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917e3ad332
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: 0d345996e4 ("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
62 lines
1.9 KiB
Makefile
62 lines
1.9 KiB
Makefile
# SPDX-License-Identifier: GPL-2.0
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# Kernel does not boot with instrumentation of tlb.c and mem_encrypt*.c
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KCOV_INSTRUMENT_tlb.o := n
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KCOV_INSTRUMENT_mem_encrypt.o := n
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KCOV_INSTRUMENT_mem_encrypt_amd.o := n
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KCOV_INSTRUMENT_pgprot.o := n
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# See the "Disable KCOV" comment in arch/x86/kernel/Makefile.
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KCOV_INSTRUMENT_physaddr.o := n
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KASAN_SANITIZE_mem_encrypt.o := n
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KASAN_SANITIZE_mem_encrypt_amd.o := n
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KASAN_SANITIZE_pgprot.o := n
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# Disable KCSAN entirely, because otherwise we get warnings that some functions
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# reference __initdata sections.
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KCSAN_SANITIZE := n
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# Avoid recursion by not calling KMSAN hooks for CEA code.
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KMSAN_SANITIZE_cpu_entry_area.o := n
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ifdef CONFIG_FUNCTION_TRACER
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CFLAGS_REMOVE_mem_encrypt.o = -pg
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CFLAGS_REMOVE_mem_encrypt_amd.o = -pg
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CFLAGS_REMOVE_pgprot.o = -pg
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endif
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obj-y := init.o init_$(BITS).o fault.o ioremap.o extable.o mmap.o \
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pgtable.o physaddr.o tlb.o cpu_entry_area.o maccess.o pgprot.o
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obj-y += pat/
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# Make sure __phys_addr has no stackprotector
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CFLAGS_physaddr.o := -fno-stack-protector
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obj-$(CONFIG_X86_32) += pgtable_32.o iomap_32.o
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obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
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obj-$(CONFIG_PTDUMP) += dump_pagetables.o
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obj-$(CONFIG_PTDUMP_DEBUGFS) += debug_pagetables.o
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KASAN_SANITIZE_kasan_init_$(BITS).o := n
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obj-$(CONFIG_KASAN) += kasan_init_$(BITS).o
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KMSAN_SANITIZE_kmsan_shadow.o := n
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obj-$(CONFIG_KMSAN) += kmsan_shadow.o
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obj-$(CONFIG_MMIOTRACE) += mmiotrace.o
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mmiotrace-y := kmmio.o pf_in.o mmio-mod.o
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obj-$(CONFIG_MMIOTRACE_TEST) += testmmiotrace.o
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obj-$(CONFIG_NUMA) += numa.o
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obj-$(CONFIG_AMD_NUMA) += amdtopology.o
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obj-$(CONFIG_ACPI_NUMA) += srat.o
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obj-$(CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS) += pkeys.o
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obj-$(CONFIG_RANDOMIZE_MEMORY) += kaslr.o
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obj-$(CONFIG_MITIGATION_PAGE_TABLE_ISOLATION) += pti.o
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obj-$(CONFIG_X86_MEM_ENCRYPT) += mem_encrypt.o
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obj-$(CONFIG_AMD_MEM_ENCRYPT) += mem_encrypt_amd.o
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obj-$(CONFIG_AMD_MEM_ENCRYPT) += mem_encrypt_boot.o
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