[PATCH v2] x86/bugs: Add "unknown" reporting for MMIO Stale Data

Pawan Gupta
2022-08-03T21:41:45Z

Older Intel CPUs that are not in the affected processor list for MMIO
Stale Data vulnerabilities currently report "Not affected" in sysfs,
which may not be correct. Vulnerability status for these older CPUs is
unknown.

Add known-not-affected CPUs to the whitelist. Report "unknown"
mitigation status for CPUs that are not in blacklist, whitelist and also
don't enumerate MSR ARCH_CAPABILITIES bits that reflect hardware
immunity to MMIO Stale Data vulnerabilities.

Mitigation is not deployed when the status is unknown.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Suggested-by: Tony Luck <tony.luck@intel.com>
Fixes: 8d50cdf8b834 ("x86/speculation/mmio: Add sysfs reporting for Processor MMIO Stale Data")
Cc: stable@vger.kernel.org
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
---
v1->v2:
- Set X86_BUG_MMIO_UNKNOWN for older Intel CPUs. (Borislav)
- Reporting for these CPUs changed to "Unknown: No mitigations". (Dave)
- Added known-not-affected CPUs to the whitelist. (Tony)
- Moved Servicing definition from commit message to MMIO Documentation.
(Borislav, Dave)

v1: https://lore.kernel.org/lkml/a932c154772f2121794a5f2eded1a11013114711.1657846269.git.pawan.kumar.gupta@linux.intel.com/

.../hw-vuln/processor_mmio_stale_data.rst | 14 +++++++
arch/x86/include/asm/cpufeatures.h | 3 +-
arch/x86/kernel/cpu/bugs.c | 12 +++++-
arch/x86/kernel/cpu/common.c | 40 ++++++++++++-------
4 files changed, 52 insertions(+), 17 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..c98fd11907cc 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 +230,20 @@ The possible values in this file are:
* - 'Mitigation: Clear CPU buffers'
- The processor is vulnerable and the CPU buffer clearing mitigation is
enabled.
+ * - 'Unknown: No mitigations'
+ - The processor vulnerability status is unknown because it is
+ out of Servicing period. Mitigation is not attempted.
+
+Definitions:
+------------
+
+Servicing period: The process of providing functional and security updates to
+Intel processors or platforms, utilizing the Intel Platform Update (IPU)
+process or other similar mechanisms.
+
+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.

If the processor is vulnerable then the following information is appended to
the above information:
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index a77b915d36a8..3e117226000d 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -455,6 +455,7 @@
#define X86_BUG_ITLB_MULTIHIT X86_BUG(23) /* CPU may incur MCE during certain page attribute changes */
#define X86_BUG_SRBDS X86_BUG(24) /* CPU may leak RNG bits if not mitigated */
#define X86_BUG_MMIO_STALE_DATA X86_BUG(25) /* CPU is affected by Processor MMIO Stale Data vulnerabilities */
-#define X86_BUG_RETBLEED X86_BUG(26) /* CPU is affected by RETBleed */
+#define X86_BUG_MMIO_UNKNOWN X86_BUG(26) /* CPU is too old and its MMIO Stale Data status is unknown */
+#define X86_BUG_RETBLEED X86_BUG(27) /* CPU is affected by RETBleed */

#endif /* _ASM_X86_CPUFEATURES_H */
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 6761668100b9..fe3f7e762b80 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -433,7 +433,8 @@ static void __init mmio_select_mitigation(void)
u64 ia32_cap;

if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA) ||
- cpu_mitigations_off()) {
+ boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN) ||
+ cpu_mitigations_off()) {
mmio_mitigation = MMIO_MITIGATION_OFF;
return;
}
@@ -2248,6 +2249,9 @@ static ssize_t tsx_async_abort_show_state(char *buf)

static ssize_t mmio_stale_data_show_state(char *buf)
{
+ if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN))
+ return sysfs_emit(buf, "Unknown: No mitigations\n");
+
if (mmio_mitigation == MMIO_MITIGATION_OFF)
return sysfs_emit(buf, "%s\n", mmio_strings[mmio_mitigation]);

@@ -2379,6 +2383,7 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
return srbds_show_state(buf);

case X86_BUG_MMIO_STALE_DATA:
+ case X86_BUG_MMIO_UNKNOWN:
return mmio_stale_data_show_state(buf);

case X86_BUG_RETBLEED:
@@ -2438,7 +2443,10 @@ ssize_t cpu_show_srbds(struct device *dev, struct device_attribute *attr, char *

ssize_t cpu_show_mmio_stale_data(struct device *dev, struct device_attribute *attr, char *buf)
{
- return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_STALE_DATA);
+ if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN))
+ return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_UNKNOWN);
+ else
+ return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_STALE_DATA);
}

ssize_t cpu_show_retbleed(struct device *dev, struct device_attribute *attr, char *buf)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 736262a76a12..471dc79c262b 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1135,6 +1135,7 @@ static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
#define NO_SWAPGS BIT(6)
#define NO_ITLB_MULTIHIT BIT(7)
#define NO_SPECTRE_V2 BIT(8)
+#define NO_MMIO BIT(9)

#define VULNWL(vendor, family, model, whitelist) \
X86_MATCH_VENDOR_FAM_MODEL(vendor, family, model, whitelist)
@@ -1157,6 +1158,11 @@ static const __initconst struct x86_cpu_id cpu_vuln_whitelist[] = {
VULNWL(VORTEX, 6, X86_MODEL_ANY, NO_SPECULATION),

/* Intel Family 6 */
+ VULNWL_INTEL(TIGERLAKE, NO_MMIO),
+ VULNWL_INTEL(TIGERLAKE_L, NO_MMIO),
+ VULNWL_INTEL(ALDERLAKE, NO_MMIO),
+ VULNWL_INTEL(ALDERLAKE_L, NO_MMIO),
+
VULNWL_INTEL(ATOM_SALTWELL, NO_SPECULATION | NO_ITLB_MULTIHIT),
VULNWL_INTEL(ATOM_SALTWELL_TABLET, NO_SPECULATION | NO_ITLB_MULTIHIT),
VULNWL_INTEL(ATOM_SALTWELL_MID, NO_SPECULATION | NO_ITLB_MULTIHIT),
@@ -1175,9 +1181,9 @@ static const __initconst struct x86_cpu_id cpu_vuln_whitelist[] = {
VULNWL_INTEL(ATOM_AIRMONT_MID, NO_L1TF | MSBDS_ONLY | NO_SWAPGS | NO_ITLB_MULTIHIT),
VULNWL_INTEL(ATOM_AIRMONT_NP, NO_L1TF | NO_SWAPGS | NO_ITLB_MULTIHIT),

- VULNWL_INTEL(ATOM_GOLDMONT, NO_MDS | NO_L1TF | NO_SWAPGS | NO_ITLB_MULTIHIT),
- VULNWL_INTEL(ATOM_GOLDMONT_D, NO_MDS | NO_L1TF | NO_SWAPGS | NO_ITLB_MULTIHIT),
- VULNWL_INTEL(ATOM_GOLDMONT_PLUS, NO_MDS | NO_L1TF | NO_SWAPGS | NO_ITLB_MULTIHIT),
+ VULNWL_INTEL(ATOM_GOLDMONT, NO_MDS | NO_L1TF | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),
+ VULNWL_INTEL(ATOM_GOLDMONT_D, NO_MDS | NO_L1TF | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),
+ VULNWL_INTEL(ATOM_GOLDMONT_PLUS, NO_MDS | NO_L1TF | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),

/*
* Technically, swapgs isn't serializing on AMD (despite it previously
@@ -1190,18 +1196,18 @@ static const __initconst struct x86_cpu_id cpu_vuln_whitelist[] = {
VULNWL_INTEL(ATOM_TREMONT_D, NO_ITLB_MULTIHIT),

/* AMD Family 0xf - 0x12 */
- VULNWL_AMD(0x0f, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT),
- VULNWL_AMD(0x10, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT),
- VULNWL_AMD(0x11, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT),
- VULNWL_AMD(0x12, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT),
+ VULNWL_AMD(0x0f, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),
+ VULNWL_AMD(0x10, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),
+ VULNWL_AMD(0x11, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),
+ VULNWL_AMD(0x12, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),

/* FAMILY_ANY must be last, otherwise 0x0f - 0x12 matches won't work */
- VULNWL_AMD(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT),
- VULNWL_HYGON(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT),
+ VULNWL_AMD(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),
+ VULNWL_HYGON(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),

/* Zhaoxin Family 7 */
- VULNWL(CENTAUR, 7, X86_MODEL_ANY, NO_SPECTRE_V2 | NO_SWAPGS),
- VULNWL(ZHAOXIN, 7, X86_MODEL_ANY, NO_SPECTRE_V2 | NO_SWAPGS),
+ VULNWL(CENTAUR, 7, X86_MODEL_ANY, NO_SPECTRE_V2 | NO_SWAPGS | NO_MMIO),
+ VULNWL(ZHAOXIN, 7, X86_MODEL_ANY, NO_SPECTRE_V2 | NO_SWAPGS | NO_MMIO),
{}
};

@@ -1355,10 +1361,16 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
* 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.
+ *
+ * Set X86_BUG_MMIO_UNKNOWN for CPUs that are neither in the blacklist,
+ * nor in the whitelist and also don't enumerate MSR ARCH_CAP MMIO bits.
*/
- if (cpu_matches(cpu_vuln_blacklist, MMIO) &&
- !arch_cap_mmio_immune(ia32_cap))
- setup_force_cpu_bug(X86_BUG_MMIO_STALE_DATA);
+ if (!arch_cap_mmio_immune(ia32_cap)) {
+ if (cpu_matches(cpu_vuln_blacklist, MMIO))
+ setup_force_cpu_bug(X86_BUG_MMIO_STALE_DATA);
+ else if (!cpu_matches(cpu_vuln_whitelist, NO_MMIO))
+ setup_force_cpu_bug(X86_BUG_MMIO_UNKNOWN);
+ }

if (!cpu_has(c, X86_FEATURE_BTC_NO)) {
if (cpu_matches(cpu_vuln_blacklist, RETBLEED) || (ia32_cap & ARCH_CAP_RSBA))

base-commit: 3d7cb6b04c3f3115719235cc6866b10326de34cd
--
2.36.1