND, host_featureset) && !p->basic.rdrand )
>>> + p->basic.rdrand = true;
>> Same question as before: Why do you derive from the host feature set rather
>> than the domain type's maximum one?
>
> Answer the same as previous.
>
> Although I do see now that this should be simplified to:
>
> p->basic.rdrand = test_bit(X86_FEATURE_RDRAND, host_featureset);
>
> which I've done.
Right. It makes even more noticeable though that this may mean a
new feature suddenly appearing after the guest was migrated. But
aiui this still is the default behavior for all features anyway.
>>> --- a/xen/arch/x86/cpuid.c
>>> +++ b/xen/arch/x86/cpuid.c
>>> @@ -340,6 +340,25 @@ static void __init calculate_host_policy(void)
>>> }
>>> }
>>>
>>> +static void __init guest_common_default_feature_adjustments(uint32_t *fs)
>>> +{
>>> + /*
>>> + * IvyBridge client parts suffer from leakage of RDRAND data due to SRBDS
>>> + * (XSA-320 / CVE-2020-0543), and won't be receiving microcode to
>>> + * compensate.
>>> + *
>>> + * Mitigate by hiding RDRAND from guests by default, unless explicitly
>>> + * overridden on the Xen command line (cpuid=rdrand). Irrespective of the
>>> + * default setting, guests can use RDRAND if explicitly enabled
>>> + * (cpuid="host,rdrand=1") in the VM's config file, and VMs which were
>>> + * previously using RDRAND can migrate in.
>>> + */
>>> + if ( boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
>>> + boot_cpu_data.x86 == 6 && boot_cpu_data.x86_model == 0x3a &&
>> This is the first time (description plus patch so far) that the issue
>> gets mentioned to be for and the workaround restricted to client parts
>> only. If so, I think at least the doc should say so too.
>
> I've updated the command line doc, and patch subject.
Thanks - with the adjustments
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Jan
next prev parent reply other threads:[~2020-06-17 10:39 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-15 14:15 [PATCH for-4.14 0/9] XSA-320 follow for IvyBridge Andrew Cooper
2020-06-15 14:15 ` [PATCH 1/9] tools/libx[cl]: Introduce struct xc_xend_cpuid for xc_cpuid_set() Andrew Cooper
2020-06-15 14:51 ` Ian Jackson
2020-06-15 14:15 ` [PATCH 2/9] tests/cpu-policy: Confirm that CPUID serialisation is sorted Andrew Cooper
2020-06-15 14:52 ` Ian Jackson
2020-06-15 15:00 ` Andrew Cooper
2020-06-15 15:34 ` Ian Jackson
2020-06-15 16:12 ` Andrew Cooper
2020-06-16 6:51 ` Jan Beulich
2020-06-16 9:01 ` Jan Beulich
2020-06-15 14:15 ` [PATCH 3/9] tools/libx[cl]: Move processing loop down into xc_cpuid_set() Andrew Cooper
2020-06-15 14:54 ` Ian Jackson
2020-06-16 9:16 ` Jan Beulich
2020-06-16 15:58 ` Andrew Cooper
2020-06-15 14:15 ` [PATCH 4/9] tools/libx[cl]: Merge xc_cpuid_set() into xc_cpuid_apply_policy() Andrew Cooper
2020-06-15 14:55 ` Ian Jackson
2020-06-15 14:15 ` [PATCH 5/9] tools/libx[cl]: Plumb bool restore down " Andrew Cooper
2020-06-15 14:55 ` Ian Jackson
2020-06-15 14:15 ` [PATCH 6/9] x86/gen-cpuid: Distinguish default vs max in feature annotations Andrew Cooper
2020-06-15 14:15 ` [PATCH 7/9] x86/hvm: Disable MPX by default Andrew Cooper
2020-06-16 9:33 ` Jan Beulich
2020-06-16 16:15 ` Andrew Cooper
2020-06-17 10:32 ` Jan Beulich
2020-06-17 11:16 ` Andrew Cooper
2020-06-17 11:24 ` Jan Beulich
2020-06-17 11:28 ` Andrew Cooper
2020-06-17 11:41 ` Jan Beulich
2020-06-17 11:47 ` Andrew Cooper
2020-06-15 14:15 ` [PATCH 8/9] x86/cpuid: Introduce missing feature adjustment in calculate_pv_def_policy() Andrew Cooper
2020-06-16 9:40 ` Jan Beulich
2020-06-16 16:17 ` Andrew Cooper
2020-06-15 14:15 ` [PATCH 9/9] x86/spec-ctrl: Hide RDRAND by default on IvyBridge Andrew Cooper
2020-06-16 10:00 ` Jan Beulich
2020-06-16 16:26 ` Andrew Cooper
2020-06-17 10:39 ` Jan Beulich [this message]
2020-06-17 11:21 ` Andrew Cooper
2020-06-15 17:04 ` [PATCH for-4.14 0/9] XSA-320 follow for IvyBridge Paul Durrant
2020-06-17 12:46 ` Paul Durrant
2020-06-18 7:18 ` Jan Beulich
2020-06-18 9:37 ` Andrew Cooper
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