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detect if the used compiler supports retpoline (WIP)

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This commit is contained in:
Stéphane Lesimple 2018-01-08 15:45:09 +01:00
parent f8ca11e56a
commit 207168e097
1 changed files with 49 additions and 3 deletions
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52
spectre-meltdown-checker.sh
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@ -201,14 +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
/bin/echo "* Mitigation 2"
/bin/echo -n "* Kernel compiled with retpolines: "
# 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
@ -229,6 +227,54 @@ else
pstatus yellow UNKNOWN "couldn't read your kernel configuration"
fi
/bin/echo -n "* Kernel compiled with a retpolines-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
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 "$vmlinux"; then
retpoline_compiler=1
pstatus green YES
fi
fi
if [ "$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 objdump >/dev/null 2>&1; then
pstatus yellow UNKNOWN "missing 'objdump' tool, please install it, usually it's in the binutils package"
else
# TODO
# objdump -D "$vmlinux"
# pstatus red NO
# pstatus green YES
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"