[PATCH v16 0/4] KASAN core changes for ppc64 radix KASAN

[PATCH v16 0/4] KASAN core changes for ppc64 radix KASAN

[Daniel Axtens]

Building on the work of Christophe, Aneesh and Balbir, I've ported
KASAN to 64-bit Book3S kernels running on the Radix MMU. I've been
trying this for a while, but we keep having collisions between the
kasan code in the mm tree and the code I want to put in to the ppc
tree.

This series just contains the kasan core changes that we need. These
can go in via the mm tree. I will then propose the powerpc changes for
a later cycle. (The most recent RFC for the powerpc changes is in the
v12 series at
https://lore.kernel.org/linux-mm/20210615014705.2234866-1-dja@axtens.net/
)

v16 applies to next-20210622. There should be no noticeable changes to
other platforms.

Changes since v15: Review comments from Andrey. Thanks Andrey.

Changes since v14: Included a bunch of Reviewed-by:s, thanks
Christophe and Marco. Cleaned up the build time error #ifdefs, thanks
Christophe.

Changes since v13: move the MAX_PTR_PER_* definitions out of kasan and
into pgtable.h. Add a build time error to hopefully prevent any
confusion about when the new hook is applicable. Thanks Marco and
Christophe.

Changes since v12: respond to Marco's review comments - clean up the
help for ARCH_DISABLE_KASAN_INLINE, and add an arch readiness check to
the new granule poisioning function. Thanks Marco.

Daniel Axtens (4):
  kasan: allow an architecture to disable inline instrumentation
  kasan: allow architectures to provide an outline readiness check
  mm: define default MAX_PTRS_PER_* in include/pgtable.h
  kasan: use MAX_PTRS_PER_* for early shadow tables

 arch/s390/include/asm/pgtable.h     |  2 --
 include/asm-generic/pgtable-nop4d.h |  1 -
 include/linux/kasan.h               |  6 +++---
 include/linux/pgtable.h             | 22 ++++++++++++++++++++++
 lib/Kconfig.kasan                   | 12 ++++++++++++
 mm/kasan/common.c                   |  3 +++
 mm/kasan/generic.c                  |  3 +++
 mm/kasan/init.c                     |  6 +++---
 mm/kasan/kasan.h                    |  6 ++++++
 mm/kasan/shadow.c                   |  6 ++++++
 10 files changed, 58 insertions(+), 9 deletions(-)

-- 
2.30.2

[PATCH v16 1/4] kasan: allow an architecture to disable inline instrumentation

[Daniel Axtens]

For annoying architectural reasons, it's very difficult to support inline
instrumentation on powerpc64.*

Add a Kconfig flag to allow an arch to disable inline. (It's a bit
annoying to be 'backwards', but I'm not aware of any way to have
an arch force a symbol to be 'n', rather than 'y'.)

We also disable stack instrumentation in this case as it does things that
are functionally equivalent to inline instrumentation, namely adding
code that touches the shadow directly without going through a C helper.

* on ppc64 atm, the shadow lives in virtual memory and isn't accessible in
real mode. However, before we turn on virtual memory, we parse the device
tree to determine which platform and MMU we're running under. That calls
generic DT code, which is instrumented. Inline instrumentation in DT would
unconditionally attempt to touch the shadow region, which we won't have
set up yet, and would crash. We can make outline mode wait for the arch to
be ready, but we can't change what the compiler inserts for inline mode.

Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 lib/Kconfig.kasan | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index cffc2ebbf185..c3b228828a80 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -12,6 +12,13 @@ config HAVE_ARCH_KASAN_HW_TAGS
 config HAVE_ARCH_KASAN_VMALLOC
 	bool
 
+config ARCH_DISABLE_KASAN_INLINE
+	bool
+	help
+	  An architecture might not support inline instrumentation.
+	  When this option is selected, inline and stack instrumentation are
+	  disabled.
+
 config CC_HAS_KASAN_GENERIC
 	def_bool $(cc-option, -fsanitize=kernel-address)
 
@@ -130,6 +137,7 @@ config KASAN_OUTLINE
 
 config KASAN_INLINE
 	bool "Inline instrumentation"
+	depends on !ARCH_DISABLE_KASAN_INLINE
 	help
 	  Compiler directly inserts code checking shadow memory before
 	  memory accesses. This is faster than outline (in some workloads
@@ -141,6 +149,7 @@ endchoice
 config KASAN_STACK
 	bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
 	depends on KASAN_GENERIC || KASAN_SW_TAGS
+	depends on !ARCH_DISABLE_KASAN_INLINE
 	default y if CC_IS_GCC
 	help
 	  The LLVM stack address sanitizer has a know problem that
@@ -154,6 +163,9 @@ config KASAN_STACK
 	  but clang users can still enable it for builds without
 	  CONFIG_COMPILE_TEST.	On gcc it is assumed to always be safe
 	  to use and enabled by default.
+	  If the architecture disables inline instrumentation, stack
+	  instrumentation is also disabled as it adds inline-style
+	  instrumentation that is run unconditionally.
 
 config KASAN_SW_TAGS_IDENTIFY
 	bool "Enable memory corruption identification"
-- 
2.30.2

[PATCH v16 2/4] kasan: allow architectures to provide an outline readiness check

[Daniel Axtens]

Allow architectures to define a kasan_arch_is_ready() hook that bails
out of any function that's about to touch the shadow unless the arch
says that it is ready for the memory to be accessed. This is fairly
uninvasive and should have a negligible performance penalty.

This will only work in outline mode, so an arch must specify
ARCH_DISABLE_KASAN_INLINE if it requires this.

Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>

--

Both previous RFCs for ppc64 - by 2 different people - have
needed this trick! See:
 - https://lore.kernel.org/patchwork/patch/592820/ # ppc64 hash series
 - https://patchwork.ozlabs.org/patch/795211/      # ppc radix series

Build tested on arm64 with SW_TAGS and x86 with INLINE: the error fires
if I add a kasan_arch_is_ready define.
---
 mm/kasan/common.c  | 3 +++
 mm/kasan/generic.c | 3 +++
 mm/kasan/kasan.h   | 6 ++++++
 mm/kasan/shadow.c  | 6 ++++++
 4 files changed, 18 insertions(+)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 10177cc26d06..2baf121fb8c5 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -331,6 +331,9 @@ static inline bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
 	u8 tag;
 	void *tagged_object;
 
+	if (!kasan_arch_is_ready())
+		return false;
+
 	tag = get_tag(object);
 	tagged_object = object;
 	object = kasan_reset_tag(object);
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 53cbf28859b5..c3f5ba7a294a 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -163,6 +163,9 @@ static __always_inline bool check_region_inline(unsigned long addr,
 						size_t size, bool write,
 						unsigned long ret_ip)
 {
+	if (!kasan_arch_is_ready())
+		return true;
+
 	if (unlikely(size == 0))
 		return true;
 
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 8f450bc28045..4dbc8def64f4 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -449,6 +449,12 @@ static inline void kasan_poison_last_granule(const void *address, size_t size) {
 
 #endif /* CONFIG_KASAN_GENERIC */
 
+#ifndef kasan_arch_is_ready
+static inline bool kasan_arch_is_ready(void)	{ return true; }
+#elif !defined(CONFIG_KASAN_GENERIC) || !defined(CONFIG_KASAN_OUTLINE)
+#error kasan_arch_is_ready only works in KASAN generic outline mode!
+#endif
+
 /*
  * Exported functions for interfaces called from assembly or from generated
  * code. Declarations here to avoid warning about missing declarations.
diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
index 082ee5b6d9a1..8d95ee52d019 100644
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -73,6 +73,9 @@ void kasan_poison(const void *addr, size_t size, u8 value, bool init)
 {
 	void *shadow_start, *shadow_end;
 
+	if (!kasan_arch_is_ready())
+		return;
+
 	/*
 	 * Perform shadow offset calculation based on untagged address, as
 	 * some of the callers (e.g. kasan_poison_object_data) pass tagged
@@ -99,6 +102,9 @@ EXPORT_SYMBOL(kasan_poison);
 #ifdef CONFIG_KASAN_GENERIC
 void kasan_poison_last_granule(const void *addr, size_t size)
 {
+	if (!kasan_arch_is_ready())
+		return;
+
 	if (size & KASAN_GRANULE_MASK) {
 		u8 *shadow = (u8 *)kasan_mem_to_shadow(addr + size);
 		*shadow = size & KASAN_GRANULE_MASK;
-- 
2.30.2

[PATCH v16 3/4] mm: define default MAX_PTRS_PER_* in include/pgtable.h

[Daniel Axtens]

Commit c65e774fb3f6 ("x86/mm: Make PGDIR_SHIFT and PTRS_PER_P4D variable")
made PTRS_PER_P4D variable on x86 and introduced MAX_PTRS_PER_P4D as a
constant for cases which need a compile-time constant (e.g. fixed-size
arrays).

powerpc likewise has boot-time selectable MMU features which can cause
other mm "constants" to vary. For KASAN, we have some static
PTE/PMD/PUD/P4D arrays so we need compile-time maximums for all these
constants. Extend the MAX_PTRS_PER_ idiom, and place default definitions
in include/pgtable.h. These define MAX_PTRS_PER_x to be PTRS_PER_x unless
an architecture has defined MAX_PTRS_PER_x in its arch headers.

Clean up pgtable-nop4d.h and s390's MAX_PTRS_PER_P4D definitions while
we're at it: both can just pick up the default now.

Acked-by: Andrey Konovalov <andreyknvl@gmail.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>

---

s390 was compile tested only.
---
 arch/s390/include/asm/pgtable.h     |  2 --
 include/asm-generic/pgtable-nop4d.h |  1 -
 include/linux/pgtable.h             | 22 ++++++++++++++++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 79742f497cb5..dcac7b2df72c 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -343,8 +343,6 @@ static inline int is_module_addr(void *addr)
 #define PTRS_PER_P4D	_CRST_ENTRIES
 #define PTRS_PER_PGD	_CRST_ENTRIES
 
-#define MAX_PTRS_PER_P4D	PTRS_PER_P4D
-
 /*
  * Segment table and region3 table entry encoding
  * (R = read-only, I = invalid, y = young bit):
diff --git a/include/asm-generic/pgtable-nop4d.h b/include/asm-generic/pgtable-nop4d.h
index 2f1d0aad645c..03b7dae47dd4 100644
--- a/include/asm-generic/pgtable-nop4d.h
+++ b/include/asm-generic/pgtable-nop4d.h
@@ -9,7 +9,6 @@
 typedef struct { pgd_t pgd; } p4d_t;
 
 #define P4D_SHIFT		PGDIR_SHIFT
-#define MAX_PTRS_PER_P4D	1
 #define PTRS_PER_P4D		1
 #define P4D_SIZE		(1UL << P4D_SHIFT)
 #define P4D_MASK		(~(P4D_SIZE-1))
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index fb20c57de2ce..d147480cdefc 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1634,4 +1634,26 @@ typedef unsigned int pgtbl_mod_mask;
 #define pte_leaf_size(x) PAGE_SIZE
 #endif
 
+/*
+ * Some architectures have MMUs that are configurable or selectable at boot
+ * time. These lead to variable PTRS_PER_x. For statically allocated arrays it
+ * helps to have a static maximum value.
+ */
+
+#ifndef MAX_PTRS_PER_PTE
+#define MAX_PTRS_PER_PTE PTRS_PER_PTE
+#endif
+
+#ifndef MAX_PTRS_PER_PMD
+#define MAX_PTRS_PER_PMD PTRS_PER_PMD
+#endif
+
+#ifndef MAX_PTRS_PER_PUD
+#define MAX_PTRS_PER_PUD PTRS_PER_PUD
+#endif
+
+#ifndef MAX_PTRS_PER_P4D
+#define MAX_PTRS_PER_P4D PTRS_PER_P4D
+#endif
+
 #endif /* _LINUX_PGTABLE_H */
-- 
2.30.2

[PATCH v16 4/4] kasan: use MAX_PTRS_PER_* for early shadow tables

[Daniel Axtens]

powerpc has a variable number of PTRS_PER_*, set at runtime based
on the MMU that the kernel is booted under.

This means the PTRS_PER_* are no longer constants, and therefore
breaks the build. Switch to using MAX_PTRS_PER_*, which are constant.

Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Suggested-by: Balbir Singh <bsingharora@gmail.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Balbir Singh <bsingharora@gmail.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 include/linux/kasan.h | 6 +++---
 mm/kasan/init.c       | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 768d7d342757..5310e217bd74 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -41,9 +41,9 @@ struct kunit_kasan_expectation {
 #endif
 
 extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
-extern pte_t kasan_early_shadow_pte[PTRS_PER_PTE + PTE_HWTABLE_PTRS];
-extern pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD];
-extern pud_t kasan_early_shadow_pud[PTRS_PER_PUD];
+extern pte_t kasan_early_shadow_pte[MAX_PTRS_PER_PTE + PTE_HWTABLE_PTRS];
+extern pmd_t kasan_early_shadow_pmd[MAX_PTRS_PER_PMD];
+extern pud_t kasan_early_shadow_pud[MAX_PTRS_PER_PUD];
 extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
 
 int kasan_populate_early_shadow(const void *shadow_start,
diff --git a/mm/kasan/init.c b/mm/kasan/init.c
index 348f31d15a97..cc64ed6858c6 100644
--- a/mm/kasan/init.c
+++ b/mm/kasan/init.c
@@ -41,7 +41,7 @@ static inline bool kasan_p4d_table(pgd_t pgd)
 }
 #endif
 #if CONFIG_PGTABLE_LEVELS > 3
-pud_t kasan_early_shadow_pud[PTRS_PER_PUD] __page_aligned_bss;
+pud_t kasan_early_shadow_pud[MAX_PTRS_PER_PUD] __page_aligned_bss;
 static inline bool kasan_pud_table(p4d_t p4d)
 {
 	return p4d_page(p4d) == virt_to_page(lm_alias(kasan_early_shadow_pud));
@@ -53,7 +53,7 @@ static inline bool kasan_pud_table(p4d_t p4d)
 }
 #endif
 #if CONFIG_PGTABLE_LEVELS > 2
-pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD] __page_aligned_bss;
+pmd_t kasan_early_shadow_pmd[MAX_PTRS_PER_PMD] __page_aligned_bss;
 static inline bool kasan_pmd_table(pud_t pud)
 {
 	return pud_page(pud) == virt_to_page(lm_alias(kasan_early_shadow_pmd));
@@ -64,7 +64,7 @@ static inline bool kasan_pmd_table(pud_t pud)
 	return false;
 }
 #endif
-pte_t kasan_early_shadow_pte[PTRS_PER_PTE + PTE_HWTABLE_PTRS]
+pte_t kasan_early_shadow_pte[MAX_PTRS_PER_PTE + PTE_HWTABLE_PTRS]
 	__page_aligned_bss;
 
 static inline bool kasan_pte_table(pmd_t pmd)
-- 
2.30.2

Re: [PATCH v16 1/4] kasan: allow an architecture to disable inline instrumentation

[Andrey Konovalov]

On Thu, Jun 24, 2021 at 6:41 AM Daniel Axtens <dja@axtens.net> wrote:
>
> For annoying architectural reasons, it's very difficult to support inline
> instrumentation on powerpc64.*
>
> Add a Kconfig flag to allow an arch to disable inline. (It's a bit
> annoying to be 'backwards', but I'm not aware of any way to have
> an arch force a symbol to be 'n', rather than 'y'.)
>
> We also disable stack instrumentation in this case as it does things that
> are functionally equivalent to inline instrumentation, namely adding
> code that touches the shadow directly without going through a C helper.
>
> * on ppc64 atm, the shadow lives in virtual memory and isn't accessible in
> real mode. However, before we turn on virtual memory, we parse the device
> tree to determine which platform and MMU we're running under. That calls
> generic DT code, which is instrumented. Inline instrumentation in DT would
> unconditionally attempt to touch the shadow region, which we won't have
> set up yet, and would crash. We can make outline mode wait for the arch to
> be ready, but we can't change what the compiler inserts for inline mode.
>
> Reviewed-by: Marco Elver <elver@google.com>
> Signed-off-by: Daniel Axtens <dja@axtens.net>
> ---
>  lib/Kconfig.kasan | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index cffc2ebbf185..c3b228828a80 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -12,6 +12,13 @@ config HAVE_ARCH_KASAN_HW_TAGS
>  config HAVE_ARCH_KASAN_VMALLOC
>         bool
>
> +config ARCH_DISABLE_KASAN_INLINE
> +       bool
> +       help
> +         An architecture might not support inline instrumentation.
> +         When this option is selected, inline and stack instrumentation are
> +         disabled.
> +
>  config CC_HAS_KASAN_GENERIC
>         def_bool $(cc-option, -fsanitize=kernel-address)
>
> @@ -130,6 +137,7 @@ config KASAN_OUTLINE
>
>  config KASAN_INLINE
>         bool "Inline instrumentation"
> +       depends on !ARCH_DISABLE_KASAN_INLINE
>         help
>           Compiler directly inserts code checking shadow memory before
>           memory accesses. This is faster than outline (in some workloads
> @@ -141,6 +149,7 @@ endchoice
>  config KASAN_STACK
>         bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
>         depends on KASAN_GENERIC || KASAN_SW_TAGS
> +       depends on !ARCH_DISABLE_KASAN_INLINE
>         default y if CC_IS_GCC
>         help
>           The LLVM stack address sanitizer has a know problem that
> @@ -154,6 +163,9 @@ config KASAN_STACK
>           but clang users can still enable it for builds without
>           CONFIG_COMPILE_TEST.  On gcc it is assumed to always be safe
>           to use and enabled by default.
> +         If the architecture disables inline instrumentation, stack
> +         instrumentation is also disabled as it adds inline-style
> +         instrumentation that is run unconditionally.
>
>  config KASAN_SW_TAGS_IDENTIFY
>         bool "Enable memory corruption identification"
> --
> 2.30.2
>

Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>

Thanks, Daniel!

Re: [PATCH v16 2/4] kasan: allow architectures to provide an outline readiness check

[Andrey Konovalov]

On Thu, Jun 24, 2021 at 6:41 AM Daniel Axtens <dja@axtens.net> wrote:
>
> Allow architectures to define a kasan_arch_is_ready() hook that bails
> out of any function that's about to touch the shadow unless the arch
> says that it is ready for the memory to be accessed. This is fairly
> uninvasive and should have a negligible performance penalty.
>
> This will only work in outline mode, so an arch must specify
> ARCH_DISABLE_KASAN_INLINE if it requires this.
>
> Cc: Balbir Singh <bsingharora@gmail.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> Reviewed-by: Marco Elver <elver@google.com>
> Signed-off-by: Daniel Axtens <dja@axtens.net>
>
> --
>
> Both previous RFCs for ppc64 - by 2 different people - have
> needed this trick! See:
>  - https://lore.kernel.org/patchwork/patch/592820/ # ppc64 hash series
>  - https://patchwork.ozlabs.org/patch/795211/      # ppc radix series
>
> Build tested on arm64 with SW_TAGS and x86 with INLINE: the error fires
> if I add a kasan_arch_is_ready define.
> ---
>  mm/kasan/common.c  | 3 +++
>  mm/kasan/generic.c | 3 +++
>  mm/kasan/kasan.h   | 6 ++++++
>  mm/kasan/shadow.c  | 6 ++++++
>  4 files changed, 18 insertions(+)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 10177cc26d06..2baf121fb8c5 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -331,6 +331,9 @@ static inline bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
>         u8 tag;
>         void *tagged_object;
>
> +       if (!kasan_arch_is_ready())
> +               return false;
> +
>         tag = get_tag(object);
>         tagged_object = object;
>         object = kasan_reset_tag(object);
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index 53cbf28859b5..c3f5ba7a294a 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -163,6 +163,9 @@ static __always_inline bool check_region_inline(unsigned long addr,
>                                                 size_t size, bool write,
>                                                 unsigned long ret_ip)
>  {
> +       if (!kasan_arch_is_ready())
> +               return true;
> +
>         if (unlikely(size == 0))
>                 return true;
>
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 8f450bc28045..4dbc8def64f4 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -449,6 +449,12 @@ static inline void kasan_poison_last_granule(const void *address, size_t size) {
>
>  #endif /* CONFIG_KASAN_GENERIC */
>
> +#ifndef kasan_arch_is_ready
> +static inline bool kasan_arch_is_ready(void)   { return true; }
> +#elif !defined(CONFIG_KASAN_GENERIC) || !defined(CONFIG_KASAN_OUTLINE)
> +#error kasan_arch_is_ready only works in KASAN generic outline mode!
> +#endif
> +
>  /*
>   * Exported functions for interfaces called from assembly or from generated
>   * code. Declarations here to avoid warning about missing declarations.
> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index 082ee5b6d9a1..8d95ee52d019 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -73,6 +73,9 @@ void kasan_poison(const void *addr, size_t size, u8 value, bool init)
>  {
>         void *shadow_start, *shadow_end;
>
> +       if (!kasan_arch_is_ready())
> +               return;
> +
>         /*
>          * Perform shadow offset calculation based on untagged address, as
>          * some of the callers (e.g. kasan_poison_object_data) pass tagged
> @@ -99,6 +102,9 @@ EXPORT_SYMBOL(kasan_poison);
>  #ifdef CONFIG_KASAN_GENERIC
>  void kasan_poison_last_granule(const void *addr, size_t size)
>  {
> +       if (!kasan_arch_is_ready())
> +               return;
> +
>         if (size & KASAN_GRANULE_MASK) {
>                 u8 *shadow = (u8 *)kasan_mem_to_shadow(addr + size);
>                 *shadow = size & KASAN_GRANULE_MASK;
> --
> 2.30.2
>

Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>