mirror of
https://github.com/dynup/kpatch
synced 2024-12-18 19:34:30 +00:00
Joe Lawrence
GitHub
commit
cd2c3ede75
@ -774,3 +774,92 @@ excellent example and description of this problem with annotated disassembly.
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Adding `__attribute__((optimize("-fno-optimize-sibling-calls")))` instructs
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GCC to turn off the optimization for the given function.
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Exported symbol versioning
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--------------------------
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### Background
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`CONFIG_MODVERSIONS` enables an ABI check between exported kernel symbols and
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modules referencing those symbols, enforced on module load. When building the
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kernel, preprocessor output from `gcc -E` for each source file is passed to
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scripts/genksyms. The genksyms script recursively expands each exported symbol
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to its basic types. A hash is generated for each symbol as it traverses back up
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the symbol tree. The end result is a CRC for each exported function in
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the Module.symvers file and embedded in the vmlinux kernel object itself.
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A similar checksumming is performed when building modules: referenced exported
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symbol CRCs are stored in the module’s `__versions` section (you can also find
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these in plain-text intermediate \*.mod.c files.)
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When the kernel loads a module, the symbol CRCs found in its `__versions` are
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compared to those of the kernel, if the two do not match, the kernel will refuse
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to load it:
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```
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<module>: disagrees about version of symbol <symbol>
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<module>: Unknown symbol <symbol> (err -22)
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```
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### Kpatch detection
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After building the original and patched sources, kpatch-build compares the
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newly calculated Module.symvers against the original. Discrepancies are
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reported:
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```
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ERROR: Version disagreement for symbol <symbol>
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```
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These reports should be addressed to ensure that the resulting kpatch module
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can be loaded.
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#### False positives
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It is rare, but possible for a kpatch to introduce inadvertent symbol CRC
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changes that are not true ABI changes. The following conditions must occur:
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1. The kpatch must modify the definition of an exported symbol. For example,
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introducing a new header file may further define an opaque data type:
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Before the kpatch, compilation unit U from the original kernel build only
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knew about a `struct S` declaration (not its complete type). At the same
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time, U contains function F, which has an interface that references S. If
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the kpatch adds a header file to U that now fully defines `struct S { int
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a, b, c; }`, its symbol type graph changes, CRCs generated for F are updated,
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but its ABI remains consistent.
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2. The kpatch must introduce either a change or reference to F such that it is
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included in the resulting kpatch module. This will force a `__version`
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entry based on the new CRC.
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Note: if a kpatch doesn't change or reference F such that it is **not**
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included in the resulting kpatch module, the new CRC value won't be added
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to the module's `__version` table. However, if a future accumulative patch
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does add a new change or reference to F, the new CRC will become a problem.
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#### Avoidance
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Kpatches should introduce new `#include` directives sparingly. Whenever
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possible, extract the required definitions from header filers into kpatched
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compilation units directly.
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If additional header files or symbol definitions cannot be avoided, consider
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surrounding the offending include/definitions in an `#ifndef __GENKSYMS__`
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macro. The genksyms script will skip over those blocks when performing its CRC
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calculations.
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### But what about a real ABI change?
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If a kpatch introduces a true ABI change, each of calling functions would
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consequently need to be updated in the kpatch module. For unexported functions,
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this may be handled safely if the kpatch does indeed update all callers.
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However, since motivation behind `CONFIG_MODVERSIONS` is to provide basic ABI
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verification between the kernel and modules for **exported** functions, kpatch
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cannot safely change this ABI without worrying about breaking other out-of-tree
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drivers. Those drivers have been built against the reference kernel's original
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set of CRCs and expect the original ABI.
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To track down specifically what caused a symbol CRC change, tools like
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[kabi-dw](https://github.com/skozina/kabi-dw) can be employed to produce a
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detailed symbol definition report. For a kpatch-build, kabi-dw can be modified
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to operate on .o object files (not just .ko and vmlinux files) and the
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`$CACHEDIR/tmp/{orig, patched}` directories compared.
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@ -745,6 +745,7 @@ USE_KLP_ARCH=0
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CONFIG_PARAVIRT=0
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CONFIG_UNWINDER_ORC=0
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CONFIG_JUMP_LABEL=0
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CONFIG_MODVERSIONS=0
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if grep -q "CONFIG_LIVEPATCH=y" "$CONFIGFILE" && (kernel_is_rhel || kernel_version_gte 4.9.0); then
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@ -770,6 +771,7 @@ fi
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grep -q "CONFIG_PARAVIRT=y" "$CONFIGFILE" && CONFIG_PARAVIRT=1
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grep -q "CONFIG_UNWINDER_ORC=y" "$CONFIGFILE" && CONFIG_UNWINDER_ORC=1
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grep -q "CONFIG_JUMP_LABEL=y" "$CONFIGFILE" && CONFIG_JUMP_LABEL=1
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grep -q "CONFIG_MODVERSIONS=y" "$CONFIGFILE" && CONFIG_MODVERSIONS=1
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# unsupported kernel option checking
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grep -q "CONFIG_DEBUG_INFO_SPLIT=y" "$CONFIGFILE" && die "kernel option 'CONFIG_DEBUG_INFO_SPLIT' not supported"
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@ -805,6 +807,9 @@ unset KPATCH_GCC_TEMPDIR
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# shellcheck disable=SC2086
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CROSS_COMPILE="$TOOLSDIR/kpatch-gcc " make "-j$CPUS" $TARGETS 2>&1 | logger || die
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# Save original module symvers
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cp "$SRCDIR/Module.symvers" "$TEMPDIR/Module.symvers"
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echo "Building patched source"
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apply_patches
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mkdir -p "$TEMPDIR/orig" "$TEMPDIR/patched"
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@ -831,6 +836,29 @@ fi
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[[ -n "$OOT_MODULE" ]] || grep -q vmlinux "$SRCDIR/Module.symvers" || die "truncated $SRCDIR/Module.symvers file"
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if [[ "$CONFIG_MODVERSIONS" -eq 1 ]]; then
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while read -ra sym_line; do
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if [[ ${#sym_line[@]} -lt 4 ]]; then
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die "Malformed ${TEMPDIR}/Module.symvers file"
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fi
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sym=${sym_line[1]}
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read -ra patched_sym_line <<< "$(grep "\s$sym\s" "$SRCDIR/Module.symvers")"
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if [[ ${#patched_sym_line[@]} -lt 4 ]]; then
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die "Malformed symbol entry for ${sym} in ${SRCDIR}/Module.symvers file"
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fi
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# Assume that both original and patched symvers have the same format.
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# In both cases, the symbol should have the same CRC, belong to the same
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# Module/Namespace and have the same export type.
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if [[ ${#sym_line[@]} -ne ${#patched_sym_line[@]} || \
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"${sym_line[*]}" != "${patched_sym_line[*]}" ]]; then
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warn "Version disagreement for symbol ${sym}"
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fi
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done < "${TEMPDIR}/Module.symvers"
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fi
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# Read as words, no quotes.
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# shellcheck disable=SC2013
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for i in $(cat "$TEMPDIR/changed_objs")
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@ -868,6 +896,14 @@ mkdir output
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declare -a objnames
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CHANGED=0
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ERROR=0
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# Prepare OOT module symvers file
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if [[ -n "$OOT_MODULE" ]]; then
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BUILDDIR="/lib/modules/$ARCHVERSION/build/"
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cp "$SRCDIR/Module.symvers" "$TEMPDIR/Module.symvers"
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awk '{ print $1 "\t" $2 "\t" $3 "\t" $4}' "${BUILDDIR}/Module.symvers" >> "$TEMPDIR/Module.symvers"
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fi
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for i in $FILES; do
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# In RHEL 7 based kernels, copy_user_64.o misuses the .fixup section,
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# which confuses create-diff-object. It's fine to skip it, it's an
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@ -892,9 +928,6 @@ for i in $FILES; do
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KOBJFILE_PATH="$OOT_MODULE"
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SYMTAB="${TEMPDIR}/module/${KOBJFILE_NAME}.symtab"
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SYMVERS_FILE="$TEMPDIR/Module.symvers"
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BUILDDIR="/lib/modules/$ARCHVERSION/build/"
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cp "$SRCDIR/Module.symvers" "$SYMVERS_FILE"
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awk '{ print $1 "\t" $2 "\t" $3 "\t" $4}' "${BUILDDIR}/Module.symvers" >> "$SYMVERS_FILE"
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else
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KOBJFILE_NAME=$(basename "${KOBJFILE%.ko}")
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KOBJFILE_NAME="${KOBJFILE_NAME//-/_}"
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@ -994,6 +1027,29 @@ if [[ "$USE_KLP" -eq 1 ]]; then
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check_pipe_status create-klp-module
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fi
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if [[ "$CONFIG_MODVERSIONS" -eq 1 ]]; then
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# Check that final module does not reference symbols with different version
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# than the target kernel
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KP_MOD_VALID=true
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# shellcheck disable=SC2086
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while read -ra mod_symbol; do
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if [[ ${#mod_symbol[@]} -lt 2 ]]; then
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continue
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fi
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# Check if the symbol exists in the old Module.symvers, and if it does
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# check that the CRCs are unchanged.
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if ! awk -v sym="${mod_symbol[1]}" -v crc="${mod_symbol[0]}" \
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'$2==sym && $1!=crc { exit 1 }' "$TEMPDIR/Module.symvers"; then
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warn "Patch module references ${mod_symbol[1]} with invalid version"
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KP_MOD_VALID=false
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fi
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done <<< "$(modprobe --dump-modversions $TEMPDIR/patch/$MODNAME.ko)"
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if ! $KP_MOD_VALID; then
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die "Patch module referencing altered exported kernel symbols cannot be loaded"
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fi
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fi
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readelf --wide --symbols "$TEMPDIR/patch/$MODNAME.ko" 2>/dev/null | \
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sed -r 's/\s+\[<localentry>: 8\]//' | \
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awk '($4=="FUNC" || $4=="OBJECT") && ($5=="GLOBAL" || $5=="WEAK") && $7!="UND" {print $NF}' \
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51
test/integration/rhel-7.6/symvers-disagreement-FAIL.patch
Normal file
51
test/integration/rhel-7.6/symvers-disagreement-FAIL.patch
Normal file
@ -0,0 +1,51 @@
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From bcb86fa4e9c31379a9e2716eae29cd53ccca064f Mon Sep 17 00:00:00 2001
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From: Julien Thierry <jthierry@redhat.com>
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Date: Wed, 6 May 2020 14:30:57 +0100
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Subject: [PATCH] Symbol version change
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This change causes:
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1) Some exported symbols in drivers/base/core.c to see their CRCs
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change.
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2) Changes usb_get_dev() referencing a get_device() whose CRC has
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changed, causing the symbol and the new CRC to be included in the
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__version section of the final module.
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This makes the final module unloadable for the target kernel.
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See "Exported symbol versioning" of the patch author guide for more
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detail.
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---
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drivers/base/core.c | 2 ++
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drivers/usb/core/usb.c | 2 ++
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2 files changed, 4 insertions(+)
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diff --git a/drivers/base/core.c b/drivers/base/core.c
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index b9a71137208..4af27e069c2 100644
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--- a/drivers/base/core.c
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+++ b/drivers/base/core.c
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@@ -31,6 +31,8 @@
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#include "base.h"
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#include "power/power.h"
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+#include <linux/blktrace_api.h>
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+
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#ifdef CONFIG_SYSFS_DEPRECATED
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#ifdef CONFIG_SYSFS_DEPRECATED_V2
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long sysfs_deprecated = 1;
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diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
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index f9db3660999..bece0bf4f5a 100644
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--- a/drivers/usb/core/usb.c
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+++ b/drivers/usb/core/usb.c
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@@ -691,6 +691,8 @@ EXPORT_SYMBOL_GPL(usb_alloc_dev);
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*/
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struct usb_device *usb_get_dev(struct usb_device *dev)
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{
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+ barrier();
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+
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if (dev)
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get_device(&dev->dev);
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return dev;
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--
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2.21.1
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51
test/integration/rhel-7.7/symvers-disagreement-FAIL.patch
Normal file
51
test/integration/rhel-7.7/symvers-disagreement-FAIL.patch
Normal file
@ -0,0 +1,51 @@
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From d5513eae5155c6e7e884554d5e3e2c65a7b39cbe Mon Sep 17 00:00:00 2001
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From: Julien Thierry <jthierry@redhat.com>
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Date: Wed, 6 May 2020 14:30:57 +0100
|
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Subject: [PATCH] Symbol version change
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|
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This change causes:
|
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1) Some exported symbols in drivers/base/core.c to see their CRCs
|
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change.
|
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2) Changes usb_get_dev() referencing a get_device() whose CRC has
|
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changed, causing the symbol and the new CRC to be included in the
|
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__version section of the final module.
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|
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This makes the final module unloadable for the target kernel.
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|
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See "Exported symbol versioning" of the patch author guide for more
|
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detail.
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|
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---
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drivers/base/core.c | 2 ++
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drivers/usb/core/usb.c | 2 ++
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2 files changed, 4 insertions(+)
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diff --git a/drivers/base/core.c b/drivers/base/core.c
|
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index b9a71137208..4af27e069c2 100644
|
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--- a/drivers/base/core.c
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+++ b/drivers/base/core.c
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@@ -31,6 +31,8 @@
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#include "base.h"
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#include "power/power.h"
|
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|
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+#include <linux/blktrace_api.h>
|
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+
|
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#ifdef CONFIG_SYSFS_DEPRECATED
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#ifdef CONFIG_SYSFS_DEPRECATED_V2
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long sysfs_deprecated = 1;
|
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diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
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index d6337db2164..0ff9722dfa2 100644
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--- a/drivers/usb/core/usb.c
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+++ b/drivers/usb/core/usb.c
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@@ -693,6 +693,8 @@ EXPORT_SYMBOL_GPL(usb_alloc_dev);
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*/
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struct usb_device *usb_get_dev(struct usb_device *dev)
|
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{
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+ barrier();
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+
|
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if (dev)
|
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get_device(&dev->dev);
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return dev;
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--
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2.21.3
|
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|
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49
test/integration/rhel-7.8/symvers-disagreement-FAIL.patch
Normal file
49
test/integration/rhel-7.8/symvers-disagreement-FAIL.patch
Normal file
@ -0,0 +1,49 @@
|
||||
From da109d66a890373d0aa831f97b49aaffcc4eeb45 Mon Sep 17 00:00:00 2001
|
||||
From: Julien Thierry <jthierry@redhat.com>
|
||||
Date: Wed, 6 May 2020 14:30:57 +0100
|
||||
Subject: [PATCH] Symbol version change
|
||||
|
||||
This change causes:
|
||||
1) Some exported symbols in drivers/base/core.c to see their CRCs
|
||||
change.
|
||||
2) Changes a function referencing a function whose CRC has changed,
|
||||
causing the symbol and the new CRC to be included in the __version
|
||||
section of the final module.
|
||||
|
||||
See "Exported symbol versioning" of the patch author guide for more
|
||||
detail.
|
||||
|
||||
---
|
||||
drivers/base/core.c | 2 ++
|
||||
drivers/usb/core/usb.c | 2 ++
|
||||
2 files changed, 4 insertions(+)
|
||||
|
||||
diff --git a/drivers/base/core.c b/drivers/base/core.c
|
||||
index b9a71137208..4af27e069c2 100644
|
||||
--- a/drivers/base/core.c
|
||||
+++ b/drivers/base/core.c
|
||||
@@ -31,6 +31,8 @@
|
||||
#include "base.h"
|
||||
#include "power/power.h"
|
||||
|
||||
+#include <linux/blktrace_api.h>
|
||||
+
|
||||
#ifdef CONFIG_SYSFS_DEPRECATED
|
||||
#ifdef CONFIG_SYSFS_DEPRECATED_V2
|
||||
long sysfs_deprecated = 1;
|
||||
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
|
||||
index 8b1c4a5ee78..1b7997b58c0 100644
|
||||
--- a/drivers/usb/core/usb.c
|
||||
+++ b/drivers/usb/core/usb.c
|
||||
@@ -693,6 +693,8 @@ EXPORT_SYMBOL_GPL(usb_alloc_dev);
|
||||
*/
|
||||
struct usb_device *usb_get_dev(struct usb_device *dev)
|
||||
{
|
||||
+ barrier();
|
||||
+
|
||||
if (dev)
|
||||
get_device(&dev->dev);
|
||||
return dev;
|
||||
--
|
||||
2.21.3
|
||||
|
||||
51
test/integration/rhel-8.0/symvers-disagreement-FAIL.patch
Normal file
51
test/integration/rhel-8.0/symvers-disagreement-FAIL.patch
Normal file
@ -0,0 +1,51 @@
|
||||
From 7085a655b8d665b6314e8dab2f803bac0aea04ec Mon Sep 17 00:00:00 2001
|
||||
From: Julien Thierry <jthierry@redhat.com>
|
||||
Date: Wed, 6 May 2020 14:30:57 +0100
|
||||
Subject: [PATCH] Symbol version change
|
||||
|
||||
This change causes:
|
||||
1) Some exported symbols in drivers/base/core.c to see their CRCs
|
||||
change.
|
||||
2) Changes usb_get_dev() referencing a get_device() whose CRC has
|
||||
changed, causing the symbol and the new CRC to be included in the
|
||||
__version section of the final module.
|
||||
|
||||
This makes the final module unloadable for the target kernel.
|
||||
|
||||
See "Exported symbol versioning" of the patch author guide for more
|
||||
detail.
|
||||
|
||||
---
|
||||
drivers/base/core.c | 2 ++
|
||||
drivers/usb/core/usb.c | 2 ++
|
||||
2 files changed, 4 insertions(+)
|
||||
|
||||
diff --git a/drivers/base/core.c b/drivers/base/core.c
|
||||
index df3e1a44707a..15c9d6e2e1e0 100644
|
||||
--- a/drivers/base/core.c
|
||||
+++ b/drivers/base/core.c
|
||||
@@ -29,6 +29,8 @@
|
||||
#include "base.h"
|
||||
#include "power/power.h"
|
||||
|
||||
+#include <linux/blktrace_api.h>
|
||||
+
|
||||
#ifdef CONFIG_SYSFS_DEPRECATED
|
||||
#ifdef CONFIG_SYSFS_DEPRECATED_V2
|
||||
long sysfs_deprecated = 1;
|
||||
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
|
||||
index 623be3174fb3..4ddd74ae0bb9 100644
|
||||
--- a/drivers/usb/core/usb.c
|
||||
+++ b/drivers/usb/core/usb.c
|
||||
@@ -685,6 +685,8 @@ EXPORT_SYMBOL_GPL(usb_alloc_dev);
|
||||
*/
|
||||
struct usb_device *usb_get_dev(struct usb_device *dev)
|
||||
{
|
||||
+ barrier();
|
||||
+
|
||||
if (dev)
|
||||
get_device(&dev->dev);
|
||||
return dev;
|
||||
--
|
||||
2.21.3
|
||||
|
||||
51
test/integration/rhel-8.1/symvers-disagreement-FAIL.patch
Normal file
51
test/integration/rhel-8.1/symvers-disagreement-FAIL.patch
Normal file
@ -0,0 +1,51 @@
|
||||
From c63702554e54b992793fe3598ea8c8c415bef908 Mon Sep 17 00:00:00 2001
|
||||
From: Julien Thierry <jthierry@redhat.com>
|
||||
Date: Wed, 6 May 2020 14:30:57 +0100
|
||||
Subject: [PATCH] Symbol version change
|
||||
|
||||
This change causes:
|
||||
1) Some exported symbols in drivers/base/core.c to see their CRCs
|
||||
change.
|
||||
2) Changes usb_get_dev() referencing a get_device() whose CRC has
|
||||
changed, causing the symbol and the new CRC to be included in the
|
||||
__version section of the final module.
|
||||
|
||||
This makes the final module unloadable for the target kernel.
|
||||
|
||||
See "Exported symbol versioning" of the patch author guide for more
|
||||
detail.
|
||||
|
||||
---
|
||||
drivers/base/core.c | 2 ++
|
||||
drivers/usb/core/usb.c | 2 ++
|
||||
2 files changed, 4 insertions(+)
|
||||
|
||||
diff --git a/drivers/base/core.c b/drivers/base/core.c
|
||||
index 2ab316d85651..2ef19920f6ab 100644
|
||||
--- a/drivers/base/core.c
|
||||
+++ b/drivers/base/core.c
|
||||
@@ -29,6 +29,8 @@
|
||||
#include "base.h"
|
||||
#include "power/power.h"
|
||||
|
||||
+#include <linux/blktrace_api.h>
|
||||
+
|
||||
#ifdef CONFIG_SYSFS_DEPRECATED
|
||||
#ifdef CONFIG_SYSFS_DEPRECATED_V2
|
||||
long sysfs_deprecated = 1;
|
||||
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
|
||||
index 0a2b261a27c9..51a1868c9cea 100644
|
||||
--- a/drivers/usb/core/usb.c
|
||||
+++ b/drivers/usb/core/usb.c
|
||||
@@ -685,6 +685,8 @@ EXPORT_SYMBOL_GPL(usb_alloc_dev);
|
||||
*/
|
||||
struct usb_device *usb_get_dev(struct usb_device *dev)
|
||||
{
|
||||
+ barrier();
|
||||
+
|
||||
if (dev)
|
||||
get_device(&dev->dev);
|
||||
return dev;
|
||||
--
|
||||
2.21.3
|
||||
|
||||
51
test/integration/rhel-8.2/symvers-disagreement-FAIL.patch
Normal file
51
test/integration/rhel-8.2/symvers-disagreement-FAIL.patch
Normal file
@ -0,0 +1,51 @@
|
||||
From 2d6b7bce089e52563bd9c67df62f48e90b48047d Mon Sep 17 00:00:00 2001
|
||||
From: Julien Thierry <jthierry@redhat.com>
|
||||
Date: Wed, 6 May 2020 14:30:57 +0100
|
||||
Subject: [PATCH] Symbol version change
|
||||
|
||||
This change causes:
|
||||
1) Some exported symbols in drivers/base/core.c to see their CRCs
|
||||
change.
|
||||
2) Changes usb_get_dev() referencing a get_device() whose CRC has
|
||||
changed, causing the symbol and the new CRC to be included in the
|
||||
__version section of the final module.
|
||||
|
||||
This makes the final module unloadable for the target kernel.
|
||||
|
||||
See "Exported symbol versioning" of the patch author guide for more
|
||||
detail.
|
||||
|
||||
---
|
||||
drivers/base/core.c | 2 ++
|
||||
drivers/usb/core/usb.c | 2 ++
|
||||
2 files changed, 4 insertions(+)
|
||||
|
||||
diff --git a/drivers/base/core.c b/drivers/base/core.c
|
||||
index 26bae20f0553..506ebbf0a210 100644
|
||||
--- a/drivers/base/core.c
|
||||
+++ b/drivers/base/core.c
|
||||
@@ -30,6 +30,8 @@
|
||||
#include "base.h"
|
||||
#include "power/power.h"
|
||||
|
||||
+#include <linux/blktrace_api.h>
|
||||
+
|
||||
#ifdef CONFIG_SYSFS_DEPRECATED
|
||||
#ifdef CONFIG_SYSFS_DEPRECATED_V2
|
||||
long sysfs_deprecated = 1;
|
||||
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
|
||||
index f74e6bda1788..86f7d453549c 100644
|
||||
--- a/drivers/usb/core/usb.c
|
||||
+++ b/drivers/usb/core/usb.c
|
||||
@@ -685,6 +685,8 @@ EXPORT_SYMBOL_GPL(usb_alloc_dev);
|
||||
*/
|
||||
struct usb_device *usb_get_dev(struct usb_device *dev)
|
||||
{
|
||||
+ barrier();
|
||||
+
|
||||
if (dev)
|
||||
get_device(&dev->dev);
|
||||
return dev;
|
||||
--
|
||||
2.21.3
|
||||
|
||||
Loading…
Reference in New Issue
Block a user