From: Aleksandr Nogikh <nogikh@google.com> stable inclusion from stable-v6.12.93 commit 593d67032544b9271094fc9b43e437e017cb2b2f category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/14889 CVE: CVE-2026-43331 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit 917e3ad3321e75ca0223d5ccf26ceda116aa51e1 ] The load_segments() function changes segment registers, invalidating GS base (which KCOV relies on for per-cpu data). When CONFIG_KCOV is enabled, any subsequent instrumented C code call (e.g. native_gdt_invalidate()) begins crashing the kernel in an endless loop. To reproduce the problem, it's sufficient to do kexec on a KCOV-instrumented kernel: $ kexec -l /boot/otherKernel $ kexec -e The real-world context for this problem is enabling crash dump collection in syzkaller. For this, the tool loads a panic kernel before fuzzing and then calls makedumpfile after the panic. This workflow requires both CONFIG_KEXEC and CONFIG_KCOV to be enabled simultaneously. Adding safeguards directly to the KCOV fast-path (__sanitizer_cov_trace_pc()) is also undesirable as it would introduce an extra performance overhead. Disabling instrumentation for the individual functions would be too fragile, so disable KCOV instrumentation for the entire machine_kexec_64.c and physaddr.c. If coverage-guided fuzzing ever needs these components in the future, other approaches should be considered. The problem is not relevant for 32 bit kernels as CONFIG_KCOV is not supported there. [ bp: Space out comment for better readability. ] Fixes: 0d345996e4cb ("x86/kernel: increase kcov coverage under arch/x86/kernel folder") Signed-off-by: Aleksandr Nogikh <nogikh@google.com> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Reviewed-by: Dmitry Vyukov <dvyukov@google.com> Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260325154825.551191-1-nogikh@google.com Signed-off-by: Sasha Levin <sashal@kernel.org> Conflicts: arch/x86/kernel/Makefile [context conflict.] Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com> --- arch/x86/kernel/Makefile | 14 ++++++++++++++ arch/x86/mm/Makefile | 2 ++ 2 files changed, 16 insertions(+) diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile index 341422135d9d..767bbcfd4dc3 100644 --- a/arch/x86/kernel/Makefile +++ b/arch/x86/kernel/Makefile @@ -39,6 +39,20 @@ KMSAN_SANITIZE_nmi.o := n KCOV_INSTRUMENT_head$(BITS).o := n KCOV_INSTRUMENT_sev.o := n +# Disable KCOV to prevent crashes during kexec: load_segments() invalidates +# the GS base, which KCOV relies on for per-CPU data. +# +# As KCOV and KEXEC compatibility should be preserved (e.g. syzkaller is +# using it to collect crash dumps during kernel fuzzing), disabling +# KCOV for KEXEC kernels is not an option. Selectively disabling KCOV +# instrumentation for individual affected functions can be fragile, while +# adding more checks to KCOV would slow it down. +# +# As a compromise solution, disable KCOV instrumentation for the whole +# source code file. If its coverage is ever needed, other approaches +# should be considered. +KCOV_INSTRUMENT_machine_kexec_64.o := n + CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace obj-y += head_$(BITS).o diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile index c9d9bee63d7d..d8f01c0f717b 100644 --- a/arch/x86/mm/Makefile +++ b/arch/x86/mm/Makefile @@ -5,6 +5,8 @@ KCOV_INSTRUMENT_mem_encrypt.o := n KCOV_INSTRUMENT_mem_encrypt_amd.o := n KCOV_INSTRUMENT_mem_encrypt_identity.o := n KCOV_INSTRUMENT_pgprot.o := n +# See the "Disable KCOV" comment in arch/x86/kernel/Makefile. +KCOV_INSTRUMENT_physaddr.o := n KASAN_SANITIZE_mem_encrypt.o := n KASAN_SANITIZE_mem_encrypt_amd.o := n -- 2.34.1