Re: [PATCH 24/43] kmsan: disable KMSAN instrumentation for certain kernel parts

[Mark Rutland <mark.rutland@arm.com>]

On Tue, Dec 14, 2021 at 05:20:31PM +0100, Alexander Potapenko wrote:
> Instrumenting some files with KMSAN will result in kernel being unable
> to link, boot or crashing at runtime for various reasons (e.g. infinite
> recursion caused by instrumentation hooks calling instrumented code again).
> 
> Completely omit KMSAN instrumentation in the following places:
>  - arch/x86/boot and arch/x86/realmode/rm, as KMSAN doesn't work for i386;
>  - arch/x86/entry/vdso, which isn't linked with KMSAN runtime;
>  - three files in arch/x86/kernel - boot problems;
>  - arch/x86/mm/cpu_entry_area.c - recursion;
>  - EFI stub - build failures;
>  - kcov, stackdepot, lockdep - recursion.

It probably makes sense to split the arch/x86/ bits from everything else, and
to group the arch/x86 enablement patches together closer to the end of the
series.

The non-x86 changes all look fine to me.

Mark.

> 
> Signed-off-by: Alexander Potapenko <glider@google.com>
> ---
> Link: https://linux-review.googlesource.com/id/Id5e5c4a9f9d53c24a35ebb633b814c414628d81b
> ---
>  arch/x86/boot/Makefile                | 1 +
>  arch/x86/boot/compressed/Makefile     | 1 +
>  arch/x86/entry/vdso/Makefile          | 3 +++
>  arch/x86/kernel/Makefile              | 2 ++
>  arch/x86/kernel/cpu/Makefile          | 1 +
>  arch/x86/mm/Makefile                  | 2 ++
>  arch/x86/realmode/rm/Makefile         | 1 +
>  drivers/firmware/efi/libstub/Makefile | 1 +
>  kernel/Makefile                       | 1 +
>  kernel/locking/Makefile               | 3 ++-
>  lib/Makefile                          | 1 +
>  11 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
> index b5aecb524a8aa..d5623232b763f 100644
> --- a/arch/x86/boot/Makefile
> +++ b/arch/x86/boot/Makefile
> @@ -12,6 +12,7 @@
>  # Sanitizer runtimes are unavailable and cannot be linked for early boot code.
>  KASAN_SANITIZE			:= n
>  KCSAN_SANITIZE			:= n
> +KMSAN_SANITIZE			:= n
>  OBJECT_FILES_NON_STANDARD	:= y
>  
>  # Kernel does not boot with kcov instrumentation here.
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 431bf7f846c3c..c4a284b738e71 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -20,6 +20,7 @@
>  # Sanitizer runtimes are unavailable and cannot be linked for early boot code.
>  KASAN_SANITIZE			:= n
>  KCSAN_SANITIZE			:= n
> +KMSAN_SANITIZE			:= n
>  OBJECT_FILES_NON_STANDARD	:= y
>  
>  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> index a2dddcc189f69..f2a175d872b07 100644
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -11,6 +11,9 @@ include $(srctree)/lib/vdso/Makefile
>  
>  # Sanitizer runtimes are unavailable and cannot be linked here.
>  KASAN_SANITIZE			:= n
> +KMSAN_SANITIZE_vclock_gettime.o := n
> +KMSAN_SANITIZE_vgetcpu.o	:= n
> +
>  UBSAN_SANITIZE			:= n
>  KCSAN_SANITIZE			:= n
>  OBJECT_FILES_NON_STANDARD	:= y
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 2ff3e600f4269..0b9fc3ecce2de 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -35,6 +35,8 @@ KASAN_SANITIZE_cc_platform.o				:= n
>  # With some compiler versions the generated code results in boot hangs, caused
>  # by several compilation units. To be safe, disable all instrumentation.
>  KCSAN_SANITIZE := n
> +KMSAN_SANITIZE_head$(BITS).o				:= n
> +KMSAN_SANITIZE_nmi.o					:= n
>  
>  OBJECT_FILES_NON_STANDARD_test_nx.o			:= y
>  
> diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
> index 9661e3e802be5..f10a921ee7565 100644
> --- a/arch/x86/kernel/cpu/Makefile
> +++ b/arch/x86/kernel/cpu/Makefile
> @@ -12,6 +12,7 @@ endif
>  # If these files are instrumented, boot hangs during the first second.
>  KCOV_INSTRUMENT_common.o := n
>  KCOV_INSTRUMENT_perf_event.o := n
> +KMSAN_SANITIZE_common.o := n
>  
>  # As above, instrumenting secondary CPU boot code causes boot hangs.
>  KCSAN_SANITIZE_common.o := n
> diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
> index 5864219221ca8..747d4630d52ce 100644
> --- a/arch/x86/mm/Makefile
> +++ b/arch/x86/mm/Makefile
> @@ -10,6 +10,8 @@ KASAN_SANITIZE_mem_encrypt_identity.o	:= n
>  # Disable KCSAN entirely, because otherwise we get warnings that some functions
>  # reference __initdata sections.
>  KCSAN_SANITIZE := n
> +# Avoid recursion by not calling KMSAN hooks for CEA code.
> +KMSAN_SANITIZE_cpu_entry_area.o := n
>  
>  ifdef CONFIG_FUNCTION_TRACER
>  CFLAGS_REMOVE_mem_encrypt.o		= -pg
> diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
> index 83f1b6a56449f..f614009d3e4e2 100644
> --- a/arch/x86/realmode/rm/Makefile
> +++ b/arch/x86/realmode/rm/Makefile
> @@ -10,6 +10,7 @@
>  # Sanitizer runtimes are unavailable and cannot be linked here.
>  KASAN_SANITIZE			:= n
>  KCSAN_SANITIZE			:= n
> +KMSAN_SANITIZE			:= n
>  OBJECT_FILES_NON_STANDARD	:= y
>  
>  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index d0537573501e9..81432d0c904b1 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -46,6 +46,7 @@ GCOV_PROFILE			:= n
>  # Sanitizer runtimes are unavailable and cannot be linked here.
>  KASAN_SANITIZE			:= n
>  KCSAN_SANITIZE			:= n
> +KMSAN_SANITIZE			:= n
>  UBSAN_SANITIZE			:= n
>  OBJECT_FILES_NON_STANDARD	:= y
>  
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 186c49582f45b..e5dd600e63d8a 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -39,6 +39,7 @@ KCOV_INSTRUMENT_kcov.o := n
>  KASAN_SANITIZE_kcov.o := n
>  KCSAN_SANITIZE_kcov.o := n
>  UBSAN_SANITIZE_kcov.o := n
> +KMSAN_SANITIZE_kcov.o := n
>  CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack) -fno-stack-protector
>  
>  # Don't instrument error handlers
> diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile
> index d51cabf28f382..ea925731fa40f 100644
> --- a/kernel/locking/Makefile
> +++ b/kernel/locking/Makefile
> @@ -5,8 +5,9 @@ KCOV_INSTRUMENT		:= n
>  
>  obj-y += mutex.o semaphore.o rwsem.o percpu-rwsem.o
>  
> -# Avoid recursion lockdep -> KCSAN -> ... -> lockdep.
> +# Avoid recursion lockdep -> sanitizer -> ... -> lockdep.
>  KCSAN_SANITIZE_lockdep.o := n
> +KMSAN_SANITIZE_lockdep.o := n
>  
>  ifdef CONFIG_FUNCTION_TRACER
>  CFLAGS_REMOVE_lockdep.o = $(CC_FLAGS_FTRACE)
> diff --git a/lib/Makefile b/lib/Makefile
> index 364c23f155781..8e5ae9d5966de 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -268,6 +268,7 @@ obj-$(CONFIG_IRQ_POLL) += irq_poll.o
>  CFLAGS_stackdepot.o += -fno-builtin
>  obj-$(CONFIG_STACKDEPOT) += stackdepot.o
>  KASAN_SANITIZE_stackdepot.o := n
> +KMSAN_SANITIZE_stackdepot.o := n
>  KCOV_INSTRUMENT_stackdepot.o := n
>  
>  libfdt_files = fdt.o fdt_ro.o fdt_wip.o fdt_rw.o fdt_sw.o fdt_strerror.o \
> -- 
> 2.34.1.173.g76aa8bc2d0-goog
>