fix: hide arch_capabilities_msr_not_read warning under !intel

- /boot may be within a named root subvolume (eg. "/@/boot")
- /boot may be in its own subvolume (eg. "/@boot")

spectre-meltdown-checker.sh

@@ -9,7 +9,7 @@
 #
 # Stephane Lesimple
 #
-VERSION='0.38'
+VERSION='0.39'
 
 trap 'exit_cleanup' EXIT
 trap '_warn "interrupted, cleaning up..."; exit_cleanup; exit 1' INT
@@ -150,12 +150,12 @@ if which printf >/dev/null 2>&1; then
 elif which echo >/dev/null 2>&1; then
 	echo_cmd=$(which echo)
 else
-	# which command is broken?
+	# maybe the `which` command is broken?
 	[ -x /bin/echo        ] && echo_cmd=/bin/echo
 	# for Android
 	[ -x /system/bin/echo ] && echo_cmd=/system/bin/echo
 fi
-# still empty ? fallback to builtin
+# still empty? fallback to builtin
 [ -z "$echo_cmd" ] && echo_cmd=echo
 __echo()
 {
@@ -245,15 +245,13 @@ is_cpu_vulnerable_cached=0
 _is_cpu_vulnerable_cached()
 {
 	# shellcheck disable=SC2086
-	[ "$1" = 1  ] && return $variant1
-	# shellcheck disable=SC2086
-	[ "$1" = 2  ] && return $variant2
-	# shellcheck disable=SC2086
-	[ "$1" = 3  ] && return $variant3
-	# shellcheck disable=SC2086
-	[ "$1" = 3a ] && return $variant3a
-	# shellcheck disable=SC2086
-	[ "$1" = 4  ] && return $variant4
+	{
+		[ "$1" = 1  ] && return $variant1
+		[ "$1" = 2  ] && return $variant2
+		[ "$1" = 3  ] && return $variant3
+		[ "$1" = 3a ] && return $variant3a
+		[ "$1" = 4  ] && return $variant4
+	}
 	echo "$0: error: invalid variant '$1' passed to is_cpu_vulnerable()" >&2
 	exit 255
 }
@@ -889,9 +887,7 @@ load_cpuid()
 }
 
 # shellcheck disable=SC2034
-{
 EAX=1; EBX=2; ECX=3; EDX=4;
-}
 read_cpuid()
 {
 	# leaf is the value of the eax register when calling the cpuid instruction:
@@ -1210,6 +1206,17 @@ is_skylake_cpu()
 	return 1
 }
 
+is_vulnerable_to_empty_rsb()
+{
+	if is_intel && [ -z "$capabilities_rsba" ]; then
+		_warn "is_vulnerable_to_empty_rsb() called before ARCH CAPABILITIES MSR was read"
+	fi
+	if is_skylake_cpu || [ "$capabilities_rsba" = 1 ]; then
+		return 0
+	fi
+	return 1
+}
+
 is_zen_cpu()
 {
 	# is this CPU from the AMD ZEN family ? (ryzen, epyc, ...)
@@ -1247,6 +1254,8 @@ if [ "$opt_hw_only" = 1 ]; then
 		opt_variant1=0
 		opt_variant2=0
 		opt_variant3=0
+		opt_variant3a=0
+		opt_variant4=0
 	fi
 fi
 
@@ -1309,6 +1318,9 @@ if [ "$opt_live" = 1 ]; then
 	if [ -r /proc/cmdline ] && grep -q 'BOOT_IMAGE=' /proc/cmdline; then
 		opt_kernel=$(grep -Eo 'BOOT_IMAGE=[^ ]+' /proc/cmdline | cut -d= -f2)
 		_debug "found opt_kernel=$opt_kernel in /proc/cmdline"
+		# if the boot partition is within a btrfs subvolume, strip the subvolume name
+		# if /boot is a separate subvolume, the remainder of the code in this section should handle it
+		if echo "$opt_kernel" | grep -q "^/@"; then opt_kernel=$(echo "$opt_kernel" | sed "s:/@[^/]*::"); fi
 		# if we have a dedicated /boot partition, our bootloader might have just called it /
 		# so try to prepend /boot and see if we find anything
 		[ -e "/boot/$opt_kernel" ] && opt_kernel="/boot/$opt_kernel"
@@ -1327,6 +1339,8 @@ if [ "$opt_live" = 1 ]; then
 		[ -e "/boot/vmlinuz-linux"       ] && opt_kernel="/boot/vmlinuz-linux"
 		# Arch aarch64:
 		[ -e "/boot/Image"               ] && opt_kernel="/boot/Image"
+		# Arch armv5/armv7:
+		[ -e "/boot/zImage"              ] && opt_kernel="/boot/zImage"
 		# Linux-Libre:
 		[ -e "/boot/vmlinuz-linux-libre" ] && opt_kernel="/boot/vmlinuz-linux-libre"
 		# pine64
@@ -1494,18 +1508,39 @@ number_of_cpus()
 # $2 - cpu index
 write_msr()
 {
+	# _msr must be in hex, in the form 0x1234:
+	_msr="$1"
+	# cpu index, starting from 0:
+	_cpu="$2"
 	if [ "$os" != Linux ]; then
-		cpucontrol -m "$1=0" "/dev/cpuctl$2" >/dev/null 2>&1; ret=$?
+		cpucontrol -m "$_msr=0" "/dev/cpuctl$_cpu" >/dev/null 2>&1; ret=$?
 	else
+		# for Linux
 		# convert to decimal
-		_msrindex=$(( $1 ))
-		if [ ! -w /dev/cpu/"$2"/msr ]; then
+		_msr=$(( _msr ))
+		if [ ! -w /dev/cpu/"$_cpu"/msr ]; then
 			ret=200 # permission error
+		# if wrmsr is available, use it
+		elif which wrmsr >/dev/null 2>&1 && [ "$SMC_NO_WRMSR" != 1 ]; then
+			_debug "write_msr: using wrmsr"
+			wrmsr $_msr 0 2>/dev/null; ret=$?
+		# or if we have perl, use it, any 5.x version will work
+		elif which perl >/dev/null 2>&1 && [ "$SMC_NO_PERL" != 1 ]; then
+			_debug "write_msr: using perl"
+			ret=1
+			perl -e "open(M,'>','/dev/cpu/$_cpu/msr') and seek(M,$_msr,0) and exit(syswrite(M,pack('H16',0)))"; [ $? -eq 8 ] && ret=0
+		# fallback to dd if it supports seek_bytes
+		elif dd if=/dev/null of=/dev/null bs=8 count=1 seek="$_msr" oflag=seek_bytes 2>/dev/null; then
+			_debug "write_msr: using dd"
+			dd if=/dev/zero of=/dev/cpu/"$_cpu"/msr bs=8 count=1 seek="$_msr" oflag=seek_bytes 2>/dev/null; ret=$?
 		else
-			dd if=/dev/zero of=/dev/cpu/"$2"/msr bs=8 count=1 seek="$_msrindex" oflag=seek_bytes 2>/dev/null; ret=$?
+			_debug "write_msr: got no wrmsr, perl or recent enough dd!"
+			return 201 # missing tool error
 		fi
 	fi
-	_debug "write_msr: for cpu $2 on msr $1 ($_msrindex), ret=$ret"
+	# normalize ret
+	[ "$ret" != 0 ] && ret=1
+	_debug "write_msr: for cpu $_cpu on msr $_msr, ret=$ret"
 	return $ret
 }
 
@@ -1526,12 +1561,27 @@ read_msr()
 		_msr_l="$(( _msr_l >> 24 & 0xFF )) $(( _msr_l >> 16 & 0xFF )) $(( _msr_l >> 8 & 0xFF )) $(( _msr_l & 0xFF ))"
 		read_msr_value="$_msr_h $_msr_l"
 	else
+		# for Linux
 		# convert to decimal
 		_msr=$(( _msr ))
 		if [ ! -r /dev/cpu/"$_cpu"/msr ]; then
 			return 200 # permission error
+		# if rdmsr is available, use it
+		elif which rdmsr >/dev/null 2>&1 && [ "$SMC_NO_RDMSR" != 1 ]; then
+			_debug "read_msr: using rdmsr"
+			read_msr_value=$(rdmsr -r $_msr 2>/dev/null | od -t u8 -A n)
+		# or if we have perl, use it, any 5.x version will work
+		elif which perl >/dev/null 2>&1 && [ "$SMC_NO_PERL" != 1 ]; then
+			_debug "read_msr: using perl"
+			read_msr_value=$(perl -e "open(M,'<','/dev/cpu/$_cpu/msr') and seek(M,$_msr,0) and read(M,\$_,8) and print" | od -t u8 -A n)
+		# fallback to dd if it supports skip_bytes
+		elif dd if=/dev/null of=/dev/null bs=8 count=1 skip="$_msr" iflag=skip_bytes 2>/dev/null; then
+			_debug "read_msr: using dd"
+			read_msr_value=$(dd if=/dev/cpu/"$_cpu"/msr bs=8 count=1 skip="$_msr" iflag=skip_bytes 2>/dev/null | od -t u8 -A n)
+		else
+			_debug "read_msr: got no rdmsr, perl or recent enough dd!"
+			return 201 # missing tool error
 		fi
-		read_msr_value=$(dd if=/dev/cpu/"$_cpu"/msr bs=8 count=1 skip="$_msr" iflag=skip_bytes 2>/dev/null | od -t u1 -A n)
 		if [ -z "$read_msr_value" ]; then
 			# MSR doesn't exist, don't check for $? because some versions of dd still return 0!
 			return 1
@@ -1564,9 +1614,7 @@ check_cpu()
 		pstatus yellow UNKNOWN "is msr kernel module available?"
 	else
 		# the new MSR 'SPEC_CTRL' is at offset 0x48
-		# here we use dd, it's the same as using 'rdmsr 0x48' but without needing the rdmsr tool
-		# if we get a read error, the MSR is not there. bs has to be 8 for msr
-		# skip=9 because 8*9=72=0x48
+		# we check if we have it for all cpus
 		val=0
 		cpu_mismatch=0
 		for i in $(seq 0 "$idx_max_cpu")
@@ -1593,6 +1641,9 @@ check_cpu()
 		elif [ $val -eq 200 ]; then
 			pstatus yellow UNKNOWN "is msr kernel module available?"
 			spec_ctrl_msr=-1
+		elif [ $val -eq 201 ]; then
+			pstatus yellow UNKNOWN "missing tool, install either msr-tools or perl"
+			spec_ctrl_msr=-1
 		else
 			spec_ctrl_msr=0
 			pstatus yellow NO
@@ -1654,8 +1705,7 @@ check_cpu()
 		pstatus yellow UNKNOWN "is msr kernel module available?"
 	else
 		# the new MSR 'PRED_CTRL' is at offset 0x49, write-only
-		# here we use dd, it's the same as using 'wrmsr 0x49 0' but without needing the wrmsr tool
-		# if we get a write error, the MSR is not there
+		# we test if of all cpus
 		val=0
 		cpu_mismatch=0
 		for i in $(seq 0 "$idx_max_cpu")
@@ -1816,27 +1866,28 @@ check_cpu()
 		capabilities_rdcl_no=-1
 		capabilities_ibrs_all=-1
 		capabilities_ssb_no=-1
+		capabilities_rsba=-1
 		if [ "$cpuid_arch_capabilities" = -1 ]; then
 			pstatus yellow UNKNOWN
 		elif [ "$cpuid_arch_capabilities" != 1 ]; then
 			capabilities_rdcl_no=0
 			capabilities_ibrs_all=0
 			capabilities_ssb_no=0
+			capabilities_rsba=0
 			pstatus yellow NO
 		elif [ ! -e /dev/cpu/0/msr ] && [ ! -e /dev/cpuctl0 ]; then
 			spec_ctrl_msr=-1
 			pstatus yellow UNKNOWN "is msr kernel module available?"
 		else
 			# the new MSR 'ARCH_CAPABILITIES' is at offset 0x10a
-			# here we use dd, it's the same as using 'rdmsr 0x10a' but without needing the rdmsr tool
-			# if we get a read error, the MSR is not there. bs has to be 8 for msr
+			# we check if we have it for all cpus
 			val=0
 			val_cap_msr=0
 			cpu_mismatch=0
 			for i in $(seq 0 "$idx_max_cpu")
 			do
 				read_msr 0x10a "$i"; ret=$?
-				capabilities=$(echo "$read_msr_value" | awk '{print $8}')
+				capabilities=$read_msr_value
 				if [ "$i" -eq 0 ]; then
 					val=$ret
 					val_cap_msr=$capabilities
@@ -1852,12 +1903,14 @@ check_cpu()
 			capabilities_rdcl_no=0
 			capabilities_ibrs_all=0
 			capabilities_ssb_no=0
+			capabilities_rsba=0
 			if [ $val -eq 0 ]; then
-				_debug "capabilities MSR lower byte is $capabilities (decimal)"
-				[ $(( capabilities &  1 )) -eq 1  ] && capabilities_rdcl_no=1
-				[ $(( capabilities &  2 )) -eq 2  ] && capabilities_ibrs_all=1
-				[ $(( capabilities & 16 )) -eq 16 ] && capabilities_ssb_no=1
-				_debug "capabilities says rdcl_no=$capabilities_rdcl_no ibrs_all=$capabilities_ibrs_all ssb_no=$capabilities_ssb_no"
+				_debug "capabilities MSR is $capabilities (decimal)"
+				[ $(( capabilities >> 0 & 1 )) -eq 1 ] && capabilities_rdcl_no=1
+				[ $(( capabilities >> 1 & 1 )) -eq 1 ] && capabilities_ibrs_all=1
+				[ $(( capabilities >> 2 & 1 )) -eq 1 ] && capabilities_rsba=1
+				[ $(( capabilities >> 4 & 1 )) -eq 1 ] && capabilities_ssb_no=1
+				_debug "capabilities says rdcl_no=$capabilities_rdcl_no ibrs_all=$capabilities_ibrs_all ssb_no=$capabilities_ssb_no rsba=$capabilities_rsba"
 				if [ "$capabilities_ibrs_all" = 1 ]; then
 					if [ $cpu_mismatch -eq 0 ]; then
 						pstatus green YES
@@ -1869,6 +1922,8 @@ check_cpu()
 				fi
 			elif [ $val -eq 200 ]; then
 				pstatus yellow UNKNOWN "is msr kernel module available?"
+			elif [ $val -eq 201 ]; then
+				pstatus yellow UNKNOWN "missing tool, install either msr-tools or perl"
 			else
 				pstatus yellow NO
 			fi
@@ -1893,6 +1948,15 @@ check_cpu()
 		pstatus yellow NO
 	fi
 
+	_info_nol "  * Hypervisor indicates host CPU might be vulnerable to RSB underflow (RSBA): "
+	if [ "$capabilities_rsba" = -1 ]; then
+		pstatus yellow UNKNOWN
+	elif [ "$capabilities_rsba" = 1 ]; then
+		pstatus yellow YES
+	else
+		pstatus blue NO
+	fi
+
 	_info_nol "  * CPU microcode is known to cause stability problems: "
 	if is_ucode_blacklisted; then
 		pstatus red YES "$ucode_found"
@@ -2514,7 +2578,7 @@ check_variant2_linux()
 			fi
 		fi
 
-		if is_skylake_cpu || [ "$opt_verbose" -ge 2 ]; then
+		if is_vulnerable_to_empty_rsb || [ "$opt_verbose" -ge 2 ]; then
 			_info_nol "  * Kernel supports RSB filling: "
 			if ! which "${opt_arch_prefix}strings" >/dev/null 2>&1; then
 				pstatus yellow UNKNOWN "missing '${opt_arch_prefix}strings' tool, please install it, usually it's in the binutils package"
@@ -2541,9 +2605,9 @@ check_variant2_linux()
 		# override status & msg in case CPU is not vulnerable after all
 		pvulnstatus $cve OK "your CPU vendor reported your CPU model as not vulnerable"
 	else
-		if [ "$retpoline" = 1 ] && [ "$retpoline_compiler" = 1 ] && [ "$retp_enabled" != 0 ] && [ -n "$ibpb_enabled" ] && [ "$ibpb_enabled" -ge 1 ] && ( ! is_skylake_cpu || [ -n "$rsb_filling" ] ); then
+		if [ "$retpoline" = 1 ] && [ "$retpoline_compiler" = 1 ] && [ "$retp_enabled" != 0 ] && [ -n "$ibpb_enabled" ] && [ "$ibpb_enabled" -ge 1 ] && ( ! is_vulnerable_to_empty_rsb || [ -n "$rsb_filling" ] ); then
 			pvulnstatus $cve OK "Full retpoline + IBPB are mitigating the vulnerability"
-		elif [ "$retpoline" = 1 ] && [ "$retpoline_compiler" = 1 ] && [ "$retp_enabled" != 0 ] && [ "$opt_paranoid" = 0 ] && ( ! is_skylake_cpu || [ -n "$rsb_filling" ] ); then
+		elif [ "$retpoline" = 1 ] && [ "$retpoline_compiler" = 1 ] && [ "$retp_enabled" != 0 ] && [ "$opt_paranoid" = 0 ] && ( ! is_vulnerable_to_empty_rsb || [ -n "$rsb_filling" ] ); then
 			pvulnstatus $cve OK "Full retpoline is mitigating the vulnerability"
 			if [ -n "$cpuid_ibpb" ]; then
 				_warn "You should enable IBPB to complete retpoline as a Variant 2 mitigation"
@@ -2573,7 +2637,7 @@ check_variant2_linux()
 		# if we arrive here and didn't already call pvulnstatus, then it's VULN, let's explain why
 		if [ "$pvulnstatus_last_cve" != "$cve" ]; then
 			# explain what's needed for this CPU
-			if is_skylake_cpu; then
+			if is_vulnerable_to_empty_rsb; then
 				pvulnstatus $cve VULN "IBRS+IBPB or retpoline+IBPB+RBS filling, is needed to mitigate the vulnerability"
 				explain "To mitigate this vulnerability, you need either IBRS + IBPB, both requiring hardware support from your CPU microcode in addition to kernel support, or a kernel compiled with retpoline and IBPB, with retpoline requiring a retpoline-aware compiler (re-run this script with -v to know if your version of gcc is retpoline-aware) and IBPB requiring hardware support from your CPU microcode. You also need a recent-enough kernel that supports RSB filling if you plan to use retpoline. For Skylake+ CPUs, the IBRS + IBPB approach is generally preferred as it guarantees complete protection, and the performance impact is not as high as with older CPUs in comparison with retpoline. More information about how to enable the missing bits for those two possible mitigations on your system follow. You only need to take one of the two approaches."
 			elif is_zen_cpu; then