fix: another attempt to avoid sigpipe on grep (#519)

Take this opportunity to factorize all the greps in /proc/cpuinfo
into a helper that avoids using a pipe to entirely avoid SIGPIPE
on a possibly gigantic /proc/cpuinfo

DEVELOPMENT.md

@@ -186,7 +186,7 @@ if [ $ret = $READ_CPUID_RET_OK ]; then
     cap_ssbd='Intel SSBD'
 elif [ $ret = $READ_CPUID_RET_ERR ] && [ "$g_mode" = live ]; then
     # CPUID device unavailable (e.g. in a VM): fall back to /proc/cpuinfo
-    if grep ^flags "$g_procfs/cpuinfo" | grep -qw ssbd; then
+    if cpuinfo_has_flag ssbd; then
         cap_ssbd='Intel SSBD (cpuinfo)'
         ret=$READ_CPUID_RET_OK
     fi

dist/doc/UNSUPPORTED_CVE_LIST.md

@@ -331,6 +331,17 @@ Improper access control in an on-chip debug interface could allow a privileged a
 
 **Why out of scope:** Not a transient or speculative execution vulnerability — this is an access-control flaw in a hardware debug/test interface (CWE-1191), with no side-channel or speculative execution component, and it requires a privileged attacker. There is no Linux kernel sysfs entry, no CPUID flag, and no kernel-side mitigation: the fix is delivered as platform/PSP firmware and proven via remote attestation against AMD's Key Distribution Service (KDS), with several SKUs marked "no fix planned." None of this is detectable by this tool, which inspects OS-loadable microcode revisions, CPUID/MSR bits, kernel capabilities, and sysfs.
 
+## CVE-2026-46174 — AMD Zen 2 Op Cache Improper Resource Isolation
+
+- **Bulletin:** [AMD-SB-7052](https://www.amd.com/en/resources/product-security/bulletin/amd-sb-7052.html) (CPU OP Cache Corruption)
+- **Kernel fix:** [commit 1e23b30a80b1](https://github.com/torvalds/linux/commit/1e23b30a80b14e5764657401ee2cca030525ae8e) — `x86/CPU/AMD: Prevent improper isolation of shared resources in Zen2's op cache`
+- **Affected CPUs:** AMD Zen 2
+- **CVSS:** 8.8 (High)
+
+Resources in the Zen 2 micro-op (op) cache can be improperly shared, causing instruction corruption that may be leveraged to execute instructions at a higher privilege level (userspace-to-kernel escalation). The Linux fix sets a bug-fix bit (bit 33) in the AMD `BP_CFG` model-specific register (`0xc001102e`) via `msr_set_bit()` in `init_amd_zen2()`, and only on bare metal (skipped when `X86_FEATURE_HYPERVISOR` is set, as the mitigation is the host's responsibility for guests).
+
+**Why out of scope:** Not a transient or speculative execution vulnerability — this is an op-cache resource-isolation bug that causes *instruction corruption* (an integrity/correctness erratum), with no side-channel or speculative data-leak component, which places it outside the vulnerability class this tool detects. It is also undetectable by this tool's standard framework: the kernel deliberately adds no `/sys/devices/system/cpu/vulnerabilities/` entry, no `X86_BUG_*` flag (so nothing in `/proc/cpuinfo`), no dmesg message, and no kernel command-line parameter. The mitigation is an unconditional inline MSR bit-set with no greppable named symbol, so it leaves no handle for no-runtime (kernel image / `System.map`) detection. The only possible check would be a live read of `BP_CFG` bit 33, which requires root and the `msr` module, works on bare metal only (guests report `N/A`), and would be a bespoke one-off outside the established CVE-detection model — the same situation as the [JCC Erratum](#no-cve--jump-conditional-code-jcc-erratum) below, but for AMD.
+
 ## No CVE — Jump Conditional Code (JCC) Erratum
 
 - **Issue:** [#329](https://github.com/speed47/spectre-meltdown-checker/issues/329)

src/libs/210_cpu_detect.sh

@@ -195,6 +195,14 @@ is_arch_cap_mmio_immune() {
     [ "$cap_sbdr_ssdp_no" = 1 ] && [ "$cap_fbsdp_no" = 1 ] && [ "$cap_psdp_no" = 1 ]
 }
 
+# Whether the MMIO arch-cap immunity bits are undetermined because the
+# IA32_ARCH_CAPABILITIES MSR couldn't be read (msr module unavailable or kernel
+# lockdown).
+# Returns: 0 if undetermined, 1 otherwise
+is_arch_cap_mmio_undetermined() {
+    [ "$cap_sbdr_ssdp_no" = -1 ] || [ "$cap_fbsdp_no" = -1 ] || [ "$cap_psdp_no" = -1 ]
+}
+
 # Check whether the CPU is known to be unaffected by MMIO Stale Data (CVE-2022-21123/21125/21166)
 # Matches the kernel's NO_MMIO whitelist plus arch_cap_mmio_immune().
 # Model inventory and kernel-commit history are documented in check_mmio_linux().

src/libs/330_cpu_misc.sh

@@ -9,7 +9,7 @@ dmesg_grep() {
         # dmesg truncated
         return 2
     fi
-    ret_dmesg_grep_grepped=$(dmesg 2>/dev/null | grep -E "$1" | head -n1)
+    ret_dmesg_grep_grepped=$(dmesg 2>/dev/null | grep -m 1 -E "$1")
     # not found:
     [ -z "$ret_dmesg_grep_grepped" ] && return 1
     # found, output is in $ret_dmesg_grep_grepped
@@ -22,3 +22,9 @@ is_coreos() {
     command -v coreos-install >/dev/null 2>&1 && command -v toolbox >/dev/null 2>&1 && return 0
     return 1
 }
+
+# Check whether /proc/cpuinfo has $1 in the flags line
+# Returns: 0 if flag found, 1 otherwise
+cpuinfo_has_flag() {
+    grep -Eq '^flags\b.+\b'"$1"'\b' "$g_procfs/cpuinfo" 2>/dev/null
+}

src/libs/350_cpu_detect2.sh

@@ -20,8 +20,8 @@ parse_cpu_details() {
     cap_avx2=0
     cap_avx512=0
     if [ -e "$g_procfs/cpuinfo" ]; then
-        if grep -qw avx2 "$g_procfs/cpuinfo" 2>/dev/null; then cap_avx2=1; fi
+        if cpuinfo_has_flag avx2; then cap_avx2=1; fi
-        if grep -qw avx512 "$g_procfs/cpuinfo" 2>/dev/null; then cap_avx512=1; fi
+        if cpuinfo_has_flag avx512; then cap_avx512=1; fi
         cpu_vendor=$(grep '^vendor_id' "$g_procfs/cpuinfo" | awk '{print $3}' | head -n1)
         cpu_friendly_name=$(grep '^model name' "$g_procfs/cpuinfo" | cut -d: -f2- | head -n1 | sed -e 's/^ *//')
         # ARM-style cpuinfo: parse per-core implementer/part/arch/variant/revision lists

src/libs/370_hw_vmm.sh

@@ -1,25 +1,41 @@
 # vim: set ts=4 sw=4 sts=4 et:
-# Check whether the system is running as a Xen paravirtualized guest
+
-# Returns: 0 if Xen PV, 1 otherwise
+# Probe Xen presence and guest type using the most reliable sources available.
-is_xen() {
+# Prefer /sys/hypervisor when avalable, fallback to dmesg otherwise.
-    local ret
+# Caches results in g_xen (1/0) and g_xen_guest_type (PV|PVH|HVM|'').
-    if [ ! -d "$g_procfs/xen" ]; then
+_detect_xen() {
-        return 1
+    [ "${g_xen_cached:-0}" = 1 ] && return
+    g_xen=0
+    g_xen_guest_type=''
+    g_xen_cached=1
+
+    # Most reliable: /sys/hypervisor/type is 'xen' on any Xen domain (dom0
+    # included), and /sys/hypervisor/guest_type reports PV, PVH or HVM.
+    if [ -r /sys/hypervisor/type ] && [ "$(cat /sys/hypervisor/type 2>/dev/null)" = xen ]; then
+        g_xen=1
+        if [ -r /sys/hypervisor/guest_type ]; then
+            g_xen_guest_type=$(cat /sys/hypervisor/guest_type 2>/dev/null)
+        fi
+        return
     fi
 
-    # XXX do we have a better way that relying on dmesg?
+    # Fallback for kernels without /sys/hypervisor: /proc/xen plus a dmesg probe.
-    dmesg_grep 'Booting paravirtualized kernel on Xen$'
+    if [ -d "$g_procfs/xen" ]; then
-    ret=$?
+        dmesg_grep 'Booting paravirtualized kernel on Xen$'
-    if [ "$ret" -eq 2 ]; then
+        case $? in
-        pr_warn "dmesg truncated, Xen detection will be unreliable. Please reboot and relaunch this script"
+            0) g_xen=1 ;;
-        return 1
+            2) pr_warn "dmesg truncated, Xen detection will be unreliable. Please reboot and relaunch this script" ;;
-    elif [ "$ret" -eq 0 ]; then
+        esac
-        return 0
-    else
-        return 1
     fi
 }
 
+# Check whether the system is running on Xen (any domain type, dom0 included).
+# Returns: 0 if Xen, 1 otherwise
+is_xen() {
+    _detect_xen
+    [ "$g_xen" = 1 ]
+}
+
 # Check whether the system is a Xen Dom0 (privileged domain)
 # Returns: 0 if Dom0, 1 otherwise
 is_xen_dom0() {
@@ -34,31 +50,77 @@ is_xen_dom0() {
     fi
 }
 
-# Check whether the system is a Xen DomU (unprivileged PV guest)
+# Check whether the system is running as a Xen PV DomU (the only Xen guest type
-# Returns: 0 if DomU, 1 otherwise
+# affected by Meltdown, which needs Xen-level mitigation).
+# Returns: 0 if PV DomU, 1 otherwise
 is_xen_domU() {
     local ret
     if ! is_xen; then
         return 1
     fi
 
-    # PVHVM guests also print 'Booting paravirtualized kernel', so we need this check.
+    if is_xen_dom0; then
+        return 1
+    fi
+
+    # When the reliable guest type is known, only PV domains (which aren't
+    # dom0, checked above) are the PV DomU case. PVH and HVM guests are not.
+    if [ -n "$g_xen_guest_type" ]; then
+        [ "$g_xen_guest_type" = PV ] && return 0
+        return 1
+    fi
+
+    # Fallback (no /sys/hypervisor/guest_type): PVHVM guests also print the
+    # 'Booting paravirtualized kernel' line, so exclude them via dmesg.
     dmesg_grep 'Xen HVM callback vector for event delivery is enabled$'
     ret=$?
     if [ "$ret" -eq 0 ]; then
         return 1
     fi
 
-    if ! is_xen_dom0; then
+    return 0
-        return 0
-    else
-        return 1
-    fi
 }
 
-# Check whether the system is running as a guest inside a virtual machine.
+# Check whether we're running inside an OS-level container (LXC, Docker,
+# systemd-nspawn, etc.). Containers share the host kernel, so host/hypervisor
+# introspection (e.g. telling a Xen dom0 from a domU) is unreliable from inside
+# one: /proc/xen is exposed but empty, dmesg is the host's, etc. (issue #173)
+# Returns: 0 if in a container, 1 otherwise
+# Sets: g_is_container (1/0), g_container_reason
+is_running_in_container() {
+    local ctype
+    if [ "${g_is_container_cached:-0}" != 1 ]; then
+        g_is_container=0
+        g_container_reason=''
+        # systemd and most runtimes export 'container=' to PID 1's environment
+        if [ -r "$g_procfs/1/environ" ]; then
+            ctype=$(tr '\0' '\n' <"$g_procfs/1/environ" 2>/dev/null | sed -n 's/^container=//p' | head -n1)
+            if [ -n "$ctype" ]; then
+                g_is_container=1
+                g_container_reason="container=$ctype in $g_procfs/1/environ"
+            fi
+        fi
+        # Docker (and some others) drop a marker file at the filesystem root
+        if [ "$g_is_container" = 0 ] && [ -e /.dockerenv ]; then
+            g_is_container=1
+            g_container_reason="/.dockerenv present"
+        fi
+        # cgroup membership often reveals the runtime (lxc, docker, kubepods, ...)
+        if [ "$g_is_container" = 0 ] && [ -r "$g_procfs/1/cgroup" ]; then
+            if grep -qE '(^|[:/])(lxc|docker|kubepods|libpod|containerd|machine\.slice)([/.]|$)' "$g_procfs/1/cgroup" 2>/dev/null; then
+                g_is_container=1
+                g_container_reason="container runtime found in $g_procfs/1/cgroup"
+            fi
+        fi
+        g_is_container_cached=1
+    fi
+    [ "$g_is_container" = 1 ]
+}
+
+# Check whether the system is running as a guest inside a VM.
 # Uses the 'hypervisor' CPUID feature flag exposed in /proc/cpuinfo by KVM,
 # VMware, Hyper-V, VirtualBox, and most other type-1 and type-2 hypervisors.
+# Xen PV/PVH DomUs don't set that flag, so they're detected separately.
 # Returns: 0 if running as a VM guest, 1 otherwise
 # Sets: g_is_guest_vm (1=guest, 0=not a guest), g_is_guest_vm_reason
 is_running_as_guest() {
@@ -69,6 +131,13 @@ is_running_as_guest() {
             g_is_guest_vm=1
             g_is_guest_vm_reason="'hypervisor' flag in $g_procfs/cpuinfo"
         fi
+        # Xen PV/PVH DomUs don't expose the 'hypervisor' CPUID flag. Don't
+        # classify a container on a Xen host as a guest here: we can't tell
+        # dom0 from domU from inside a container (handled separately).
+        if [ "$g_is_guest_vm" = 0 ] && is_xen && ! is_xen_dom0 && ! is_running_in_container; then
+            g_is_guest_vm=1
+            g_is_guest_vm_reason="Xen ${g_xen_guest_type:-PV} DomU"
+        fi
         g_is_guest_vm_cached=1
     fi
     [ "$g_is_guest_vm" = 1 ]

src/libs/400_hw_check.sh

@@ -415,6 +415,22 @@ check_cpu() {
                 pstatus green NO
             fi
         fi
+        # ARM exposes no userspace-readable CPUID/MSR to query SSBD support directly.
+        # The ARMv8.5 SSBS ("Speculative Store Bypass Safe") hardware bit, when present,
+        # surfaces as the 'ssbs' hwcap in /proc/cpuinfo. We use it *only* as a positive
+        # confirmation of SSB mitigation capability (Variant 4 / CVE-2018-3639): its
+        # absence proves nothing, because the kernel deliberately hides the hwcap on some
+        # cores (e.g. the erratum-3194386 SSBS self-sync workaround), so we must never
+        # infer immunity from a missing 'ssbs'.
+        if has_runtime; then
+            pr_info_nol "  * CPU indicates SSBS (Speculative Store Bypass Safe) capability: "
+            if grep '^Features' "$g_procfs/cpuinfo" | grep -qw ssbs; then
+                cap_ssbd='ARM SSBS (cpuinfo)'
+                pstatus green YES "$cap_ssbd"
+            else
+                pstatus blue UNKNOWN "not exposed (the kernel may hide it; cannot conclude)"
+            fi
+        fi
         return
     fi
 
@@ -497,7 +513,7 @@ check_cpu() {
     fi
     if [ -z "$cap_ibrs" ] && [ $ret = $READ_CPUID_RET_ERR ] && has_runtime; then
         # CPUID device unavailable (e.g. in a VM): fall back to /proc/cpuinfo
-        if grep ^flags "$g_procfs/cpuinfo" | grep -qw ibrs; then
+        if cpuinfo_has_flag ibrs; then
             cap_ibrs='IBRS (cpuinfo)'
             cap_spec_ctrl=1
             pstatus green YES "ibrs flag in $g_procfs/cpuinfo"
@@ -572,7 +588,7 @@ check_cpu() {
         if [ $ret = $READ_CPUID_RET_OK ]; then
             cap_ibpb='IBPB_SUPPORT'
             pstatus green YES "IBPB_SUPPORT feature bit"
-        elif [ $ret = $READ_CPUID_RET_ERR ] && has_runtime && grep ^flags "$g_procfs/cpuinfo" | grep -qw ibpb; then
+        elif [ $ret = $READ_CPUID_RET_ERR ] && has_runtime && cpuinfo_has_flag ibpb; then
             # CPUID device unavailable (e.g. in a VM): fall back to /proc/cpuinfo
             cap_ibpb='IBPB (cpuinfo)'
             pstatus green YES "ibpb flag in $g_procfs/cpuinfo"
@@ -645,7 +661,7 @@ check_cpu() {
     fi
     if [ -z "$cap_stibp" ] && [ $ret = $READ_CPUID_RET_ERR ] && has_runtime; then
         # CPUID device unavailable (e.g. in a VM): fall back to /proc/cpuinfo
-        if grep ^flags "$g_procfs/cpuinfo" | grep -qw stibp; then
+        if cpuinfo_has_flag stibp; then
             cap_stibp='STIBP (cpuinfo)'
             pstatus green YES "stibp flag in $g_procfs/cpuinfo"
             ret=$READ_CPUID_RET_OK
@@ -717,9 +733,9 @@ check_cpu() {
 
     if [ -z "$cap_ssbd" ] && [ "$ret24" = $READ_CPUID_RET_ERR ] && [ "$ret25" = $READ_CPUID_RET_ERR ] && has_runtime; then
         # CPUID device unavailable (e.g. in a VM): fall back to /proc/cpuinfo
-        if grep ^flags "$g_procfs/cpuinfo" | grep -qw ssbd; then
+        if cpuinfo_has_flag ssbd; then
             cap_ssbd='SSBD (cpuinfo)'
-        elif grep ^flags "$g_procfs/cpuinfo" | grep -qw virt_ssbd; then
+        elif cpuinfo_has_flag virt_ssbd; then
             cap_ssbd='SSBD in VIRT_SPEC_CTRL (cpuinfo)'
         fi
     fi
@@ -779,7 +795,7 @@ check_cpu() {
     if [ $ret = $READ_CPUID_RET_OK ]; then
         pstatus green YES "L1D flush feature bit"
         cap_l1df=1
-    elif [ $ret = $READ_CPUID_RET_ERR ] && has_runtime && grep ^flags "$g_procfs/cpuinfo" | grep -qw flush_l1d; then
+    elif [ $ret = $READ_CPUID_RET_ERR ] && has_runtime && cpuinfo_has_flag flush_l1d; then
         # CPUID device unavailable (e.g. in a VM): fall back to /proc/cpuinfo
         pstatus green YES "flush_l1d flag in $g_procfs/cpuinfo"
         cap_l1df=1
@@ -799,7 +815,7 @@ check_cpu() {
         if [ $ret = $READ_CPUID_RET_OK ]; then
             cap_md_clear=1
             pstatus green YES "MD_CLEAR feature bit"
-        elif [ $ret = $READ_CPUID_RET_ERR ] && has_runtime && grep ^flags "$g_procfs/cpuinfo" | grep -qw md_clear; then
+        elif [ $ret = $READ_CPUID_RET_ERR ] && has_runtime && cpuinfo_has_flag md_clear; then
             # CPUID device unavailable (e.g. in a VM): fall back to /proc/cpuinfo
             cap_md_clear=1
             pstatus green YES "md_clear flag in $g_procfs/cpuinfo"
@@ -869,7 +885,7 @@ check_cpu() {
         if [ $ret = $READ_CPUID_RET_OK ]; then
             pstatus green YES
             cap_arch_capabilities=1
-        elif [ $ret = $READ_CPUID_RET_ERR ] && has_runtime && grep ^flags "$g_procfs/cpuinfo" | grep -qw arch_capabilities; then
+        elif [ $ret = $READ_CPUID_RET_ERR ] && has_runtime && cpuinfo_has_flag arch_capabilities; then
             # CPUID device unavailable (e.g. in a VM): fall back to /proc/cpuinfo
             pstatus green YES "arch_capabilities flag in $g_procfs/cpuinfo"
             cap_arch_capabilities=1
@@ -971,8 +987,33 @@ check_cpu() {
                     pstatus yellow NO
                 fi
             elif [ $ret = $READ_MSR_RET_KO ]; then
+                # the MSR access faulted: the register is genuinely absent, so the
+                # pre-seeded 0 ("not advertised") values are correct.
                 pstatus yellow NO
             else
+                # RET_ERR (no msr module) or RET_LOCKDOWN (MSR reads restricted):
+                # CPUID told us the MSR exists but we couldn't read it, so its bits
+                # are undetermined, not 0. Leaving them at 0 would falsely claim the
+                # CPU "explicitly indicates not immune".
+                # Reset every arch-cap-derived value to -1 (UNKNOWN) instead.
+                cap_rdcl_no=-1
+                cap_taa_no=-1
+                cap_mds_no=-1
+                cap_ibrs_all=-1
+                cap_rsba=-1
+                cap_l1dflush_no=-1
+                cap_ssb_no=-1
+                cap_pschange_msc_no=-1
+                cap_tsx_ctrl_msr=-1
+                cap_gds_ctrl=-1
+                cap_gds_no=-1
+                cap_rfds_no=-1
+                cap_rfds_clear=-1
+                cap_its_no=-1
+                cap_sbdr_ssdp_no=-1
+                cap_fbsdp_no=-1
+                cap_psdp_no=-1
+                cap_fb_clear=-1
                 pstatus yellow UNKNOWN "$ret_read_msr_msg"
             fi
         fi

src/vulns-helpers/check_mds.sh

@@ -138,7 +138,7 @@ check_mds_linux() {
         if is_x86_kernel; then
             pr_info_nol "* Kernel supports using MD_CLEAR mitigation: "
             kernel_md_clear_can_tell=1
-            if [ "$g_mode" = live ] && grep ^flags "$g_procfs/cpuinfo" | grep -qw md_clear; then
+            if [ "$g_mode" = live ] && cpuinfo_has_flag md_clear; then
                 kernel_md_clear="md_clear found in $g_procfs/cpuinfo"
                 pstatus green YES "$kernel_md_clear"
             fi
@@ -174,6 +174,12 @@ check_mds_linux() {
                 if echo "$ret_sys_interface_check_fullmsg" | grep -Eq 'SMT (disabled|mitigated)'; then
                     mds_smt_mitigated=1
                     pstatus green YES
+                elif echo "$ret_sys_interface_check_fullmsg" | grep -q 'SMT Host state unknown'; then
+                    # The kernel appends "SMT Host state unknown" when running under
+                    # a hypervisor (X86_FEATURE_HYPERVISOR): the host controls SMT
+                    # scheduling, so it can't be determined from inside the guest (#343).
+                    mds_smt_mitigated=2
+                    pstatus yellow UNKNOWN "running in a VM guest, the hypervisor host controls SMT"
                 else
                     mds_smt_mitigated=0
                     pstatus yellow NO
@@ -200,6 +206,9 @@ check_mds_linux() {
                             if [ "$opt_paranoid" != 1 ] || [ "$mds_smt_mitigated" = 1 ]; then
                                 mystatus=OK
                                 mymsg="Your microcode and kernel are both up to date for this mitigation, and mitigation is enabled"
+                            elif [ "$mds_smt_mitigated" = 2 ]; then
+                                mystatus=UNK
+                                mymsg="Your microcode and kernel are both up to date for this mitigation and it's enabled, but SMT (Hyper-Threading) cross-thread protection can't be verified from inside a VM guest: it depends on the hypervisor host's SMT/core-scheduling configuration"
                             else
                                 mystatus=VULN
                                 mymsg="Your microcode and kernel are both up to date for this mitigation, but you must disable SMT (Hyper-Threading) for a complete mitigation"

src/vulns-helpers/check_mmio.sh

@@ -6,15 +6,22 @@ check_mmio_bsd() {
     # the only partial defense available, and without OS-level VERW invocation it
     # cannot close the vulnerability.
     local unk
-    unk="your CPU's MMIO Stale Data status is unknown (Intel never officially assessed this CPU, its servicing period has ended)"
     if ! is_cpu_affected "$cve"; then
         pvulnstatus "$cve" OK "your CPU vendor reported your CPU model as not affected"
     elif is_cpu_mmio_unknown; then
-        if [ "$opt_paranoid" = 1 ]; then
+        if is_arch_cap_mmio_undetermined; then
-            pvulnstatus "$cve" VULN "$unk, and no BSD mitigation exists"
+            # We only landed in the "unknown" bucket because the IA32_ARCH_CAPABILITIES
-            explain "There is no known mitigation for this CPU model. Even with up-to-date microcode, BSD kernels do not invoke VERW for MMIO Stale Data clearing. Only a hardware replacement can fully address this."
+            # MSR couldn't be read: the CPU might actually advertise MMIO immunity.
+            unk="your CPU's MMIO Stale Data status could not be determined: the IA32_ARCH_CAPABILITIES MSR (0x10a) couldn't be read"
+            pvulnstatus "$cve" UNK "$unk; load the cpuctl module and/or re-run as root to get a definitive answer"
         else
-            pvulnstatus "$cve" UNK "$unk; no BSD mitigation exists in any case"
+            unk="your CPU's MMIO Stale Data status is unknown (Intel never officially assessed this CPU, its servicing period has ended)"
+            if [ "$opt_paranoid" = 1 ]; then
+                pvulnstatus "$cve" VULN "$unk, and no BSD mitigation exists"
+                explain "There is no known mitigation for this CPU model. Even with up-to-date microcode, BSD kernels do not invoke VERW for MMIO Stale Data clearing. Only a hardware replacement can fully address this."
+            else
+                pvulnstatus "$cve" UNK "$unk; no BSD mitigation exists in any case"
+            fi
         fi
     else
         pvulnstatus "$cve" VULN "your CPU is affected and no BSD has implemented an MMIO Stale Data mitigation"
@@ -24,7 +31,7 @@ check_mmio_bsd() {
 
 # MMIO Stale Data (Processor MMIO Stale Data Vulnerabilities) - Linux mitigation check
 check_mmio_linux() {
-    local status sys_interface_available msg kernel_mmio kernel_mmio_can_tell mmio_mitigated mmio_smt_mitigated mystatus mymsg unk
+    local status sys_interface_available msg kernel_mmio kernel_mmio_can_tell kernel_mmio_unknown_aware mmio_mitigated mmio_smt_mitigated mystatus mymsg unk
     status=UNK
     sys_interface_available=0
     msg=''
@@ -166,6 +173,11 @@ check_mmio_linux() {
         # MMIO Stale Data is Intel-only; skip x86-specific kernel/MSR checks on non-x86 kernels
         kernel_mmio=''
         kernel_mmio_can_tell=0
+        # Whether this kernel implements the X86_BUG_MMIO_UNKNOWN distinction, i.e. can
+        # report "Unknown: No mitigations" for CPUs Intel never assessed. Only such kernels
+        # emit a *trustworthy* "Not affected": they would have said "Unknown" instead if the
+        # CPU were in the unknown bucket. Detected by the presence of the literal sysfs string in the kernel image.
+        kernel_mmio_unknown_aware=0
         if is_x86_kernel; then
             pr_info_nol "* Kernel supports MMIO Stale Data mitigation: "
             kernel_mmio_can_tell=1
@@ -176,6 +188,10 @@ check_mmio_linux() {
                 kernel_mmio='found MMIO Stale Data mitigation evidence in kernel image'
                 pstatus green YES "$kernel_mmio"
             fi
+            if [ -z "$g_kernel_err" ] && grep -qF 'Unknown: No mitigations' "$g_kernel" 2>/dev/null; then
+                pr_debug "mmio: kernel image knows the 'Unknown: No mitigations' state (X86_BUG_MMIO_UNKNOWN-aware)"
+                kernel_mmio_unknown_aware=1
+            fi
             if [ -z "$kernel_mmio" ] && [ -n "$opt_config" ] && grep -q '^CONFIG_MITIGATION_MMIO_STALE_DATA=y' "$opt_config"; then
                 kernel_mmio='found MMIO Stale Data mitigation config option enabled'
                 pstatus green YES "$kernel_mmio"
@@ -216,6 +232,12 @@ check_mmio_linux() {
                 if echo "$ret_sys_interface_check_fullmsg" | grep -Eq 'SMT (disabled|mitigated)'; then
                     mmio_smt_mitigated=1
                     pstatus green YES
+                elif echo "$ret_sys_interface_check_fullmsg" | grep -q 'SMT Host state unknown'; then
+                    # The kernel appends "SMT Host state unknown" when running under
+                    # a hypervisor (X86_FEATURE_HYPERVISOR): the host controls SMT
+                    # scheduling, so it can't be determined from inside the guest (#343).
+                    mmio_smt_mitigated=2
+                    pstatus yellow UNKNOWN "running in a VM guest, the hypervisor host controls SMT"
                 else
                     mmio_smt_mitigated=0
                     pstatus yellow NO
@@ -235,12 +257,32 @@ check_mmio_linux() {
         # Bypass the normal sysfs reconciliation: sysfs reports "Unknown: No mitigations"
         # only on v6.0-v6.15. On earlier and on v6.16+ kernels it wrongly says "Not affected"
         # for these CPUs (which predate FB_CLEAR microcode and Intel's affected-processor list).
-        unk="your CPU's MMIO Stale Data status is unknown (Intel never officially assessed this CPU, its servicing period has ended)"
+        if is_arch_cap_mmio_undetermined; then
-        if [ "$opt_paranoid" = 1 ]; then
+            # We landed in the "unknown" bucket only because the IA32_ARCH_CAPABILITIES
-            pvulnstatus "$cve" VULN "$unk, and no mitigation is available"
+            # MSR couldn't be read from userspace (no msr module, or kernel lockdown under
-            explain "There is no known mitigation for this CPU model. Intel ended its servicing period without evaluating whether it is affected by MMIO Stale Data vulnerabilities, so no FB_CLEAR-capable microcode was released. Consider replacing affected hardware."
+            # Secure Boot): the CPU might actually advertise MMIO immunity
+            # through FBSDP_NO/PSDP_NO/SBDR_SSDP_NO, but we can't read it, however the kernel can.
+            #
+            # We can trust a sysfs "Not affected" only if this kernel is X86_BUG_MMIO_UNKNOWN-aware:
+            # such a kernel would have reported "Unknown: No mitigations" instead if the CPU were in
+            # the unknown bucket, so "Not affected" genuinely means arch-cap immune.
+            # On kernels that lack that distinction, a "Not affected" is not trustworthy for these CPUs,
+            # so we keep UNK.
+            if [ "$g_mode" = live ] && [ "$sys_interface_available" = 1 ] &&
+                [ "$kernel_mmio_unknown_aware" = 1 ] && [ "$status" = OK ]; then
+                pvulnstatus "$cve" OK "your kernel reports your CPU as not affected, and this kernel distinguishes the MMIO 'unknown' state, so its verdict is trustworthy (we couldn't read the IA32_ARCH_CAPABILITIES MSR ourselves)"
+            else
+                unk="your CPU's MMIO Stale Data status could not be determined: the IA32_ARCH_CAPABILITIES MSR (0x10a) couldn't be read"
+                pvulnstatus "$cve" UNK "$unk; load the msr module and/or disable kernel lockdown, then re-run as root to get a definitive answer"
+            fi
         else
-            pvulnstatus "$cve" UNK "$unk; no mitigation is available in any case"
+            unk="your CPU's MMIO Stale Data status is unknown (Intel never officially assessed this CPU, its servicing period has ended)"
+            if [ "$opt_paranoid" = 1 ]; then
+                pvulnstatus "$cve" VULN "$unk, and no mitigation is available"
+                explain "There is no known mitigation for this CPU model. Intel ended its servicing period without evaluating whether it is affected by MMIO Stale Data vulnerabilities, so no FB_CLEAR-capable microcode was released."
+            else
+                pvulnstatus "$cve" UNK "$unk; no mitigation is available in any case"
+            fi
         fi
     else
         if [ "$opt_sysfs_only" != 1 ]; then
@@ -253,6 +295,9 @@ check_mmio_linux() {
                             if [ "$opt_paranoid" != 1 ] || [ "$mmio_smt_mitigated" = 1 ]; then
                                 mystatus=OK
                                 mymsg="Your microcode and kernel are both up to date for this mitigation, and mitigation is enabled"
+                            elif [ "$mmio_smt_mitigated" = 2 ]; then
+                                mystatus=UNK
+                                mymsg="Your microcode and kernel are both up to date for this mitigation and it's enabled, but SMT (Hyper-Threading) cross-thread protection can't be verified from inside a VM guest: it depends on the hypervisor host's SMT/core-scheduling configuration"
                             else
                                 mystatus=VULN
                                 mymsg="Your microcode and kernel are both up to date for this mitigation, but you must disable SMT (Hyper-Threading) for a complete mitigation"

src/vulns/CVE-2017-5715.sh

@@ -306,7 +306,7 @@ check_CVE_2017_5715_linux() {
                 # which in that case means ibrs is supported *and* enabled for kernel & user
                 # as per the ibrs patch series v3
                 if [ -z "$g_ibrs_supported" ]; then
-                    if grep ^flags "$g_procfs/cpuinfo" | grep -qw spec_ctrl_ibrs; then
+                    if cpuinfo_has_flag spec_ctrl_ibrs; then
                         pr_debug "ibrs: found spec_ctrl_ibrs flag in $g_procfs/cpuinfo"
                         g_ibrs_supported="spec_ctrl_ibrs flag in $g_procfs/cpuinfo"
                         # enabled=2 -> kernel & user

src/vulns/CVE-2017-5754.sh

@@ -11,7 +11,7 @@
 pti_performance_check() {
     local ret pcid invpcid
     pr_info_nol "  * Reduced performance impact of PTI: "
-    if [ -e "$g_procfs/cpuinfo" ] && grep ^flags "$g_procfs/cpuinfo" | grep -qw pcid; then
+    if cpuinfo_has_flag pcid; then
         pcid=1
     else
         read_cpuid 0x1 0x0 "$ECX" 17 1 1
@@ -21,7 +21,7 @@ pti_performance_check() {
         fi
     fi
 
-    if [ -e "$g_procfs/cpuinfo" ] && grep ^flags "$g_procfs/cpuinfo" | grep -qw invpcid; then
+    if cpuinfo_has_flag invpcid; then
         invpcid=1
     else
         read_cpuid 0x7 0x0 "$EBX" 10 1 1
@@ -45,7 +45,7 @@ check_CVE_2017_5754() {
 }
 
 check_CVE_2017_5754_linux() {
-    local status sys_interface_available msg kpti_support kpti_can_tell kpti_enabled dmesg_grep pti_xen_pv_domU xen_pv_domo xen_pv_domu explain_text
+    local status sys_interface_available msg kpti_support kpti_can_tell kpti_enabled dmesg_grep pti_xen_pv_domU xen_pv_domo xen_pv_domu xen_unknown_container explain_text
     status=UNK
     sys_interface_available=0
     msg=''
@@ -110,11 +110,11 @@ check_CVE_2017_5754_linux() {
             dmesg_grep="$dmesg_grep|x86/pti: Unmapping kernel while in userspace"
             # aarch64
             dmesg_grep="$dmesg_grep|CPU features: detected( feature)?: Kernel page table isolation \(KPTI\)"
-            if grep ^flags "$g_procfs/cpuinfo" | grep -qw pti; then
+            if cpuinfo_has_flag pti; then
                 # vanilla PTI patch sets the 'pti' flag in cpuinfo
                 pr_debug "kpti_enabled: found 'pti' flag in $g_procfs/cpuinfo"
                 kpti_enabled=1
-            elif grep ^flags "$g_procfs/cpuinfo" | grep -qw kaiser; then
+            elif cpuinfo_has_flag kaiser; then
                 # kernel line 4.9 sets the 'kaiser' flag in cpuinfo
                 pr_debug "kpti_enabled: found 'kaiser' flag in $g_procfs/cpuinfo"
                 kpti_enabled=1
@@ -167,14 +167,24 @@ check_CVE_2017_5754_linux() {
     # Test if the current host is a Xen PV Dom0 / DomU
     xen_pv_domo=0
     xen_pv_domu=0
-    is_xen_dom0 && xen_pv_domo=1
+    xen_unknown_container=0
-    is_xen_domU && xen_pv_domu=1
+    if is_xen && ! is_xen_dom0 && is_running_in_container; then
+        # We can see Xen, but we're inside a container so /proc/xen/capabilities
+        # isn't exposed and dmesg is the host's: we can't tell a safe Dom0 from
+        # a vulnerable PV DomU from in here (issue #173).
+        xen_unknown_container=1
+    else
+        is_xen_dom0 && xen_pv_domo=1
+        is_xen_domU && xen_pv_domu=1
+    fi
 
     if [ "$g_mode" = live ]; then
         # checking whether we're running under Xen PV 64 bits. If yes, we are affected by affected_variant3
         # (unless we are a Dom0)
         pr_info_nol "* Running as a Xen PV DomU: "
-        if [ "$xen_pv_domu" = 1 ]; then
+        if [ "$xen_unknown_container" = 1 ]; then
+            pstatus yellow UNKNOWN "running in a container, can't query Xen from here"
+        elif [ "$xen_pv_domu" = 1 ]; then
             pstatus yellow YES
         else
             pstatus blue NO
@@ -187,7 +197,10 @@ check_CVE_2017_5754_linux() {
     elif [ -z "$msg" ]; then
         # if msg is empty, sysfs check didn't fill it, rely on our own test
         if [ "$g_mode" = live ]; then
-            if [ "$kpti_enabled" = 1 ]; then
+            if [ "$xen_unknown_container" = 1 ]; then
+                pvulnstatus "$cve" UNK "running inside a container on a Xen host, can't determine if the underlying domain is a vulnerable PV DomU"
+                explain "This system looks like a container ($g_container_reason) running on a Xen host. Whether the underlying domain is a safe Dom0 or a vulnerable PV DomU can't be reliably determined from inside a container (/proc/xen is exposed but empty, and dmesg belongs to the host). Please re-run this script directly on the host, outside the container, to get an accurate result."
+            elif [ "$kpti_enabled" = 1 ]; then
                 pvulnstatus "$cve" OK "PTI mitigates the vulnerability"
             elif [ "$xen_pv_domo" = 1 ]; then
                 pvulnstatus "$cve" OK "Xen Dom0s are safe and do not require PTI"

src/vulns/CVE-2018-3646.sh

@@ -89,7 +89,7 @@ check_CVE_2018_3646_linux() {
 
         pr_info "* Mitigation 2"
         pr_info_nol "  * L1D flush is supported by kernel: "
-        if [ "$g_mode" = live ] && grep -qw flush_l1d "$g_procfs/cpuinfo"; then
+        if [ "$g_mode" = live ] && cpuinfo_has_flag flush_l1d; then
             l1d_kernel="found flush_l1d in $g_procfs/cpuinfo"
         fi
         if [ -z "$l1d_kernel" ]; then
@@ -162,7 +162,7 @@ check_CVE_2018_3646_linux() {
 
         pr_info_nol "  * Hardware-backed L1D flush supported: "
         if [ "$g_mode" = live ]; then
-            if grep -qw flush_l1d "$g_procfs/cpuinfo" || [ -n "$l1d_xen_hardware" ]; then
+            if cpuinfo_has_flag flush_l1d || [ -n "$l1d_xen_hardware" ]; then
                 pstatus green YES "performance impact of the mitigation will be greatly reduced"
             else
                 pstatus blue NO "flush will be done in software, this is slower"

src/vulns/CVE-2019-11135.sh

@@ -86,6 +86,11 @@ check_CVE_2019_11135_linux() {
                 pvulnstatus "$cve" VULN "TSX must be disabled for full mitigation"
             elif echo "$ret_sys_interface_check_fullmsg" | grep -qF 'SMT vulnerable'; then
                 pvulnstatus "$cve" VULN "SMT (HyperThreading) must be disabled for full mitigation"
+            elif echo "$ret_sys_interface_check_fullmsg" | grep -qF 'SMT Host state unknown'; then
+                # The kernel appends "SMT Host state unknown" when running under a
+                # hypervisor (X86_FEATURE_HYPERVISOR): the host controls SMT
+                # scheduling, so it can't be determined from inside the guest (#343).
+                pvulnstatus "$cve" UNK "TAA is mitigated and TSX is disabled, but SMT (Hyper-Threading) cross-thread protection can't be verified from inside a VM guest: it depends on the hypervisor host's SMT/core-scheduling configuration"
             else
                 pvulnstatus "$cve" "$status" "$msg"
             fi

src/vulns/CVE-2023-20593.sh

@@ -103,13 +103,23 @@ check_CVE_2023_20593_linux() {
             fi
         fi
         if [ "$zenbleed_print_vuln" = 1 ]; then
-            pvulnstatus "$cve" VULN "Your kernel is too old to mitigate Zenbleed and your CPU microcode doesn't mitigate it either"
+            if [ "$g_mode" = live ] && is_running_as_guest; then
-            explain "Your CPU vendor may have a new microcode for your CPU model that mitigates this issue (refer to the hardware section above).\n " \
+                # Both Zenbleed mitigations are applied at the host level: an
-                "Otherwise, the Linux kernel is able to mitigate this issue regardless of the microcode version you have, but in this case\n " \
+                # up-to-date microcode, or the host kernel setting FP_BACKUP_FIX
-                "your kernel is too old to support this, your Linux distribution vendor might have a more recent version you should upgrade to.\n " \
+                # in DE_CFG. From inside a guest we can't read that MSR and can't
-                "Note that either having an up to date microcode OR an up to date kernel is enough to mitigate this issue.\n " \
+                # trust the microcode version the hypervisor presents, so we can't
-                "To manually mitigate the issue right now, you may use the following command: \`wrmsr -a 0xc0011029 \$((\$(rdmsr -c 0xc0011029) | (1<<9)))\`,\n " \
+                # confirm or deny the mitigation -- don't cry VULN (#488).
-                "however note that this manual mitigation will only be active until the next reboot."
+                pvulnstatus "$cve" UNK "Zenbleed mitigation can't be verified from inside a VM guest ($g_is_guest_vm_reason): it may be applied by the hypervisor host, but that isn't observable from here"
+                explain "Zenbleed is mitigated either by an up-to-date CPU microcode or by the host kernel setting the FP_BACKUP_FIX bit (DE_CFG MSR 0xc0011029 bit 9). Both are host-level: a guest can neither read that MSR nor trust the microcode version the hypervisor presents (see the VM note in the hardware section above). Re-run this script on the hypervisor host to get an accurate result."
+            else
+                pvulnstatus "$cve" VULN "Your kernel is too old to mitigate Zenbleed and your CPU microcode doesn't mitigate it either"
+                explain "Your CPU vendor may have a new microcode for your CPU model that mitigates this issue (refer to the hardware section above).\n " \
+                    "Otherwise, the Linux kernel is able to mitigate this issue regardless of the microcode version you have, but in this case\n " \
+                    "your kernel is too old to support this, your Linux distribution vendor might have a more recent version you should upgrade to.\n " \
+                    "Note that either having an up to date microcode OR an up to date kernel is enough to mitigate this issue.\n " \
+                    "To manually mitigate the issue right now, you may use the following command: \`wrmsr -a 0xc0011029 \$((\$(rdmsr -c 0xc0011029) | (1<<9)))\`,\n " \
+                    "however note that this manual mitigation will only be active until the next reboot."
+            fi
         fi
         unset zenbleed_print_vuln
     else