From: Konstantin Khorenko <khorenko@virtuozzo.com> mainline inclusion from mainline-v7.2-rc1 commit 56cb9b7d96b28a1173a510ab25354b6599ad3a33 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/16154 CVE: CVE-2026-63825 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... ---------------------------------------------------------------------- GCC's GCOV instrumentation can merge global branch counters with loop induction variables as an optimization. In inflate_fast(), the inner copy loops get transformed so that the GCOV counter value is loaded multiple times to compute the loop base address, start index, and end bound. Since GCOV counters are global (not per-CPU), concurrent execution on different CPUs causes the counter to change between loads, producing inconsistent values and out-of-bounds memory writes. The crash manifests during IPComp (IP Payload Compression) processing when inflate_fast() runs concurrently on multiple CPUs: BUG: unable to handle page fault for address: ffffd0a3c0902ffa RIP: inflate_fast+1431 Call Trace: zlib_inflate __deflate_decompress crypto_comp_decompress ipcomp_decompress [xfrm_ipcomp] ipcomp_input [xfrm_ipcomp] xfrm_input At the crash point, the compiler generated three loads from the same global GCOV counter (__gcov0.inflate_fast+216) to compute base, start, and end for an indexed loop. Another CPU modified the counter between loads, making the values inconsistent - the write went 3.4 MB past a 65 KB buffer. Add -fprofile-update=prefer-atomic to CFLAGS_GCOV at the global level in the top-level Makefile, guarded by a try-run compile test. The test compiles a minimal program with and without -fprofile-update=prefer-atomic using the full KBUILD_CFLAGS, then compares undefined symbols in the resulting object files. If prefer-atomic introduces new undefined references (such as __atomic_fetch_add_8 on i386 or __aarch64_ldadd8_relax on arm64 with outline-atomics), the flag is not added -- the kernel does not link against libatomic. On architectures where GCC inlines 64-bit atomic counter updates (x86_64, s390, ...) the test passes and the flag is enabled, preventing the compiler from merging counters with loop induction variables and fixing the observed concurrent-access crash. On architectures where the flag would introduce libatomic dependencies, it is silently omitted and behaviour is no worse than before this patch. Move the CFLAGS_GCOV block from its original position (before the arch Makefile include) to after the core KBUILD_CFLAGS assignments but before the scripts/Makefile.gcc-plugins include. This placement ensures the try-run test sees arch-specific flags (-m32, -march=, -mno-outline-atomics) while avoiding GCC plugin flags (-fplugin=) that would break the test on clean builds when plugin shared objects do not yet exist. Link: https://lore.kernel.org/20260511105052.417187-2-khorenko@virtuozzo.com Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com> Tested-by: Arnd Bergmann <arnd@arndb.de> Tested-by: Peter Oberparleiter <oberpar@linux.ibm.com> Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com> Cc: Masahiro Yamada <masahiroy@kernel.org> Cc: Miguel Ojeda <ojeda@kernel.org> Cc: Mikhail Zaslonko <zaslonko@linux.ibm.com> Cc: Nathan Chancellor <nathan@kernel.org> Cc: Pavel Tikhomirov <ptikhomirov@virtuozzo.com> Cc: Thomas Weißschuh <linux@weissschuh.net> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Conflicts: Makefile [Fix ctx diff.] Signed-off-by: Luo Gengkun <luogengkun2@huawei.com> --- Makefile | 27 +++++++++++++++++++++------ 1 file changed, 21 insertions(+), 6 deletions(-) diff --git a/Makefile b/Makefile index 2920c35a0831..bd7e86c16447 100644 --- a/Makefile +++ b/Makefile @@ -753,12 +753,6 @@ all: vmlinux CFLAGS_PGO_CLANG := -fprofile-generate export CFLAGS_PGO_CLANG -CFLAGS_GCOV := -fprofile-arcs -ftest-coverage -ifdef CONFIG_CC_IS_GCC -CFLAGS_GCOV += -fno-tree-loop-im -endif -export CFLAGS_GCOV - # The arch Makefiles can override CC_FLAGS_FTRACE. We may also append it later. ifdef CONFIG_FUNCTION_TRACER CC_FLAGS_FTRACE := -pg @@ -1006,6 +1000,27 @@ endif # Ensure compilers do not transform certain loops into calls to wcslen() KBUILD_CFLAGS += -fno-builtin-wcslen +CFLAGS_GCOV := -fprofile-arcs -ftest-coverage +ifdef CONFIG_CC_IS_GCC +CFLAGS_GCOV += -fno-tree-loop-im +# Use atomic counter updates to avoid concurrent-access crashes in GCOV. +# Only enable if -fprofile-update=prefer-atomic does not introduce new +# undefined symbols (e.g. libatomic calls that the kernel cannot link). +CFLAGS_GCOV += $(call try-run,\ + echo 'long long x; void f(void){x++;}' | \ + $(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -w -fprofile-arcs \ + -ftest-coverage -x c - -c -o "$$TMP.base" && \ + echo 'long long x; void f(void){x++;}' | \ + $(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -w -fprofile-arcs \ + -ftest-coverage -fprofile-update=prefer-atomic \ + -x c - -c -o "$$TMP" && \ + $(NM) "$$TMP.base" | grep ' U ' > "$$TMP.ubase" || true ; \ + $(NM) "$$TMP" | grep ' U ' > "$$TMP.utest" || true ; \ + cmp -s "$$TMP.ubase" "$$TMP.utest",\ + -fprofile-update=prefer-atomic) +endif +export CFLAGS_GCOV + # change __FILE__ to the relative path from the srctree KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) -- 2.34.1