On Thu, Jul 14, 2022 at 06:30:18PM -0700, Pawan Gupta wrote:
> Older CPUs beyond its Servicing period are not listed in the affected
> processor list for MMIO Stale Data vulnerabilities. These CPUs currently
> report "Not affected" in sysfs, which may not be correct.
>
> Add support for "Unknown" reporting for such CPUs. Mitigation is not
> deployed when the status is "Unknown".
>
> "CPU is beyond its Servicing period" means these CPUs are beyond their
> Servicing [1] period and have reached End of Servicing Updates (ESU) [2].
>
> [1] Servicing: The process of providing functional and security
> updates to Intel processors or platforms, utilizing the Intel Platform
> Update (IPU) process or other similar mechanisms.
>
> [2] End of Servicing Updates (ESU): ESU is the date at which Intel
> will no longer provide Servicing, such as through IPU or other similar
> update processes. ESU dates will typically be aligned to end of
> quarter.
The explanations of those things need to be...
> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Suggested-by: Tony Luck <tony.luck@xxxxxxxxx>
> Fixes: 8d50cdf8b834 ("x86/speculation/mmio: Add sysfs reporting for Processor MMIO Stale Data")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
> ---
> CPU vulnerability is unknown if, hardware doesn't set the immunity bits
> and CPU is not in the known-affected-list.
>
> In order to report the unknown status, this patch sets the MMIO bug
> for all Intel CPUs that don't have the hardware immunity bits set.
> Based on the known-affected-list of CPUs, mitigation selection then
> deploys the mitigation or sets the "Unknown" status; which is ugly.
>
> I will appreciate suggestions to improve this.
>
> Thanks,
> Pawan
>
> .../hw-vuln/processor_mmio_stale_data.rst | 3 +++
> arch/x86/kernel/cpu/bugs.c | 11 +++++++-
> arch/x86/kernel/cpu/common.c | 26 +++++++++++++------
> arch/x86/kernel/cpu/cpu.h | 1 +
> 4 files changed, 32 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst b/Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
> index 9393c50b5afc..55524e0798da 100644
> --- a/Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
> +++ b/Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
> @@ -230,6 +230,9 @@ The possible values in this file are:
> * - 'Mitigation: Clear CPU buffers'
> - The processor is vulnerable and the CPU buffer clearing mitigation is
> enabled.
> + * - 'Unknown: CPU is beyond its Servicing period'
> + - The processor vulnerability status is unknown because it is
> + out of Servicing period. Mitigation is not attempted.
... here.
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 736262a76a12..82088410870e 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1286,6 +1286,22 @@ static bool arch_cap_mmio_immune(u64 ia32_cap)
> ia32_cap & ARCH_CAP_SBDR_SSDP_NO);
> }
>
> +bool __init mmio_stale_data_unknown(void)
This function need to go to ...cpu/intel.c
> +{
> + u64 ia32_cap = x86_read_arch_cap_msr();
> +
> + if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
> + return false;
<---- newline here.
> + /*
> + * CPU vulnerability is unknown when, hardware doesn't set the
no comma after the "when"
> + * immunity bits and CPU is not in the known affected list.
> + */
> + if (!cpu_matches(cpu_vuln_blacklist, MMIO) &&
> + !arch_cap_mmio_immune(ia32_cap))
> + return true;
<---- newline here.
> + return false;
> +}
> +
> static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
> {
> u64 ia32_cap = x86_read_arch_cap_msr();
> @@ -1349,14 +1365,8 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
> cpu_matches(cpu_vuln_blacklist, SRBDS | MMIO_SBDS))
> setup_force_cpu_bug(X86_BUG_SRBDS);
>
> - /*
> - * Processor MMIO Stale Data bug enumeration
> - *
> - * Affected CPU list is generally enough to enumerate the vulnerability,
> - * but for virtualization case check for ARCH_CAP MSR bits also, VMM may
> - * not want the guest to enumerate the bug.
> - */
> - if (cpu_matches(cpu_vuln_blacklist, MMIO) &&
> + /* Processor MMIO Stale Data bug enumeration */
> + if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
Why is that vendor check here? We have the cpu_vuln_blacklist for a
reason.
> !arch_cap_mmio_immune(ia32_cap))
> setup_force_cpu_bug(X86_BUG_MMIO_STALE_DATA);
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
