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Date:   Wed, 27 Apr 2022 16:09:51 +0200
From:   Marco Elver <elver@google.com>
To:     Alexander Potapenko <glider@google.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Christoph Hellwig <hch@lst.de>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kees Cook <keescook@chromium.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Pekka Enberg <penberg@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>, kasan-dev@googlegroups.com,
        linux-mm@kvack.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 12/46] kmsan: add KMSAN runtime core
Message-ID: <YmlOrxYCbAnVrV7r@elver.google.com>
References: <20220426164315.625149-1-glider@google.com>
 <20220426164315.625149-13-glider@google.com>
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On Tue, Apr 26, 2022 at 06:42PM +0200, Alexander Potapenko wrote:
> For each memory location KernelMemorySanitizer maintains two types of
> metadata:
> 1. The so-called shadow of that location - а byte:byte mapping describing
>    whether or not individual bits of memory are initialized (shadow is 0)
>    or not (shadow is 1).
> 2. The origins of that location - а 4-byte:4-byte mapping containing
>    4-byte IDs of the stack traces where uninitialized values were
>    created.
> 
> Each struct page now contains pointers to two struct pages holding
> KMSAN metadata (shadow and origins) for the original struct page.
> Utility routines in mm/kmsan/core.c and mm/kmsan/shadow.c handle the
> metadata creation, addressing, copying and checking.
> mm/kmsan/report.c performs error reporting in the cases an uninitialized
> value is used in a way that leads to undefined behavior.
> 
> KMSAN compiler instrumentation is responsible for tracking the metadata
> along with the kernel memory. mm/kmsan/instrumentation.c provides the
> implementation for instrumentation hooks that are called from files
> compiled with -fsanitize=kernel-memory.
> 
> To aid parameter passing (also done at instrumentation level), each
> task_struct now contains a struct kmsan_task_state used to track the
> metadata of function parameters and return values for that task.
> 
> Finally, this patch provides CONFIG_KMSAN that enables KMSAN, and
> declares CFLAGS_KMSAN, which are applied to files compiled with KMSAN.
> The KMSAN_SANITIZE:=n Makefile directive can be used to completely
> disable KMSAN instrumentation for certain files.
> 
> Similarly, KMSAN_ENABLE_CHECKS:=n disables KMSAN checks and makes newly
> created stack memory initialized.
> 
> Users can also use functions from include/linux/kmsan-checks.h to mark
> certain memory regions as uninitialized or initialized (this is called
> "poisoning" and "unpoisoning") or check that a particular region is
> initialized.
> 
> Signed-off-by: Alexander Potapenko <glider@google.com>
> ---
> v2:
>  -- as requested by Greg K-H, moved hooks for different subsystems to respective patches,
>     rewrote the patch description;
>  -- addressed comments by Dmitry Vyukov;
>  -- added a note about KMSAN being not intended for production use.
>  -- fix case of unaligned dst in kmsan_internal_memmove_metadata()
> 
> v3:
>  -- print build IDs in reports where applicable
>  -- drop redundant filter_irq_stacks(), unpoison the local passed to __stack_depot_save()
>  -- remove a stray BUG()
> 
> Link: https://linux-review.googlesource.com/id/I9b71bfe3425466c97159f9de0062e5e8e4fec866
> ---
>  Makefile                     |   1 +
>  include/linux/kmsan-checks.h |  64 +++++
>  include/linux/kmsan.h        |  47 ++++
>  include/linux/mm_types.h     |  12 +
>  include/linux/sched.h        |   5 +
>  lib/Kconfig.debug            |   1 +
>  lib/Kconfig.kmsan            |  23 ++
>  mm/Makefile                  |   1 +
>  mm/kmsan/Makefile            |  18 ++
>  mm/kmsan/core.c              | 458 +++++++++++++++++++++++++++++++++++
>  mm/kmsan/hooks.c             |  66 +++++
>  mm/kmsan/instrumentation.c   | 267 ++++++++++++++++++++
>  mm/kmsan/kmsan.h             | 183 ++++++++++++++
>  mm/kmsan/report.c            | 211 ++++++++++++++++
>  mm/kmsan/shadow.c            | 186 ++++++++++++++
>  scripts/Makefile.kmsan       |   1 +
>  scripts/Makefile.lib         |   9 +
>  17 files changed, 1553 insertions(+)
>  create mode 100644 include/linux/kmsan-checks.h
>  create mode 100644 include/linux/kmsan.h
>  create mode 100644 lib/Kconfig.kmsan
>  create mode 100644 mm/kmsan/Makefile
>  create mode 100644 mm/kmsan/core.c
>  create mode 100644 mm/kmsan/hooks.c
>  create mode 100644 mm/kmsan/instrumentation.c
>  create mode 100644 mm/kmsan/kmsan.h
>  create mode 100644 mm/kmsan/report.c
>  create mode 100644 mm/kmsan/shadow.c
>  create mode 100644 scripts/Makefile.kmsan
> 
> diff --git a/Makefile b/Makefile
> index c3ec1ea423797..d3c7dcd9f0fea 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1009,6 +1009,7 @@ include-y			:= scripts/Makefile.extrawarn
>  include-$(CONFIG_DEBUG_INFO)	+= scripts/Makefile.debug
>  include-$(CONFIG_KASAN)		+= scripts/Makefile.kasan
>  include-$(CONFIG_KCSAN)		+= scripts/Makefile.kcsan
> +include-$(CONFIG_KMSAN)		+= scripts/Makefile.kmsan
>  include-$(CONFIG_UBSAN)		+= scripts/Makefile.ubsan
>  include-$(CONFIG_KCOV)		+= scripts/Makefile.kcov
>  include-$(CONFIG_GCC_PLUGINS)	+= scripts/Makefile.gcc-plugins
> diff --git a/include/linux/kmsan-checks.h b/include/linux/kmsan-checks.h
> new file mode 100644
> index 0000000000000..a6522a0c28df9
> --- /dev/null
> +++ b/include/linux/kmsan-checks.h
> @@ -0,0 +1,64 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * KMSAN checks to be used for one-off annotations in subsystems.
> + *
> + * Copyright (C) 2017-2022 Google LLC
> + * Author: Alexander Potapenko <glider@google.com>
> + *
> + */
> +
> +#ifndef _LINUX_KMSAN_CHECKS_H
> +#define _LINUX_KMSAN_CHECKS_H
> +
> +#include <linux/types.h>
> +
> +#ifdef CONFIG_KMSAN
> +
> +/**
> + * kmsan_poison_memory() - Mark the memory range as uninitialized.
> + * @address: address to start with.
> + * @size:    size of buffer to poison.
> + * @flags:   GFP flags for allocations done by this function.
> + *
> + * Until other data is written to this range, KMSAN will treat it as
> + * uninitialized. Error reports for this memory will reference the call site of
> + * kmsan_poison_memory() as origin.
> + */
> +void kmsan_poison_memory(const void *address, size_t size, gfp_t flags);
> +
> +/**
> + * kmsan_unpoison_memory() -  Mark the memory range as initialized.
> + * @address: address to start with.
> + * @size:    size of buffer to unpoison.
> + *
> + * Until other data is written to this range, KMSAN will treat it as
> + * initialized.
> + */
> +void kmsan_unpoison_memory(const void *address, size_t size);
> +
> +/**
> + * kmsan_check_memory() - Check the memory range for being initialized.
> + * @address: address to start with.
> + * @size:    size of buffer to check.
> + *
> + * If any piece of the given range is marked as uninitialized, KMSAN will report
> + * an error.
> + */
> +void kmsan_check_memory(const void *address, size_t size);
> +
> +#else
> +
> +static inline void kmsan_poison_memory(const void *address, size_t size,
> +				       gfp_t flags)
> +{
> +}
> +static inline void kmsan_unpoison_memory(const void *address, size_t size)
> +{
> +}
> +static inline void kmsan_check_memory(const void *address, size_t size)
> +{
> +}
> +
> +#endif
> +
> +#endif /* _LINUX_KMSAN_CHECKS_H */
> diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h
> new file mode 100644
> index 0000000000000..4e35f43eceaa9
> --- /dev/null
> +++ b/include/linux/kmsan.h
> @@ -0,0 +1,47 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * KMSAN API for subsystems.
> + *
> + * Copyright (C) 2017-2022 Google LLC
> + * Author: Alexander Potapenko <glider@google.com>
> + *
> + */
> +#ifndef _LINUX_KMSAN_H
> +#define _LINUX_KMSAN_H
> +
> +#include <linux/gfp.h>
> +#include <linux/kmsan-checks.h>
> +#include <linux/stackdepot.h>
> +#include <linux/types.h>
> +#include <linux/vmalloc.h>
> +
> +struct page;
> +
> +#ifdef CONFIG_KMSAN
> +
> +/* These constants are defined in the MSan LLVM instrumentation pass. */
> +#define KMSAN_RETVAL_SIZE 800
> +#define KMSAN_PARAM_SIZE 800
> +
> +struct kmsan_context_state {
> +	char param_tls[KMSAN_PARAM_SIZE];
> +	char retval_tls[KMSAN_RETVAL_SIZE];
> +	char va_arg_tls[KMSAN_PARAM_SIZE];
> +	char va_arg_origin_tls[KMSAN_PARAM_SIZE];
> +	u64 va_arg_overflow_size_tls;
> +	char param_origin_tls[KMSAN_PARAM_SIZE];
> +	depot_stack_handle_t retval_origin_tls;
> +};
> +
> +#undef KMSAN_PARAM_SIZE
> +#undef KMSAN_RETVAL_SIZE
> +
> +struct kmsan_ctx {
> +	struct kmsan_context_state cstate;
> +	int kmsan_in_runtime;
> +	bool allow_reporting;
> +};
> +
> +#endif
> +
> +#endif /* _LINUX_KMSAN_H */
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 8834e38c06a4f..85c97a2145f7e 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -218,6 +218,18 @@ struct page {
>  					   not kmapped, ie. highmem) */
>  #endif /* WANT_PAGE_VIRTUAL */
>  
> +#ifdef CONFIG_KMSAN
> +	/*
> +	 * KMSAN metadata for this page:
> +	 *  - shadow page: every bit indicates whether the corresponding
> +	 *    bit of the original page is initialized (0) or not (1);
> +	 *  - origin page: every 4 bytes contain an id of the stack trace
> +	 *    where the uninitialized value was created.
> +	 */
> +	struct page *kmsan_shadow;
> +	struct page *kmsan_origin;
> +#endif
> +
>  #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
>  	int _last_cpupid;
>  #endif
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index a8911b1f35aad..9e53624cd73ac 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -14,6 +14,7 @@
>  #include <linux/pid.h>
>  #include <linux/sem.h>
>  #include <linux/shm.h>
> +#include <linux/kmsan.h>
>  #include <linux/mutex.h>
>  #include <linux/plist.h>
>  #include <linux/hrtimer.h>
> @@ -1352,6 +1353,10 @@ struct task_struct {
>  #endif
>  #endif
>  
> +#ifdef CONFIG_KMSAN
> +	struct kmsan_ctx		kmsan_ctx;
> +#endif
> +
>  #if IS_ENABLED(CONFIG_KUNIT)
>  	struct kunit			*kunit_test;
>  #endif
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 075cd25363ac3..b81670878acae 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -996,6 +996,7 @@ config DEBUG_STACKOVERFLOW
>  
>  source "lib/Kconfig.kasan"
>  source "lib/Kconfig.kfence"
> +source "lib/Kconfig.kmsan"
>  
>  endmenu # "Memory Debugging"
>  
> diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
> new file mode 100644
> index 0000000000000..199f79d031f94
> --- /dev/null
> +++ b/lib/Kconfig.kmsan
> @@ -0,0 +1,23 @@

Missing SPDX-License-Identifier.

> +config HAVE_ARCH_KMSAN
> +	bool
> +
> +config HAVE_KMSAN_COMPILER
> +	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=kernel-memory -mllvm -msan-disable-checks=1))
> +
> +config KMSAN
> +	bool "KMSAN: detector of uninitialized values use"
> +	depends on HAVE_ARCH_KMSAN && HAVE_KMSAN_COMPILER
> +	depends on SLUB && DEBUG_KERNEL && !KASAN && !KCSAN
> +	depends on CC_IS_CLANG && CLANG_VERSION >= 140000

Shouldn't the "CC_IS_CLANG && CLANG_VERSION ..." check be a "depends on"
in HAVE_KMSAN_COMPILER? That way all the compiler-related checks are
confined to HAVE_KMSAN_COMPILER.

I guess, it might also be worth mentioning why the version check is
required at all (something about older compilers supporting
fsanitize=kernel-memory, but not having all features we need).

> +	select STACKDEPOT
> +	select STACKDEPOT_ALWAYS_INIT
> +	help
> +	  KernelMemorySanitizer (KMSAN) is a dynamic detector of uses of
> +	  uninitialized values in the kernel. It is based on compiler
> +	  instrumentation provided by Clang and thus requires Clang to build.
> +
> +	  An important note is that KMSAN is not intended for production use,
> +	  because it drastically increases kernel memory footprint and slows
> +	  the whole system down.
> +
> +	  See <file:Documentation/dev-tools/kmsan.rst> for more details.
> diff --git a/mm/Makefile b/mm/Makefile
> index 4cc13f3179a51..4da7eeaecc214 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -89,6 +89,7 @@ obj-$(CONFIG_SLAB) += slab.o
>  obj-$(CONFIG_SLUB) += slub.o
>  obj-$(CONFIG_KASAN)	+= kasan/
>  obj-$(CONFIG_KFENCE) += kfence/
> +obj-$(CONFIG_KMSAN)	+= kmsan/
>  obj-$(CONFIG_FAILSLAB) += failslab.o
>  obj-$(CONFIG_MEMTEST)		+= memtest.o
>  obj-$(CONFIG_MIGRATION) += migrate.o
> diff --git a/mm/kmsan/Makefile b/mm/kmsan/Makefile
> new file mode 100644
> index 0000000000000..a80dde1de7048
> --- /dev/null
> +++ b/mm/kmsan/Makefile
> @@ -0,0 +1,18 @@

Makefile needs a SPDX-License-Identifier.

> +obj-y := core.o instrumentation.o hooks.o report.o shadow.o
> +
> +KMSAN_SANITIZE := n
> +KCOV_INSTRUMENT := n
> +UBSAN_SANITIZE := n
> +
> +# Disable instrumentation of KMSAN runtime with other tools.
> +CC_FLAGS_KMSAN_RUNTIME := -fno-stack-protector
> +CC_FLAGS_KMSAN_RUNTIME += $(call cc-option,-fno-conserve-stack)
> +CC_FLAGS_KMSAN_RUNTIME += -DDISABLE_BRANCH_PROFILING
> +
> +CFLAGS_REMOVE.o = $(CC_FLAGS_FTRACE)
> +
> +CFLAGS_core.o := $(CC_FLAGS_KMSAN_RUNTIME)
> +CFLAGS_hooks.o := $(CC_FLAGS_KMSAN_RUNTIME)
> +CFLAGS_instrumentation.o := $(CC_FLAGS_KMSAN_RUNTIME)
> +CFLAGS_report.o := $(CC_FLAGS_KMSAN_RUNTIME)
> +CFLAGS_shadow.o := $(CC_FLAGS_KMSAN_RUNTIME)
> diff --git a/mm/kmsan/core.c b/mm/kmsan/core.c
> new file mode 100644
> index 0000000000000..933d864d9d467
> --- /dev/null
> +++ b/mm/kmsan/core.c
> @@ -0,0 +1,458 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KMSAN runtime library.
> + *
> + * Copyright (C) 2017-2022 Google LLC
> + * Author: Alexander Potapenko <glider@google.com>
> + *
> + */
> +
> +#include <asm/page.h>
> +#include <linux/compiler.h>
> +#include <linux/export.h>
> +#include <linux/highmem.h>
> +#include <linux/interrupt.h>
> +#include <linux/kernel.h>
> +#include <linux/kmsan.h>
> +#include <linux/memory.h>
> +#include <linux/mm.h>
> +#include <linux/mm_types.h>
> +#include <linux/mmzone.h>
> +#include <linux/percpu-defs.h>
> +#include <linux/preempt.h>
> +#include <linux/slab.h>
> +#include <linux/stackdepot.h>
> +#include <linux/stacktrace.h>
> +#include <linux/types.h>
> +#include <linux/vmalloc.h>
> +
> +#include "../slab.h"
> +#include "kmsan.h"
> +
> +/*
> + * Avoid creating too long origin chains, these are unlikely to participate in
> + * real reports.
> + */
> +#define MAX_CHAIN_DEPTH 7
> +#define NUM_SKIPPED_TO_WARN 10000
> +
> +bool kmsan_enabled __read_mostly;
> +
> +/*
> + * Per-CPU KMSAN context to be used in interrupts, where current->kmsan is
> + * unavaliable.
> + */
> +DEFINE_PER_CPU(struct kmsan_ctx, kmsan_percpu_ctx);
> +
> +void kmsan_internal_poison_memory(void *address, size_t size, gfp_t flags,
> +				  unsigned int poison_flags)
> +{
> +	u32 extra_bits =
> +		kmsan_extra_bits(/*depth*/ 0, poison_flags & KMSAN_POISON_FREE);
> +	bool checked = poison_flags & KMSAN_POISON_CHECK;
> +	depot_stack_handle_t handle;
> +
> +	handle = kmsan_save_stack_with_flags(flags, extra_bits);
> +	kmsan_internal_set_shadow_origin(address, size, -1, handle, checked);
> +}
> +
> +void kmsan_internal_unpoison_memory(void *address, size_t size, bool checked)
> +{
> +	kmsan_internal_set_shadow_origin(address, size, 0, 0, checked);
> +}
> +
> +depot_stack_handle_t kmsan_save_stack_with_flags(gfp_t flags,
> +						 unsigned int extra)
> +{
> +	unsigned long entries[KMSAN_STACK_DEPTH];
> +	unsigned int nr_entries;
> +
> +	nr_entries = stack_trace_save(entries, KMSAN_STACK_DEPTH, 0);
> +
> +	/* Don't sleep (see might_sleep_if() in __alloc_pages_nodemask()). */
> +	flags &= ~__GFP_DIRECT_RECLAIM;
> +
> +	return __stack_depot_save(entries, nr_entries, extra, flags, true);
> +}
> +
> +/* Copy the metadata following the memmove() behavior. */
> +void kmsan_internal_memmove_metadata(void *dst, void *src, size_t n)
> +{
> +	depot_stack_handle_t old_origin = 0, new_origin = 0;
> +	int src_slots, dst_slots, i, iter, step, skip_bits;
> +	depot_stack_handle_t *origin_src, *origin_dst;
> +	void *shadow_src, *shadow_dst;
> +	u32 *align_shadow_src, shadow;
> +	bool backwards;
> +
> +	shadow_dst = kmsan_get_metadata(dst, KMSAN_META_SHADOW);
> +	if (!shadow_dst)
> +		return;
> +	KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(dst, n));
> +
> +	shadow_src = kmsan_get_metadata(src, KMSAN_META_SHADOW);
> +	if (!shadow_src) {
> +		/*
> +		 * |src| is untracked: zero out destination shadow, ignore the

Probably doesn't matter too much, but for consistency elsewhere - @src?

> +		 * origins, we're done.
> +		 */
> +		__memset(shadow_dst, 0, n);
> +		return;
> +	}
> +	KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(src, n));
> +
> +	__memmove(shadow_dst, shadow_src, n);
> +
> +	origin_dst = kmsan_get_metadata(dst, KMSAN_META_ORIGIN);
> +	origin_src = kmsan_get_metadata(src, KMSAN_META_ORIGIN);
> +	KMSAN_WARN_ON(!origin_dst || !origin_src);
> +	src_slots = (ALIGN((u64)src + n, KMSAN_ORIGIN_SIZE) -
> +		     ALIGN_DOWN((u64)src, KMSAN_ORIGIN_SIZE)) /
> +		    KMSAN_ORIGIN_SIZE;
> +	dst_slots = (ALIGN((u64)dst + n, KMSAN_ORIGIN_SIZE) -
> +		     ALIGN_DOWN((u64)dst, KMSAN_ORIGIN_SIZE)) /
> +		    KMSAN_ORIGIN_SIZE;
> +	KMSAN_WARN_ON((src_slots < 1) || (dst_slots < 1));
> +	KMSAN_WARN_ON((src_slots - dst_slots > 1) ||
> +		      (dst_slots - src_slots < -1));
> +
> +	backwards = dst > src;
> +	i = backwards ? min(src_slots, dst_slots) - 1 : 0;
> +	iter = backwards ? -1 : 1;
> +
> +	align_shadow_src =
> +		(u32 *)ALIGN_DOWN((u64)shadow_src, KMSAN_ORIGIN_SIZE);
> +	for (step = 0; step < min(src_slots, dst_slots); step++, i += iter) {
> +		KMSAN_WARN_ON(i < 0);
> +		shadow = align_shadow_src[i];
> +		if (i == 0) {
> +			/*
> +			 * If |src| isn't aligned on KMSAN_ORIGIN_SIZE, don't
> +			 * look at the first |src % KMSAN_ORIGIN_SIZE| bytes
> +			 * of the first shadow slot.
> +			 */
> +			skip_bits = ((u64)src % KMSAN_ORIGIN_SIZE) * 8;
> +			shadow = (shadow >> skip_bits) << skip_bits;
> +		}
> +		if (i == src_slots - 1) {
> +			/*
> +			 * If |src + n| isn't aligned on
> +			 * KMSAN_ORIGIN_SIZE, don't look at the last
> +			 * |(src + n) % KMSAN_ORIGIN_SIZE| bytes of the
> +			 * last shadow slot.
> +			 */
> +			skip_bits = (((u64)src + n) % KMSAN_ORIGIN_SIZE) * 8;
> +			shadow = (shadow << skip_bits) >> skip_bits;
> +		}
> +		/*
> +		 * Overwrite the origin only if the corresponding
> +		 * shadow is nonempty.
> +		 */
> +		if (origin_src[i] && (origin_src[i] != old_origin) && shadow) {
> +			old_origin = origin_src[i];
> +			new_origin = kmsan_internal_chain_origin(old_origin);
> +			/*
> +			 * kmsan_internal_chain_origin() may return
> +			 * NULL, but we don't want to lose the previous
> +			 * origin value.
> +			 */
> +			if (!new_origin)
> +				new_origin = old_origin;
> +		}
> +		if (shadow)
> +			origin_dst[i] = new_origin;
> +		else
> +			origin_dst[i] = 0;
> +	}
> +	/*
> +	 * If dst_slots is greater than src_slots (i.e.
> +	 * dst_slots == src_slots + 1), there is an extra origin slot at the
> +	 * beginning or end of the destination buffer, for which we take the
> +	 * origin from the previous slot.
> +	 * This is only done if the part of the source shadow corresponding to
> +	 * slot is non-zero.
> +	 *
> +	 * E.g. if we copy 8 aligned bytes that are marked as uninitialized
> +	 * and have origins o111 and o222, to an unaligned buffer with offset 1,
> +	 * these two origins are copied to three origin slots, so one of then
> +	 * needs to be duplicated, depending on the copy direction (@backwards)
> +	 *
> +	 *   src shadow: |uuuu|uuuu|....|
> +	 *   src origin: |o111|o222|....|
> +	 *
> +	 * backwards = 0:
> +	 *   dst shadow: |.uuu|uuuu|u...|
> +	 *   dst origin: |....|o111|o222| - fill the empty slot with o111
> +	 * backwards = 1:
> +	 *   dst shadow: |.uuu|uuuu|u...|
> +	 *   dst origin: |o111|o222|....| - fill the empty slot with o222
> +	 */
> +	if (src_slots < dst_slots) {
> +		if (backwards) {
> +			shadow = align_shadow_src[src_slots - 1];
> +			skip_bits = (((u64)dst + n) % KMSAN_ORIGIN_SIZE) * 8;
> +			shadow = (shadow << skip_bits) >> skip_bits;
> +			if (shadow)
> +				/* src_slots > 0, therefore dst_slots is at least 2 */
> +				origin_dst[dst_slots - 1] = origin_dst[dst_slots - 2];
> +		} else {
> +			shadow = align_shadow_src[0];
> +			skip_bits = ((u64)dst % KMSAN_ORIGIN_SIZE) * 8;
> +			shadow = (shadow >> skip_bits) << skip_bits;
> +			if (shadow)
> +				origin_dst[0] = origin_dst[1];
> +		}
> +	}
> +}
> +
> +depot_stack_handle_t kmsan_internal_chain_origin(depot_stack_handle_t id)
> +{
> +	unsigned long entries[3];
> +	u32 extra_bits;
> +	int depth;
> +	bool uaf;
> +
> +	if (!id)
> +		return id;
> +	/*
> +	 * Make sure we have enough spare bits in |id| to hold the UAF bit and
> +	 * the chain depth.
> +	 */
> +	BUILD_BUG_ON((1 << STACK_DEPOT_EXTRA_BITS) <= (MAX_CHAIN_DEPTH << 1));
> +
> +	extra_bits = stack_depot_get_extra_bits(id);
> +	depth = kmsan_depth_from_eb(extra_bits);
> +	uaf = kmsan_uaf_from_eb(extra_bits);
> +
> +	if (depth >= MAX_CHAIN_DEPTH) {
> +		static atomic_long_t kmsan_skipped_origins;
> +		long skipped = atomic_long_inc_return(&kmsan_skipped_origins);
> +
> +		if (skipped % NUM_SKIPPED_TO_WARN == 0) {
> +			pr_warn("not chained %ld origins\n", skipped);
> +			dump_stack();
> +			kmsan_print_origin(id);
> +		}
> +		return id;
> +	}
> +	depth++;
> +	extra_bits = kmsan_extra_bits(depth, uaf);
> +
> +	entries[0] = KMSAN_CHAIN_MAGIC_ORIGIN;
> +	entries[1] = kmsan_save_stack_with_flags(GFP_ATOMIC, 0);
> +	entries[2] = id;
> +	/*
> +	 * @entries is a local var in non-instrumented code, so KMSAN does not
> +	 * know it is initialized. Explicitly unpoison it to avoid false
> +	 * positives when __stack_depot_save() passes it to instrumented code.
> +	 */
> +	kmsan_internal_unpoison_memory(entries, sizeof(entries), false);
> +	return __stack_depot_save(entries, ARRAY_SIZE(entries), extra_bits,
> +				  GFP_ATOMIC, true);
> +}
> +
> +void kmsan_internal_set_shadow_origin(void *addr, size_t size, int b,
> +				      u32 origin, bool checked)
> +{
> +	u64 address = (u64)addr;
> +	void *shadow_start;
> +	u32 *origin_start;
> +	size_t pad = 0;
> +	int i;
> +
> +	KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size));
> +	shadow_start = kmsan_get_metadata(addr, KMSAN_META_SHADOW);
> +	if (!shadow_start) {
> +		/*
> +		 * kmsan_metadata_is_contiguous() is true, so either all shadow
> +		 * and origin pages are NULL, or all are non-NULL.
> +		 */
> +		if (checked) {
> +			pr_err("%s: not memsetting %ld bytes starting at %px, because the shadow is NULL\n",
> +			       __func__, size, addr);
> +			KMSAN_WARN_ON(true);
> +		}
> +		return;
> +	}
> +	__memset(shadow_start, b, size);
> +
> +	if (!IS_ALIGNED(address, KMSAN_ORIGIN_SIZE)) {
> +		pad = address % KMSAN_ORIGIN_SIZE;
> +		address -= pad;
> +		size += pad;
> +	}
> +	size = ALIGN(size, KMSAN_ORIGIN_SIZE);
> +	origin_start =
> +		(u32 *)kmsan_get_metadata((void *)address, KMSAN_META_ORIGIN);
> +
> +	for (i = 0; i < size / KMSAN_ORIGIN_SIZE; i++)
> +		origin_start[i] = origin;
> +}
> +
> +struct page *kmsan_vmalloc_to_page_or_null(void *vaddr)
> +{
> +	struct page *page;
> +
> +	if (!kmsan_internal_is_vmalloc_addr(vaddr) &&
> +	    !kmsan_internal_is_module_addr(vaddr))
> +		return NULL;
> +	page = vmalloc_to_page(vaddr);
> +	if (pfn_valid(page_to_pfn(page)))
> +		return page;
> +	else
> +		return NULL;
> +}
> +
> +void kmsan_internal_check_memory(void *addr, size_t size, const void *user_addr,
> +				 int reason)
> +{
> +	depot_stack_handle_t cur_origin = 0, new_origin = 0;
> +	unsigned long addr64 = (unsigned long)addr;
> +	depot_stack_handle_t *origin = NULL;
> +	unsigned char *shadow = NULL;
> +	int cur_off_start = -1;
> +	int i, chunk_size;
> +	size_t pos = 0;
> +
> +	if (!size)
> +		return;
> +	KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size));
> +	while (pos < size) {
> +		chunk_size = min(size - pos,
> +				 PAGE_SIZE - ((addr64 + pos) % PAGE_SIZE));
> +		shadow = kmsan_get_metadata((void *)(addr64 + pos),
> +					    KMSAN_META_SHADOW);
> +		if (!shadow) {
> +			/*
> +			 * This page is untracked. If there were uninitialized
> +			 * bytes before, report them.
> +			 */
> +			if (cur_origin) {
> +				kmsan_enter_runtime();
> +				kmsan_report(cur_origin, addr, size,
> +					     cur_off_start, pos - 1, user_addr,
> +					     reason);
> +				kmsan_leave_runtime();
> +			}
> +			cur_origin = 0;
> +			cur_off_start = -1;
> +			pos += chunk_size;
> +			continue;
> +		}
> +		for (i = 0; i < chunk_size; i++) {
> +			if (!shadow[i]) {
> +				/*
> +				 * This byte is unpoisoned. If there were
> +				 * poisoned bytes before, report them.
> +				 */
> +				if (cur_origin) {
> +					kmsan_enter_runtime();
> +					kmsan_report(cur_origin, addr, size,
> +						     cur_off_start, pos + i - 1,
> +						     user_addr, reason);
> +					kmsan_leave_runtime();
> +				}
> +				cur_origin = 0;
> +				cur_off_start = -1;
> +				continue;
> +			}
> +			origin = kmsan_get_metadata((void *)(addr64 + pos + i),
> +						    KMSAN_META_ORIGIN);
> +			KMSAN_WARN_ON(!origin);
> +			new_origin = *origin;
> +			/*
> +			 * Encountered new origin - report the previous
> +			 * uninitialized range.
> +			 */
> +			if (cur_origin != new_origin) {
> +				if (cur_origin) {
> +					kmsan_enter_runtime();
> +					kmsan_report(cur_origin, addr, size,
> +						     cur_off_start, pos + i - 1,
> +						     user_addr, reason);
> +					kmsan_leave_runtime();
> +				}
> +				cur_origin = new_origin;
> +				cur_off_start = pos + i;
> +			}
> +		}
> +		pos += chunk_size;
> +	}
> +	KMSAN_WARN_ON(pos != size);
> +	if (cur_origin) {
> +		kmsan_enter_runtime();
> +		kmsan_report(cur_origin, addr, size, cur_off_start, pos - 1,
> +			     user_addr, reason);
> +		kmsan_leave_runtime();
> +	}
> +}
> +
> +bool kmsan_metadata_is_contiguous(void *addr, size_t size)
> +{
> +	char *cur_shadow = NULL, *next_shadow = NULL, *cur_origin = NULL,
> +	     *next_origin = NULL;
> +	u64 cur_addr = (u64)addr, next_addr = cur_addr + PAGE_SIZE;
> +	depot_stack_handle_t *origin_p;
> +	bool all_untracked = false;
> +
> +	if (!size)
> +		return true;
> +
> +	/* The whole range belongs to the same page. */
> +	if (ALIGN_DOWN(cur_addr + size - 1, PAGE_SIZE) ==
> +	    ALIGN_DOWN(cur_addr, PAGE_SIZE))
> +		return true;
> +
> +	cur_shadow = kmsan_get_metadata((void *)cur_addr, /*is_origin*/ false);
> +	if (!cur_shadow)
> +		all_untracked = true;
> +	cur_origin = kmsan_get_metadata((void *)cur_addr, /*is_origin*/ true);
> +	if (all_untracked && cur_origin)
> +		goto report;
> +
> +	for (; next_addr < (u64)addr + size;
> +	     cur_addr = next_addr, cur_shadow = next_shadow,
> +	     cur_origin = next_origin, next_addr += PAGE_SIZE) {
> +		next_shadow = kmsan_get_metadata((void *)next_addr, false);
> +		next_origin = kmsan_get_metadata((void *)next_addr, true);
> +		if (all_untracked) {
> +			if (next_shadow || next_origin)
> +				goto report;
> +			if (!next_shadow && !next_origin)
> +				continue;
> +		}
> +		if (((u64)cur_shadow == ((u64)next_shadow - PAGE_SIZE)) &&
> +		    ((u64)cur_origin == ((u64)next_origin - PAGE_SIZE)))
> +			continue;
> +		goto report;
> +	}
> +	return true;
> +
> +report:
> +	pr_err("%s: attempting to access two shadow page ranges.\n", __func__);
> +	pr_err("Access of size %ld at %px.\n", size, addr);
> +	pr_err("Addresses belonging to different ranges: %px and %px\n",
> +	       (void *)cur_addr, (void *)next_addr);
> +	pr_err("page[0].shadow: %px, page[1].shadow: %px\n", cur_shadow,
> +	       next_shadow);
> +	pr_err("page[0].origin: %px, page[1].origin: %px\n", cur_origin,
> +	       next_origin);
> +	origin_p = kmsan_get_metadata(addr, KMSAN_META_ORIGIN);
> +	if (origin_p) {
> +		pr_err("Origin: %08x\n", *origin_p);
> +		kmsan_print_origin(*origin_p);
> +	} else {
> +		pr_err("Origin: unavailable\n");
> +	}
> +	return false;
> +}
> +
> +bool kmsan_internal_is_module_addr(void *vaddr)
> +{
> +	return ((u64)vaddr >= MODULES_VADDR) && ((u64)vaddr < MODULES_END);
> +}
> +
> +bool kmsan_internal_is_vmalloc_addr(void *addr)
> +{
> +	return ((u64)addr >= VMALLOC_START) && ((u64)addr < VMALLOC_END);
> +}
> diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
> new file mode 100644
> index 0000000000000..4ac62fa67a02a
> --- /dev/null
> +++ b/mm/kmsan/hooks.c
> @@ -0,0 +1,66 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KMSAN hooks for kernel subsystems.
> + *
> + * These functions handle creation of KMSAN metadata for memory allocations.
> + *
> + * Copyright (C) 2018-2022 Google LLC
> + * Author: Alexander Potapenko <glider@google.com>
> + *
> + */
> +
> +#include <linux/cacheflush.h>
> +#include <linux/gfp.h>
> +#include <linux/mm.h>
> +#include <linux/mm_types.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +
> +#include "../internal.h"
> +#include "../slab.h"
> +#include "kmsan.h"
> +
> +/*
> + * Instrumented functions shouldn't be called under
> + * kmsan_enter_runtime()/kmsan_leave_runtime(), because this will lead to
> + * skipping effects of functions like memset() inside instrumented code.
> + */
> +
> +/* Functions from kmsan-checks.h follow. */
> +void kmsan_poison_memory(const void *address, size_t size, gfp_t flags)
> +{
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return;
> +	kmsan_enter_runtime();
> +	/* The users may want to poison/unpoison random memory. */
> +	kmsan_internal_poison_memory((void *)address, size, flags,
> +				     KMSAN_POISON_NOCHECK);
> +	kmsan_leave_runtime();
> +}
> +EXPORT_SYMBOL(kmsan_poison_memory);
> +
> +void kmsan_unpoison_memory(const void *address, size_t size)
> +{
> +	unsigned long ua_flags;
> +
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return;
> +
> +	ua_flags = user_access_save();
> +	kmsan_enter_runtime();
> +	/* The users may want to poison/unpoison random memory. */
> +	kmsan_internal_unpoison_memory((void *)address, size,
> +				       KMSAN_POISON_NOCHECK);
> +	kmsan_leave_runtime();
> +	user_access_restore(ua_flags);
> +}
> +EXPORT_SYMBOL(kmsan_unpoison_memory);
> +
> +void kmsan_check_memory(const void *addr, size_t size)
> +{
> +	if (!kmsan_enabled)
> +		return;
> +	return kmsan_internal_check_memory((void *)addr, size, /*user_addr*/ 0,
> +					   REASON_ANY);
> +}
> +EXPORT_SYMBOL(kmsan_check_memory);
> diff --git a/mm/kmsan/instrumentation.c b/mm/kmsan/instrumentation.c
> new file mode 100644
> index 0000000000000..fe062d123a76f
> --- /dev/null
> +++ b/mm/kmsan/instrumentation.c
> @@ -0,0 +1,267 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KMSAN compiler API.
> + *
> + * This file implements __msan_XXX hooks that Clang inserts into the code
> + * compiled with -fsanitize=kernel-memory.
> + * See Documentation/dev-tools/kmsan.rst for more information on how KMSAN
> + * instrumentation works.
> + *
> + * Copyright (C) 2017-2022 Google LLC
> + * Author: Alexander Potapenko <glider@google.com>
> + *
> + */
> +
> +#include "kmsan.h"
> +#include <linux/gfp.h>
> +#include <linux/mm.h>
> +#include <linux/uaccess.h>
> +
> +static inline bool is_bad_asm_addr(void *addr, uintptr_t size, bool is_store)
> +{
> +	if ((u64)addr < TASK_SIZE)
> +		return true;
> +	if (!kmsan_get_metadata(addr, KMSAN_META_SHADOW))
> +		return true;
> +	return false;
> +}
> +
> +static inline struct shadow_origin_ptr
> +get_shadow_origin_ptr(void *addr, u64 size, bool store)
> +{
> +	unsigned long ua_flags = user_access_save();
> +	struct shadow_origin_ptr ret;
> +
> +	ret = kmsan_get_shadow_origin_ptr(addr, size, store);
> +	user_access_restore(ua_flags);
> +	return ret;
> +}
> +
> +/* Get shadow and origin pointers for a memory load with non-standard size. */
> +struct shadow_origin_ptr __msan_metadata_ptr_for_load_n(void *addr,
> +							uintptr_t size)
> +{
> +	return get_shadow_origin_ptr(addr, size, /*store*/ false);
> +}
> +EXPORT_SYMBOL(__msan_metadata_ptr_for_load_n);
> +
> +/* Get shadow and origin pointers for a memory store with non-standard size. */
> +struct shadow_origin_ptr __msan_metadata_ptr_for_store_n(void *addr,
> +							 uintptr_t size)
> +{
> +	return get_shadow_origin_ptr(addr, size, /*store*/ true);
> +}
> +EXPORT_SYMBOL(__msan_metadata_ptr_for_store_n);
> +
> +/*
> + * Declare functions that obtain shadow/origin pointers for loads and stores
> + * with fixed size.
> + */
> +#define DECLARE_METADATA_PTR_GETTER(size)                                      \
> +	struct shadow_origin_ptr __msan_metadata_ptr_for_load_##size(          \
> +		void *addr)                                                    \
> +	{                                                                      \
> +		return get_shadow_origin_ptr(addr, size, /*store*/ false);     \
> +	}                                                                      \
> +	EXPORT_SYMBOL(__msan_metadata_ptr_for_load_##size);                    \
> +	struct shadow_origin_ptr __msan_metadata_ptr_for_store_##size(         \
> +		void *addr)                                                    \
> +	{                                                                      \
> +		return get_shadow_origin_ptr(addr, size, /*store*/ true);      \
> +	}                                                                      \
> +	EXPORT_SYMBOL(__msan_metadata_ptr_for_store_##size)
> +
> +DECLARE_METADATA_PTR_GETTER(1);
> +DECLARE_METADATA_PTR_GETTER(2);
> +DECLARE_METADATA_PTR_GETTER(4);
> +DECLARE_METADATA_PTR_GETTER(8);
> +
> +/*
> + * Handle a memory store performed by inline assembly. KMSAN conservatively
> + * attempts to unpoison the outputs of asm() directives to prevent false
> + * positives caused by missed stores.
> + */
> +void __msan_instrument_asm_store(void *addr, uintptr_t size)
> +{
> +	unsigned long ua_flags;
> +
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return;
> +
> +	ua_flags = user_access_save();
> +	/*
> +	 * Most of the accesses are below 32 bytes. The two exceptions so far
> +	 * are clwb() (64 bytes) and FPU state (512 bytes).
> +	 * It's unlikely that the assembly will touch more than 512 bytes.
> +	 */
> +	if (size > 512) {
> +		WARN_ONCE(1, "assembly store size too big: %ld\n", size);
> +		size = 8;
> +	}
> +	if (is_bad_asm_addr(addr, size, /*is_store*/ true)) {
> +		user_access_restore(ua_flags);
> +		return;
> +	}
> +	kmsan_enter_runtime();
> +	/* Unpoisoning the memory on best effort. */
> +	kmsan_internal_unpoison_memory(addr, size, /*checked*/ false);
> +	kmsan_leave_runtime();
> +	user_access_restore(ua_flags);
> +}
> +EXPORT_SYMBOL(__msan_instrument_asm_store);
> +
> +/* Handle llvm.memmove intrinsic. */
> +void *__msan_memmove(void *dst, const void *src, uintptr_t n)
> +{
> +	void *result;
> +
> +	result = __memmove(dst, src, n);
> +	if (!n)
> +		/* Some people call memmove() with zero length. */
> +		return result;
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return result;
> +
> +	kmsan_internal_memmove_metadata(dst, (void *)src, n);
> +
> +	return result;
> +}
> +EXPORT_SYMBOL(__msan_memmove);
> +
> +/* Handle llvm.memcpy intrinsic. */
> +void *__msan_memcpy(void *dst, const void *src, uintptr_t n)
> +{
> +	void *result;
> +
> +	result = __memcpy(dst, src, n);
> +	if (!n)
> +		/* Some people call memcpy() with zero length. */
> +		return result;
> +
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return result;
> +
> +	/* Using memmove instead of memcpy doesn't affect correctness. */
> +	kmsan_internal_memmove_metadata(dst, (void *)src, n);
> +
> +	return result;
> +}
> +EXPORT_SYMBOL(__msan_memcpy);
> +
> +/* Handle llvm.memset intrinsic. */
> +void *__msan_memset(void *dst, int c, uintptr_t n)
> +{
> +	void *result;
> +
> +	result = __memset(dst, c, n);
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return result;
> +
> +	kmsan_enter_runtime();
> +	/*
> +	 * Clang doesn't pass parameter metadata here, so it is impossible to
> +	 * use shadow of @c to set up the shadow for @dst.
> +	 */
> +	kmsan_internal_unpoison_memory(dst, n, /*checked*/ false);
> +	kmsan_leave_runtime();
> +
> +	return result;
> +}
> +EXPORT_SYMBOL(__msan_memset);
> +
> +/*
> + * Create a new origin from an old one. This is done when storing an
> + * uninitialized value to memory. When reporting an error, KMSAN unrolls and
> + * prints the whole chain of stores that preceded the use of this value.
> + */
> +depot_stack_handle_t __msan_chain_origin(depot_stack_handle_t origin)
> +{
> +	depot_stack_handle_t ret = 0;
> +	unsigned long ua_flags;
> +
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return ret;
> +
> +	ua_flags = user_access_save();
> +
> +	/* Creating new origins may allocate memory. */
> +	kmsan_enter_runtime();
> +	ret = kmsan_internal_chain_origin(origin);
> +	kmsan_leave_runtime();
> +	user_access_restore(ua_flags);
> +	return ret;
> +}
> +EXPORT_SYMBOL(__msan_chain_origin);
> +
> +/* Poison a local variable when entering a function. */
> +void __msan_poison_alloca(void *address, uintptr_t size, char *descr)
> +{
> +	depot_stack_handle_t handle;
> +	unsigned long entries[4];
> +	unsigned long ua_flags;
> +
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return;
> +
> +	ua_flags = user_access_save();
> +	entries[0] = KMSAN_ALLOCA_MAGIC_ORIGIN;
> +	entries[1] = (u64)descr;
> +	entries[2] = (u64)__builtin_return_address(0);
> +	/*
> +	 * With frame pointers enabled, it is possible to quickly fetch the
> +	 * second frame of the caller stack without calling the unwinder.
> +	 * Without them, simply do not bother.
> +	 */
> +	if (IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER))
> +		entries[3] = (u64)__builtin_return_address(1);
> +	else
> +		entries[3] = 0;
> +
> +	/* stack_depot_save() may allocate memory. */
> +	kmsan_enter_runtime();
> +	handle = stack_depot_save(entries, ARRAY_SIZE(entries), GFP_ATOMIC);
> +	kmsan_leave_runtime();
> +
> +	kmsan_internal_set_shadow_origin(address, size, -1, handle,
> +					 /*checked*/ true);
> +	user_access_restore(ua_flags);
> +}
> +EXPORT_SYMBOL(__msan_poison_alloca);
> +
> +/* Unpoison a local variable. */
> +void __msan_unpoison_alloca(void *address, uintptr_t size)
> +{
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return;
> +
> +	kmsan_enter_runtime();
> +	kmsan_internal_unpoison_memory(address, size, /*checked*/ true);
> +	kmsan_leave_runtime();
> +}
> +EXPORT_SYMBOL(__msan_unpoison_alloca);
> +
> +/*
> + * Report that an uninitialized value with the given origin was used in a way
> + * that constituted undefined behavior.
> + */
> +void __msan_warning(u32 origin)
> +{
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return;
> +	kmsan_enter_runtime();
> +	kmsan_report(origin, /*address*/ 0, /*size*/ 0,
> +		     /*off_first*/ 0, /*off_last*/ 0, /*user_addr*/ 0,
> +		     REASON_ANY);
> +	kmsan_leave_runtime();
> +}
> +EXPORT_SYMBOL(__msan_warning);
> +
> +/*
> + * At the beginning of an instrumented function, obtain the pointer to
> + * `struct kmsan_context_state` holding the metadata for function parameters.
> + */
> +struct kmsan_context_state *__msan_get_context_state(void)
> +{
> +	return &kmsan_get_context()->cstate;
> +}
> +EXPORT_SYMBOL(__msan_get_context_state);
> diff --git a/mm/kmsan/kmsan.h b/mm/kmsan/kmsan.h
> new file mode 100644
> index 0000000000000..bfe38789950a6
> --- /dev/null
> +++ b/mm/kmsan/kmsan.h
> @@ -0,0 +1,183 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Functions used by the KMSAN runtime.
> + *
> + * Copyright (C) 2017-2022 Google LLC
> + * Author: Alexander Potapenko <glider@google.com>
> + *
> + */
> +
> +#ifndef __MM_KMSAN_KMSAN_H
> +#define __MM_KMSAN_KMSAN_H
> +
> +#include <asm/pgtable_64_types.h>
> +#include <linux/irqflags.h>
> +#include <linux/sched.h>
> +#include <linux/stackdepot.h>
> +#include <linux/stacktrace.h>
> +#include <linux/nmi.h>
> +#include <linux/mm.h>
> +#include <linux/printk.h>
> +
> +#define KMSAN_ALLOCA_MAGIC_ORIGIN 0xabcd0100
> +#define KMSAN_CHAIN_MAGIC_ORIGIN 0xabcd0200
> +
> +#define KMSAN_POISON_NOCHECK 0x0
> +#define KMSAN_POISON_CHECK 0x1
> +#define KMSAN_POISON_FREE 0x2
> +
> +#define KMSAN_ORIGIN_SIZE 4
> +
> +#define KMSAN_STACK_DEPTH 64
> +
> +#define KMSAN_META_SHADOW (false)
> +#define KMSAN_META_ORIGIN (true)
> +
> +extern bool kmsan_enabled;
> +extern int panic_on_kmsan;
> +
> +/*
> + * KMSAN performs a lot of consistency checks that are currently enabled by
> + * default. BUG_ON is normally discouraged in the kernel, unless used for
> + * debugging, but KMSAN itself is a debugging tool, so it makes little sense to
> + * recover if something goes wrong.
> + */
> +#define KMSAN_WARN_ON(cond)                                                    \
> +	({                                                                     \
> +		const bool __cond = WARN_ON(cond);                             \
> +		if (unlikely(__cond)) {                                        \
> +			WRITE_ONCE(kmsan_enabled, false);                      \
> +			if (panic_on_kmsan) {                                  \
> +				/* Can't call panic() here because */          \
> +				/* of uaccess checks.*/                        \

space after '.'

> +				BUG();                                         \
> +			}                                                      \
> +		}                                                              \
> +		__cond;                                                        \
> +	})
> +
> +/*
> + * A pair of metadata pointers to be returned by the instrumentation functions.
> + */
> +struct shadow_origin_ptr {
> +	void *shadow, *origin;
> +};
> +
> +struct shadow_origin_ptr kmsan_get_shadow_origin_ptr(void *addr, u64 size,
> +						     bool store);
> +void *kmsan_get_metadata(void *addr, bool is_origin);
> +
> +enum kmsan_bug_reason {
> +	REASON_ANY,
> +	REASON_COPY_TO_USER,
> +	REASON_SUBMIT_URB,
> +};
> +
> +void kmsan_print_origin(depot_stack_handle_t origin);
> +
> +/**
> + * kmsan_report() - Report a use of uninitialized value.
> + * @origin:    Stack ID of the uninitialized value.
> + * @address:   Address at which the memory access happens.
> + * @size:      Memory access size.
> + * @off_first: Offset (from @address) of the first byte to be reported.
> + * @off_last:  Offset (from @address) of the last byte to be reported.
> + * @user_addr: When non-NULL, denotes the userspace address to which the kernel
> + *             is leaking data.
> + * @reason:    Error type from enum kmsan_bug_reason.
> + *
> + * kmsan_report() prints an error message for a consequent group of bytes
> + * sharing the same origin. If an uninitialized value is used in a comparison,
> + * this function is called once without specifying the addresses. When checking
> + * a memory range, KMSAN may call kmsan_report() multiple times with the same
> + * @address, @size, @user_addr and @reason, but different @off_first and
> + * @off_last corresponding to different @origin values.
> + */
> +void kmsan_report(depot_stack_handle_t origin, void *address, int size,
> +		  int off_first, int off_last, const void *user_addr,
> +		  enum kmsan_bug_reason reason);
> +
> +DECLARE_PER_CPU(struct kmsan_ctx, kmsan_percpu_ctx);
> +
> +static __always_inline struct kmsan_ctx *kmsan_get_context(void)
> +{
> +	return in_task() ? &current->kmsan_ctx : raw_cpu_ptr(&kmsan_percpu_ctx);
> +}
> +
> +/*
> + * When a compiler hook is invoked, it may make a call to instrumented code
> + * and eventually call itself recursively. To avoid that, we protect the
> + * runtime entry points with kmsan_enter_runtime()/kmsan_leave_runtime() and
> + * exit the hook if kmsan_in_runtime() is true.
> + */
> +
> +static __always_inline bool kmsan_in_runtime(void)
> +{
> +	if ((hardirq_count() >> HARDIRQ_SHIFT) > 1)
> +		return true;
> +	return kmsan_get_context()->kmsan_in_runtime;
> +}
> +
> +static __always_inline void kmsan_enter_runtime(void)
> +{
> +	struct kmsan_ctx *ctx;
> +
> +	ctx = kmsan_get_context();
> +	KMSAN_WARN_ON(ctx->kmsan_in_runtime++);
> +}
> +
> +static __always_inline void kmsan_leave_runtime(void)
> +{
> +	struct kmsan_ctx *ctx = kmsan_get_context();
> +
> +	KMSAN_WARN_ON(--ctx->kmsan_in_runtime);
> +}
> +
> +depot_stack_handle_t kmsan_save_stack(void);
> +depot_stack_handle_t kmsan_save_stack_with_flags(gfp_t flags,
> +						 unsigned int extra_bits);
> +
> +/*
> + * Pack and unpack the origin chain depth and UAF flag to/from the extra bits
> + * provided by the stack depot.
> + * The UAF flag is stored in the lowest bit, followed by the depth in the upper
> + * bits.
> + * set_dsh_extra_bits() is responsible for clamping the value.
> + */
> +static __always_inline unsigned int kmsan_extra_bits(unsigned int depth,
> +						     bool uaf)
> +{
> +	return (depth << 1) | uaf;
> +}
> +
> +static __always_inline bool kmsan_uaf_from_eb(unsigned int extra_bits)
> +{
> +	return extra_bits & 1;
> +}
> +
> +static __always_inline unsigned int kmsan_depth_from_eb(unsigned int extra_bits)
> +{
> +	return extra_bits >> 1;
> +}
> +
> +/*
> + * kmsan_internal_ functions are supposed to be very simple and not require the
> + * kmsan_in_runtime() checks.
> + */
> +void kmsan_internal_memmove_metadata(void *dst, void *src, size_t n);
> +void kmsan_internal_poison_memory(void *address, size_t size, gfp_t flags,
> +				  unsigned int poison_flags);
> +void kmsan_internal_unpoison_memory(void *address, size_t size, bool checked);
> +void kmsan_internal_set_shadow_origin(void *address, size_t size, int b,
> +				      u32 origin, bool checked);
> +depot_stack_handle_t kmsan_internal_chain_origin(depot_stack_handle_t id);
> +
> +bool kmsan_metadata_is_contiguous(void *addr, size_t size);
> +void kmsan_internal_check_memory(void *addr, size_t size, const void *user_addr,
> +				 int reason);
> +bool kmsan_internal_is_module_addr(void *vaddr);
> +bool kmsan_internal_is_vmalloc_addr(void *addr);
> +
> +struct page *kmsan_vmalloc_to_page_or_null(void *vaddr);
> +
> +#endif /* __MM_KMSAN_KMSAN_H */
> diff --git a/mm/kmsan/report.c b/mm/kmsan/report.c
> new file mode 100644
> index 0000000000000..f36fca452e313
> --- /dev/null
> +++ b/mm/kmsan/report.c
> @@ -0,0 +1,211 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KMSAN error reporting routines.
> + *
> + * Copyright (C) 2019-2022 Google LLC
> + * Author: Alexander Potapenko <glider@google.com>
> + *
> + */
> +
> +#include <linux/console.h>
> +#include <linux/moduleparam.h>
> +#include <linux/stackdepot.h>
> +#include <linux/stacktrace.h>
> +#include <linux/uaccess.h>
> +
> +#include "kmsan.h"
> +
> +static DEFINE_SPINLOCK(kmsan_report_lock);
> +#define DESCR_SIZE 128
> +/* Protected by kmsan_report_lock */
> +static char report_local_descr[DESCR_SIZE];
> +int panic_on_kmsan __read_mostly;
> +
> +#ifdef MODULE_PARAM_PREFIX
> +#undef MODULE_PARAM_PREFIX
> +#endif
> +#define MODULE_PARAM_PREFIX "kmsan."
> +module_param_named(panic, panic_on_kmsan, int, 0);
> +
> +/*
> + * Skip internal KMSAN frames.
> + */
> +static int get_stack_skipnr(const unsigned long stack_entries[],
> +			    int num_entries)
> +{
> +	int len, skip;
> +	char buf[64];
> +
> +	for (skip = 0; skip < num_entries; ++skip) {
> +		len = scnprintf(buf, sizeof(buf), "%ps",
> +				(void *)stack_entries[skip]);
> +
> +		/* Never show __msan_* or kmsan_* functions. */
> +		if ((strnstr(buf, "__msan_", len) == buf) ||
> +		    (strnstr(buf, "kmsan_", len) == buf))
> +			continue;
> +
> +		/*
> +		 * No match for runtime functions -- @skip entries to skip to
> +		 * get to first frame of interest.
> +		 */
> +		break;
> +	}
> +
> +	return skip;
> +}
> +
> +/*
> + * Currently the descriptions of locals generated by Clang look as follows:
> + *   ----local_name@function_name
> + * We want to print only the name of the local, as other information in that
> + * description can be confusing.
> + * The meaningful part of the description is copied to a global buffer to avoid
> + * allocating memory.
> + */
> +static char *pretty_descr(char *descr)
> +{
> +	int i, pos = 0, len = strlen(descr);
> +
> +	for (i = 0; i < len; i++) {
> +		if (descr[i] == '@')
> +			break;
> +		if (descr[i] == '-')
> +			continue;
> +		report_local_descr[pos] = descr[i];
> +		if (pos + 1 == DESCR_SIZE)
> +			break;
> +		pos++;
> +	}
> +	report_local_descr[pos] = 0;
> +	return report_local_descr;
> +}
> +
> +void kmsan_print_origin(depot_stack_handle_t origin)
> +{
> +	unsigned long *entries = NULL, *chained_entries = NULL;
> +	unsigned int nr_entries, chained_nr_entries, skipnr;
> +	void *pc1 = NULL, *pc2 = NULL;
> +	depot_stack_handle_t head;
> +	unsigned long magic;
> +	char *descr = NULL;
> +
> +	if (!origin)
> +		return;
> +
> +	while (true) {
> +		nr_entries = stack_depot_fetch(origin, &entries);
> +		magic = nr_entries ? entries[0] : 0;
> +		if ((nr_entries == 4) && (magic == KMSAN_ALLOCA_MAGIC_ORIGIN)) {
> +			descr = (char *)entries[1];
> +			pc1 = (void *)entries[2];
> +			pc2 = (void *)entries[3];
> +			pr_err("Local variable %s created at:\n",
> +			       pretty_descr(descr));
> +			if (pc1)
> +				pr_err(" %pSb\n", pc1);
> +			if (pc2)
> +				pr_err(" %pSb\n", pc2);
> +			break;
> +		}
> +		if ((nr_entries == 3) && (magic == KMSAN_CHAIN_MAGIC_ORIGIN)) {
> +			head = entries[1];
> +			origin = entries[2];
> +			pr_err("Uninit was stored to memory at:\n");
> +			chained_nr_entries =
> +				stack_depot_fetch(head, &chained_entries);
> +			kmsan_internal_unpoison_memory(
> +				chained_entries,
> +				chained_nr_entries * sizeof(*chained_entries),
> +				/*checked*/ false);
> +			skipnr = get_stack_skipnr(chained_entries,
> +						  chained_nr_entries);
> +			stack_trace_print(chained_entries + skipnr,
> +					  chained_nr_entries - skipnr, 0);
> +			pr_err("\n");
> +			continue;
> +		}
> +		pr_err("Uninit was created at:\n");
> +		if (nr_entries) {
> +			skipnr = get_stack_skipnr(entries, nr_entries);
> +			stack_trace_print(entries + skipnr, nr_entries - skipnr,
> +					  0);
> +		} else {
> +			pr_err("(stack is not available)\n");
> +		}
> +		break;
> +	}
> +}
> +
> +void kmsan_report(depot_stack_handle_t origin, void *address, int size,
> +		  int off_first, int off_last, const void *user_addr,
> +		  enum kmsan_bug_reason reason)
> +{
> +	unsigned long stack_entries[KMSAN_STACK_DEPTH];
> +	int num_stack_entries, skipnr;
> +	char *bug_type = NULL;
> +	unsigned long flags, ua_flags;
> +	bool is_uaf;
> +
> +	if (!kmsan_enabled)
> +		return;
> +	if (!current->kmsan_ctx.allow_reporting)
> +		return;
> +	if (!origin)
> +		return;
> +
> +	current->kmsan_ctx.allow_reporting = false;
> +	ua_flags = user_access_save();
> +	spin_lock_irqsave(&kmsan_report_lock, flags);

I think this might want to be a raw_spin_lock, since the reporting can
be called from any context, including from within other raw_spin_lock'd
critical sections (practically this will only matter in RT kernels).

Also, do you have to do lockdep_off/on() (like kernel/kcsan/report.c
does, see comment there)?

> +	pr_err("=====================================================\n");
> +	is_uaf = kmsan_uaf_from_eb(stack_depot_get_extra_bits(origin));
> +	switch (reason) {
> +	case REASON_ANY:
> +		bug_type = is_uaf ? "use-after-free" : "uninit-value";
> +		break;
> +	case REASON_COPY_TO_USER:
> +		bug_type = is_uaf ? "kernel-infoleak-after-free" :
> +					  "kernel-infoleak";
> +		break;
> +	case REASON_SUBMIT_URB:
> +		bug_type = is_uaf ? "kernel-usb-infoleak-after-free" :
> +					  "kernel-usb-infoleak";
> +		break;
> +	}
> +
> +	num_stack_entries =
> +		stack_trace_save(stack_entries, KMSAN_STACK_DEPTH, 1);
> +	skipnr = get_stack_skipnr(stack_entries, num_stack_entries);
> +
> +	pr_err("BUG: KMSAN: %s in %pSb\n",
> +	       bug_type, (void *)stack_entries[skipnr]);
> +	stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
> +			  0);
> +	pr_err("\n");
> +
> +	kmsan_print_origin(origin);
> +
> +	if (size) {
> +		pr_err("\n");
> +		if (off_first == off_last)
> +			pr_err("Byte %d of %d is uninitialized\n", off_first,
> +			       size);
> +		else
> +			pr_err("Bytes %d-%d of %d are uninitialized\n",
> +			       off_first, off_last, size);
> +	}
> +	if (address)
> +		pr_err("Memory access of size %d starts at %px\n", size,
> +		       address);
> +	if (user_addr && reason == REASON_COPY_TO_USER)
> +		pr_err("Data copied to user address %px\n", user_addr);
> +	pr_err("\n");
> +	dump_stack_print_info(KERN_ERR);
> +	pr_err("=====================================================\n");
> +	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> +	spin_unlock_irqrestore(&kmsan_report_lock, flags);
> +	if (panic_on_kmsan)
> +		panic("kmsan.panic set ...\n");
> +	user_access_restore(ua_flags);
> +	current->kmsan_ctx.allow_reporting = true;
> +}
> diff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c
> new file mode 100644
> index 0000000000000..de58cfbc55b9d
> --- /dev/null
> +++ b/mm/kmsan/shadow.c
> @@ -0,0 +1,186 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KMSAN shadow implementation.
> + *
> + * Copyright (C) 2017-2022 Google LLC
> + * Author: Alexander Potapenko <glider@google.com>
> + *
> + */
> +
> +#include <asm/page.h>
> +#include <asm/pgtable_64_types.h>
> +#include <asm/tlbflush.h>
> +#include <linux/cacheflush.h>
> +#include <linux/memblock.h>
> +#include <linux/mm_types.h>
> +#include <linux/percpu-defs.h>
> +#include <linux/slab.h>
> +#include <linux/smp.h>
> +#include <linux/stddef.h>
> +
> +#include "../internal.h"
> +#include "kmsan.h"
> +
> +#define shadow_page_for(page) ((page)->kmsan_shadow)
> +
> +#define origin_page_for(page) ((page)->kmsan_origin)
> +
> +static void *shadow_ptr_for(struct page *page)
> +{
> +	return page_address(shadow_page_for(page));
> +}
> +
> +static void *origin_ptr_for(struct page *page)
> +{
> +	return page_address(origin_page_for(page));
> +}
> +
> +static bool page_has_metadata(struct page *page)
> +{
> +	return shadow_page_for(page) && origin_page_for(page);
> +}
> +
> +static void set_no_shadow_origin_page(struct page *page)
> +{
> +	shadow_page_for(page) = NULL;
> +	origin_page_for(page) = NULL;
> +}
> +
> +/*
> + * Dummy load and store pages to be used when the real metadata is unavailable.
> + * There are separate pages for loads and stores, so that every load returns a
> + * zero, and every store doesn't affect other loads.
> + */
> +static char dummy_load_page[PAGE_SIZE] __aligned(PAGE_SIZE);
> +static char dummy_store_page[PAGE_SIZE] __aligned(PAGE_SIZE);
> +
> +/*
> + * Taken from arch/x86/mm/physaddr.h to avoid using an instrumented version.
> + */
> +static int kmsan_phys_addr_valid(unsigned long addr)

int -> bool ? (it already deviates from the original by using IS_ENABLED
instead of #ifdef)

> +{
> +	if (IS_ENABLED(CONFIG_PHYS_ADDR_T_64BIT))
> +		return !(addr >> boot_cpu_data.x86_phys_bits);
> +	else
> +		return 1;
> +}
> +
> +/*
> + * Taken from arch/x86/mm/physaddr.c to avoid using an instrumented version.
> + */
> +static bool kmsan_virt_addr_valid(void *addr)
> +{
> +	unsigned long x = (unsigned long)addr;
> +	unsigned long y = x - __START_KERNEL_map;
> +
> +	/* use the carry flag to determine if x was < __START_KERNEL_map */
> +	if (unlikely(x > y)) {
> +		x = y + phys_base;
> +
> +		if (y >= KERNEL_IMAGE_SIZE)
> +			return false;
> +	} else {
> +		x = y + (__START_KERNEL_map - PAGE_OFFSET);
> +
> +		/* carry flag will be set if starting x was >= PAGE_OFFSET */
> +		if ((x > y) || !kmsan_phys_addr_valid(x))
> +			return false;
> +	}
> +
> +	return pfn_valid(x >> PAGE_SHIFT);
> +}

These seem quite x86-specific - to ease eventual porting to other
architectures, it would make sense to introduce <asm/kmsan.h> which will
have these 2 functions (and if there's anything else arch-specific like
this, moving to <asm/kmsan.h> would help eventual ports).

> +static unsigned long vmalloc_meta(void *addr, bool is_origin)
> +{
> +	unsigned long addr64 = (unsigned long)addr, off;
> +
> +	KMSAN_WARN_ON(is_origin && !IS_ALIGNED(addr64, KMSAN_ORIGIN_SIZE));
> +	if (kmsan_internal_is_vmalloc_addr(addr)) {
> +		off = addr64 - VMALLOC_START;
> +		return off + (is_origin ? KMSAN_VMALLOC_ORIGIN_START :
> +						KMSAN_VMALLOC_SHADOW_START);
> +	}
> +	if (kmsan_internal_is_module_addr(addr)) {
> +		off = addr64 - MODULES_VADDR;
> +		return off + (is_origin ? KMSAN_MODULES_ORIGIN_START :
> +						KMSAN_MODULES_SHADOW_START);
> +	}
> +	return 0;
> +}
> +
> +static struct page *virt_to_page_or_null(void *vaddr)
> +{
> +	if (kmsan_virt_addr_valid(vaddr))
> +		return virt_to_page(vaddr);
> +	else
> +		return NULL;
> +}
> +
> +struct shadow_origin_ptr kmsan_get_shadow_origin_ptr(void *address, u64 size,
> +						     bool store)
> +{
> +	struct shadow_origin_ptr ret;
> +	void *shadow;
> +
> +	/*
> +	 * Even if we redirect this memory access to the dummy page, it will
> +	 * go out of bounds.
> +	 */
> +	KMSAN_WARN_ON(size > PAGE_SIZE);
> +
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		goto return_dummy;
> +
> +	KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(address, size));
> +	shadow = kmsan_get_metadata(address, KMSAN_META_SHADOW);
> +	if (!shadow)
> +		goto return_dummy;
> +
> +	ret.shadow = shadow;
> +	ret.origin = kmsan_get_metadata(address, KMSAN_META_ORIGIN);
> +	return ret;
> +
> +return_dummy:
> +	if (store) {
> +		/* Ignore this store. */
> +		ret.shadow = dummy_store_page;
> +		ret.origin = dummy_store_page;
> +	} else {
> +		/* This load will return zero. */
> +		ret.shadow = dummy_load_page;
> +		ret.origin = dummy_load_page;
> +	}
> +	return ret;
> +}
> +
> +/*
> + * Obtain the shadow or origin pointer for the given address, or NULL if there's
> + * none. The caller must check the return value for being non-NULL if needed.
> + * The return value of this function should not depend on whether we're in the
> + * runtime or not.
> + */
> +void *kmsan_get_metadata(void *address, bool is_origin)
> +{
> +	u64 addr = (u64)address, pad, off;
> +	struct page *page;
> +	void *ret;
> +
> +	if (is_origin && !IS_ALIGNED(addr, KMSAN_ORIGIN_SIZE)) {
> +		pad = addr % KMSAN_ORIGIN_SIZE;
> +		addr -= pad;
> +	}
> +	address = (void *)addr;
> +	if (kmsan_internal_is_vmalloc_addr(address) ||
> +	    kmsan_internal_is_module_addr(address))
> +		return (void *)vmalloc_meta(address, is_origin);
> +
> +	page = virt_to_page_or_null(address);
> +	if (!page)
> +		return NULL;
> +	if (!page_has_metadata(page))
> +		return NULL;
> +	off = addr % PAGE_SIZE;
> +
> +	ret = (is_origin ? origin_ptr_for(page) : shadow_ptr_for(page)) + off;

Just return this and avoid 'ret'?

> +	return ret;
> +}
> diff --git a/scripts/Makefile.kmsan b/scripts/Makefile.kmsan
> new file mode 100644
> index 0000000000000..9793591f9855c
> --- /dev/null
> +++ b/scripts/Makefile.kmsan
> @@ -0,0 +1 @@

Makefile.kmsan needs SPDX-License-Identifier.

> +export CFLAGS_KMSAN := -fsanitize=kernel-memory
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 9f69ecdd7977a..49e6e57fdf4c8 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -157,6 +157,15 @@ _c_flags += $(if $(patsubst n%,, \
>  endif
>  endif
>  
> +ifeq ($(CONFIG_KMSAN),y)
> +_c_flags += $(if $(patsubst n%,, \
> +		$(KMSAN_SANITIZE_$(basetarget).o)$(KMSAN_SANITIZE)y), \
> +		$(CFLAGS_KMSAN))
> +_c_flags += $(if $(patsubst n%,, \
> +		$(KMSAN_ENABLE_CHECKS_$(basetarget).o)$(KMSAN_ENABLE_CHECKS)y), \
> +		, -mllvm -msan-disable-checks=1)
> +endif
> +
>  ifeq ($(CONFIG_UBSAN),y)
>  _c_flags += $(if $(patsubst n%,, \
>  		$(UBSAN_SANITIZE_$(basetarget).o)$(UBSAN_SANITIZE)$(CONFIG_UBSAN_SANITIZE_ALL)), \
> -- 
> 2.36.0.rc2.479.g8af0fa9b8e-goog
>