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fix(variant1): smarter lfence check

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Instead of just counting the number of LFENCE
instructions, now we're only counting the those
that directly follow a jump instruction.
This commit is contained in:
Stéphane Lesimple 2018-01-30 22:59:44 +01:00
parent b738ac4bd7
commit aa18b51e1c
1 changed files with 8 additions and 6 deletions
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14
spectre-meltdown-checker.sh
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@ -1192,7 +1192,7 @@ check_variant1()
if [ "$opt_verbose" -ge 2 ] || [ "$v1_mask_nospec" != 1 ]; then if [ "$opt_verbose" -ge 2 ] || [ "$v1_mask_nospec" != 1 ]; then
# this is a slow heuristic and we don't need it if we already know the kernel is patched # this is a slow heuristic and we don't need it if we already know the kernel is patched
# but still show it in verbose mode # but still show it in verbose mode
_info_nol "* Checking count of LFENCE opcodes in kernel: " _info_nol "* Checking count of LFENCE instructions following a jump in kernel: "
if [ -n "$vmlinux_err" ]; then if [ -n "$vmlinux_err" ]; then
pstatus yellow UNKNOWN "couldn't check ($vmlinux_err)" pstatus yellow UNKNOWN "couldn't check ($vmlinux_err)"
else else
@ -1204,12 +1204,14 @@ check_variant1()
# in patched kernels, this is more around 70-80, sometimes way higher (100+) # in patched kernels, this is more around 70-80, sometimes way higher (100+)
# v0.13: 68 found in a 3.10.23-xxxx-std-ipv6-64 (with lots of modules compiled-in directly), which doesn't have the LFENCE patches, # v0.13: 68 found in a 3.10.23-xxxx-std-ipv6-64 (with lots of modules compiled-in directly), which doesn't have the LFENCE patches,
# so let's push the threshold to 70. # so let's push the threshold to 70.
nb_lfence=$(objdump -d "$vmlinux" | grep -wc 'lfence') # v0.33+: now only count lfence opcodes after a jump, way less error-prone
if [ "$nb_lfence" -lt 70 ]; then # non patched kernel have between 0 and 20 matches, patched ones have at least 40-45
pstatus red NO "only $nb_lfence opcodes found, should be >= 70, heuristic to be improved when official patches become available" nb_lfence=$(objdump -d "$vmlinux" | grep -w -B1 lfence | grep -Ewc 'jmp|jne|je')
if [ "$nb_lfence" -lt 30 ]; then
pstatus red NO "only $nb_lfence jump-then-lfence instructions found, should be >= 30 (heuristic)"
else else
v1_lfence=1 v1_lfence=1
pstatus green YES "$nb_lfence opcodes found, which is >= 70, heuristic to be improved when official patches become available" pstatus green YES "$nb_lfence jump-then-lfence instructions found, which is >= 30 (heuristic)"
fi fi
fi fi
fi fi
@ -1231,7 +1233,7 @@ check_variant1()
if [ "$v1_mask_nospec" = 1 ]; then if [ "$v1_mask_nospec" = 1 ]; then
pvulnstatus $cve OK "Kernel source has been patched to mitigate the vulnerability (array_index_mask_nospec)" pvulnstatus $cve OK "Kernel source has been patched to mitigate the vulnerability (array_index_mask_nospec)"
elif [ "$v1_lfence" = 1 ]; then elif [ "$v1_lfence" = 1 ]; then
pvulnstatus $cve OK "Kernel source has PROBABLY been patched to mitigate the vulnerability (LFENCE opcodes heuristic)" pvulnstatus $cve OK "Kernel source has PROBABLY been patched to mitigate the vulnerability (jump-then-lfence instructions heuristic)"
elif [ "$vmlinux_err" ]; then elif [ "$vmlinux_err" ]; then
pvulnstatus $cve UNK "Couldn't find kernel image or tools missing to execute the checks" pvulnstatus $cve UNK "Couldn't find kernel image or tools missing to execute the checks"
else else