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

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 grep -qw avx512 "$g_procfs/cpuinfo" 2>/dev/null; then cap_avx512=1; fi
+        if cpuinfo_has_flag avx2; then cap_avx2=1; fi
+        if cpuinfo_has_flag avx512; then cap_avx512=1; fi
         cpu_vendor=$(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/400_hw_check.sh

@@ -513,7 +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"
@@ -588,7 +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 $g_procfs/cpuinfo"
@@ -661,7 +661,7 @@ check_cpu() {
     fi
     if [ -z "$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
@@ -733,9 +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
@@ -795,7 +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
@@ -815,7 +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"
@@ -885,7 +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
@@ -987,8 +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

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 [ "$opt_paranoid" = 1 ]; then
-            pvulnstatus "$cve" VULN "$unk, and no BSD mitigation exists"
-            explain "There is no known mitigation for this CPU model. Even with up-to-date microcode, BSD kernels do not invoke VERW for MMIO Stale Data clearing. Only a hardware replacement can fully address this."
+        if is_arch_cap_mmio_undetermined; then
+            # We only landed in the "unknown" bucket because the IA32_ARCH_CAPABILITIES
+            # MSR couldn't be read: the CPU might actually advertise MMIO immunity.
+            unk="your CPU's MMIO Stale Data status could not be determined: the IA32_ARCH_CAPABILITIES MSR (0x10a) couldn't be read"
+            pvulnstatus "$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 "$kernel_mmio"
@@ -241,12 +257,32 @@ check_mmio_linux() {
         # Bypass the normal sysfs reconciliation: sysfs reports "Unknown: No mitigations"
         # only on v6.0-v6.15. On earlier and on v6.16+ kernels it wrongly says "Not affected"
         # for these CPUs (which predate FB_CLEAR microcode and Intel's affected-processor list).
-        unk="your CPU's MMIO Stale Data status is unknown (Intel never officially assessed this CPU, its servicing period has ended)"
-        if [ "$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. Consider replacing affected hardware."
+        if is_arch_cap_mmio_undetermined; then
+            # We landed in the "unknown" bucket only because the IA32_ARCH_CAPABILITIES
+            # MSR couldn't be read from userspace (no msr module, or kernel lockdown under
+            # 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

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 "$EBX" 10 1 1
@@ -110,11 +110,11 @@ check_CVE_2017_5754_linux() {
             dmesg_grep="$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

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"