add detection of retpoline-aware compiler

Remove superfluous 'YES' output when checking cpuinfo

spectre-meltdown-checker.sh

@@ -1,7 +1,7 @@
 #! /bin/sh
 # Spectre & Meltdown checker
 # Stephane Lesimple
-VERSION=0.13
+VERSION=0.14
 
 # print status function
 pstatus()
@@ -171,15 +171,20 @@ if [ ! -e /sys/kernel/debug/sched_features ]; then
 	# try to mount the debugfs hierarchy ourselves and remember it to umount afterwards
 	mount -t debugfs debugfs /sys/kernel/debug 2>/dev/null && mounted_debugfs=1
 fi
-if [ -e /sys/kernel/debug/ibrs_enabled -o -e /sys/kernel/debug/x86/ibrs_enabled ]; then
+if [ -e /sys/kernel/debug/ibrs_enabled ]; then
 	# if the file is there, we have IBRS compiled-in
 	pstatus green YES
 	ibrs_supported=1
+	ibrs_enabled=$(cat /sys/kernel/debug/ibrs_enabled 2>/dev/null)
+elif [ -e /sys/kernel/debug/x86/ibrs_enabled ]; then
+	# RedHat uses a different path (see https://access.redhat.com/articles/3311301)
+	pstatus green YES
+	ibrs_supported=1
+	ibrs_enabled=$(cat /sys/kernel/debug/x86/ibrs_enabled 2>/dev/null)
 else
 	pstatus red NO
 fi
 
-[ -f /sys/kernel/debug/ibrs_enabled ] && ibrs_enabled=$(cat /sys/kernel/debug/ibrs_enabled 2>/dev/null) || ibrs_enabled=$(cat /sys/kernel/debug/x86/ibrs_enabled 2>/dev/null)
 /bin/echo -n "*   IBRS enabled for Kernel space: "
 # 0 means disabled
 # 1 is enabled only for kernel space
@@ -196,19 +201,12 @@ case "$ibrs_enabled" in
 	"") [ "$ibrs_supported" = 1 ] && pstatus yellow UNKNOWN || pstatus red NO;;
 	0 | 1) pstatus red NO;;
 	2) pstatus green YES;;
-	*) pstatus yellow unknown;;
+	*) pstatus yellow UNKNOWN;;
 esac
 
-if [ "$mounted_debugfs" = 1 ]; then
-	# umount debugfs if we did mount it ourselves
-	umount /sys/kernel/debug
-fi
-
 /bin/echo "* Mitigation 2"
-/bin/echo -n "*   Kernel compiled with retpolines: "
+/bin/echo -n "*   Kernel compiled with retpoline option: "
 # We check the RETPOLINE kernel options
-# XXX this doesn't mean the kernel has been compiled with a retpoline-aware gcc
-# still looking for a way do detect that ...
 if [ -e /proc/config.gz ]; then
 	# either the running kernel exports his own config
 	if zgrep -q '^CONFIG_RETPOLINE=y' /proc/config.gz; then
@@ -229,15 +227,71 @@ else
 	pstatus yellow UNKNOWN "couldn't read your kernel configuration"
 fi
 
+/bin/echo -n "*   Kernel compiled with a retpoline-aware compiler: "
+# Now check if the compiler used to compile the kernel knows how to insert retpolines in generated asm
+# For gcc, this is -mindirect-branch=thunk-extern (detected by the kernel makefiles)
+# See gcc commit https://github.com/hjl-tools/gcc/commit/23b517d4a67c02d3ef80b6109218f2aadad7bd79
+# We'll look for the presence of 'retpoline_call_target' in symbols
+if [ -n "$vmlinux" ]; then
+	# look for the symbol
+	if which nm >/dev/null 2>&1; then
+		# the proper way: use nm and look for the symbol
+		if nm "$vmlinux" 2>/dev/null | grep -qw retpoline_call_target; then
+			retpoline_compiler=1
+			pstatus green YES "retpoline_call_target found"
+		fi
+	else
+		# if we don't have nm, nevermind, the symbol name is long enough to not have
+		# any false positive using good old grep directly on the binary
+		if grep -q retpoline_call_target "$vmlinux"; then
+			retpoline_compiler=1
+			pstatus green YES "retpoline_call_target found"
+		fi
+	fi
+	if [ "$retpoline_compiler" != 1 ]; then
+		# still not ? maybe we just don't have symbols in the kernel image (stripped)
+		# let's objdump it and look for the asm sequence (here for 64 bits)
+		#
+		# ffffffff81000350 <__x86.indirect_thunk>:
+		# ffffffff81000350:       e8 05 00 00 00          callq  ffffffff8100035a <retpoline_call_target>
+		# ffffffff81000355:       0f ae e8                lfence 
+		# ffffffff81000358:       eb fb                   jmp    ffffffff81000355 <__x86.indirect_thunk+0x5>
+
+		# ffffffff8100035a <retpoline_call_target>:
+		# ffffffff8100035a:       48 8d 64 24 08          lea    0x8(%rsp),%rsp
+		# ffffffff8100035f:       c3                      retq   
+		#
+		if ! which perl >/dev/null 2>&1; then
+			pstatus yellow UNKNOWN "missing 'perl', please install it"
+		else
+			# directly look for the opcode sequence in the binary
+			# 64 bits version
+			if perl -ne '/\xe8\x05\x00\x00\x00\x0f\xae\xe8\xeb\xfb\x48\x8d\x64\x24\x08\xc3/ and $found=1; END { exit($found ? 0 : 1) }' "$vmlinux"; then
+				retpoline_compiler=1
+				pstatus green YES "retpoline 64 bits asm sequence found"
+			#elif perl -ne ... 32 bits version of retpoline asm seq
+			# TODO
+			#	retpoline_compiler=1
+			#	pstatus green YES "retpoline 33 bits asm sequence found"
+			else
+				pstatus red NO
+			fi
+		fi
+	fi
+else
+	pstatus yellow UNKNOWN "couldn't find your kernel image"
+fi
+
+
 /bin/echo -ne "> \033[46m\033[30mSTATUS:\033[0m "
 if grep -q AMD /proc/cpuinfo; then
 	pstatus green "NOT VULNERABLE" "your CPU is not vulnerable as per the vendor"
 elif [ "$ibrs_enabled" = 1 -o "$ibrs_enabled" = 2 ]; then
 	pstatus green "NOT VULNERABLE" "IBRS mitigates the vulnerability"
-elif [ "$retpoline" = 1 ]; then
+elif [ "$retpoline" = 1 -a "$retpoline_compiler" = 1 ]; then
-	pstatus green "NOT VULNERABLE" "retpolines mitigate the vulnerability"
+	pstatus green "NOT VULNERABLE" "retpoline mitigate the vulnerability"
 else
-	pstatus red VULNERABLE "IBRS hardware + kernel support OR kernel with retpolines are needed to mitigate the vulnerability"
+	pstatus red VULNERABLE "IBRS hardware + kernel support OR kernel with retpoline are needed to mitigate the vulnerability"
 fi
 
 ##########
@@ -250,13 +304,13 @@ kpti_can_tell=0
 if [ -e /proc/config.gz ]; then
 	# either the running kernel exports his own config
 	kpti_can_tell=1
-	if zgrep -q '^CONFIG_PAGE_TABLE_ISOLATION=y' /proc/config.gz; then
+	if zgrep -q '^\(CONFIG_PAGE_TABLE_ISOLATION=y\|CONFIG_KAISER=y\)' /proc/config.gz; then
 		kpti_support=1
 	fi
 elif [ -e /boot/config-$(uname -r) ]; then
 	# or we can find a config file in /root with the kernel release name
 	kpti_can_tell=1
-	if grep  -q '^CONFIG_PAGE_TABLE_ISOLATION=y' /boot/config-$(uname -r); then
+	if grep  -q '^\(CONFIG_PAGE_TABLE_ISOLATION=y\|CONFIG_KAISER=y\)' /boot/config-$(uname -r); then
 		kpti_support=1
 	fi
 fi
@@ -288,19 +342,30 @@ fi
 /bin/echo -n "* PTI enabled and active: "
 if grep ^flags /proc/cpuinfo | grep -qw pti; then
 	# vanilla PTI patch sets the 'pti' flag in cpuinfo
-	pstatus green YES
 	kpti_enabled=1
+elif grep ^flags /proc/cpuinfo | grep -qw kaiser; then
+	# kernel line 4.9 sets the 'kaiser' flag in cpuinfo
+	kpti_enabled=1
+elif [ -e /sys/kernel/debug/x86/pti_enabled ]; then
+	# RedHat Backport creates a dedicated file, see https://access.redhat.com/articles/3311301
+	kpti_enabled=$(cat /sys/kernel/debug/x86/pti_enabled 2>/dev/null)
 elif dmesg | grep -Eq 'Kernel/User page tables isolation: enabled|Kernel page table isolation enabled'; then
 	# if we can't find the flag, grep in dmesg
-	pstatus green YES
-	kpti_enabled=1
-elif [ -e /sys/kernel/debug/x86/pti_enabled -a "$(cat /sys/kernel/debug/x86/pti_enabled 2>/dev/null)" = 1 ]; then
-	pstatus green YES
 	kpti_enabled=1
+else
+	kpti_enabled=0
+fi
+if [ "$kpti_enabled" = 1 ]; then
+	pstatus green YES
 else
 	pstatus red NO
 fi
 
+if [ "$mounted_debugfs" = 1 ]; then
+	# umount debugfs if we did mount it ourselves
+	umount /sys/kernel/debug
+fi
+
 /bin/echo -ne "> \033[46m\033[30mSTATUS:\033[0m "
 if grep -q AMD /proc/cpuinfo; then
 	pstatus green "NOT VULNERABLE" "your CPU is not vulnerable as per the vendor"