From 93de2a6a4b91b72607136dd656edf03fb399d27f Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 23 Sep 2026 09:37:21 -0700 Subject: KVM: SEV: Do cache maintenance on the source VM during intra-host migration Manually perform cache maintenance on the source VM during intra-host migration to ensure no stale data is left in CPU caches after the VM is destroyed. Because the source VM is "converted" to a non-SEV VM, KVM's memory reclaim flows won't trigger cache maintenance, e.g. when all guest memory is reclaimed in response to detaching from the mmu_notifier. Note, relying on the destination VM to do cache maintenance isn't an option as KVM doesn't require identical guest memory configurations, i.e. the source VM may have access to memory that the destination VM does not. Enforcing equivalent memory configurations is infeasible, as it would require a *deep* comparison of memslots, e.g. to verify that not only are the memslot identical, but what the memslots point at is also identical. Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- scripts/check_extable.sh | 147 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 147 insertions(+) create mode 100755 scripts/check_extable.sh (limited to 'scripts/check_extable.sh') diff --git a/scripts/check_extable.sh b/scripts/check_extable.sh new file mode 100755 index 000000000..4b380564c --- /dev/null +++ b/scripts/check_extable.sh @@ -0,0 +1,147 @@ +#! /bin/bash +# SPDX-License-Identifier: GPL-2.0 +# (c) 2015, Quentin Casasnovas + +obj=$1 + +file ${obj} | grep -q ELF || (echo "${obj} is not an ELF file." 1>&2 ; exit 0) + +# Bail out early if there isn't an __ex_table section in this object file. +objdump -hj __ex_table ${obj} 2> /dev/null > /dev/null +[ $? -ne 0 ] && exit 0 + +white_list=.text,.fixup + +suspicious_relocs=$(objdump -rj __ex_table ${obj} | tail -n +6 | + grep -v $(eval echo -e{${white_list}}) | awk '{print $3}') + +# No suspicious relocs in __ex_table, jobs a good'un +[ -z "${suspicious_relocs}" ] && exit 0 + + +# After this point, something is seriously wrong since we just found out we +# have some relocations in __ex_table which point to sections which aren't +# white listed. If you're adding a new section in the Linux kernel, and +# you're expecting this section to contain code which can fault (i.e. the +# __ex_table relocation to your new section is expected), simply add your +# new section to the white_list variable above. If not, you're probably +# doing something wrong and the rest of this code is just trying to print +# you more information about it. + +function find_section_offset_from_symbol() +{ + eval $(objdump -t ${obj} | grep ${1} | sed 's/\([0-9a-f]\+\) .\{7\} \([^ \t]\+\).*/section="\2"; section_offset="0x\1" /') + + # addr2line takes addresses in hexadecimal... + section_offset=$(printf "0x%016x" $(( ${section_offset} + $2 )) ) +} + +function find_symbol_and_offset_from_reloc() +{ + # Extract symbol and offset from the objdump output + eval $(echo $reloc | sed 's/\([^+]\+\)+\?\(0x[0-9a-f]\+\)\?/symbol="\1"; symbol_offset="\2"/') + + # When the relocation points to the begining of a symbol or section, it + # won't print the offset since it is zero. + if [ -z "${symbol_offset}" ]; then + symbol_offset=0x0 + fi +} + +function find_alt_replacement_target() +{ + # The target of the .altinstr_replacement is the relocation just before + # the .altinstr_replacement one. + eval $(objdump -rj .altinstructions ${obj} | grep -B1 "${section}+${section_offset}" | head -n1 | awk '{print $3}' | + sed 's/\([^+]\+\)+\(0x[0-9a-f]\+\)/alt_target_section="\1"; alt_target_offset="\2"/') +} + +function handle_alt_replacement_reloc() +{ + # This will define alt_target_section and alt_target_section_offset + find_alt_replacement_target ${section} ${section_offset} + + echo "Error: found a reference to .altinstr_replacement in __ex_table:" + addr2line -fip -j ${alt_target_section} -e ${obj} ${alt_target_offset} | awk '{print "\t" $0}' + + error=true +} + +function is_executable_section() +{ + objdump -hwj ${section} ${obj} | grep -q CODE + return $? +} + +function handle_suspicious_generic_reloc() +{ + if is_executable_section ${section}; then + # We've got a relocation to a non white listed _executable_ + # section, print a warning so the developper adds the section to + # the white list or fix his code. We try to pretty-print the file + # and line number where that relocation was added. + echo "Warning: found a reference to section \"${section}\" in __ex_table:" + addr2line -fip -j ${section} -e ${obj} ${section_offset} | awk '{print "\t" $0}' + else + # Something is definitively wrong here since we've got a relocation + # to a non-executable section, there's no way this would ever be + # running in the kernel. + echo "Error: found a reference to non-executable section \"${section}\" in __ex_table at offset ${section_offset}" + error=true + fi +} + +function handle_suspicious_reloc() +{ + case "${section}" in + ".altinstr_replacement") + handle_alt_replacement_reloc ${section} ${section_offset} + ;; + *) + handle_suspicious_generic_reloc ${section} ${section_offset} + ;; + esac +} + +function diagnose() +{ + + for reloc in ${suspicious_relocs}; do + # Let's find out where the target of the relocation in __ex_table + # is, this will define ${symbol} and ${symbol_offset} + find_symbol_and_offset_from_reloc ${reloc} + + # When there's a global symbol at the place of the relocation, + # objdump will use it instead of giving us a section+offset, so + # let's find out which section is this symbol in and the total + # offset withing that section. + find_section_offset_from_symbol ${symbol} ${symbol_offset} + + # In this case objdump was presenting us with a reloc to a symbol + # rather than a section. Now that we've got the actual section, + # we can skip it if it's in the white_list. + if [ -z "$( echo $section | grep -v $(eval echo -e{${white_list}}))" ]; then + continue; + fi + + # Will either print a warning if the relocation happens to be in a + # section we do not know but has executable bit set, or error out. + handle_suspicious_reloc + done +} + +function check_debug_info() { + objdump -hj .debug_info ${obj} 2> /dev/null > /dev/null || + echo -e "${obj} does not contain debug information, the addr2line output will be limited.\n" \ + "Recompile ${obj} with CONFIG_DEBUG_INFO to get a more useful output." +} + +check_debug_info + +diagnose + +if [ "${error}" ]; then + exit 1 +fi + +exit 0 -- cgit v1.3.1