[PATCH v12 0/6] KASAN core changes for ppc64 radix KASAN

[PATCH v12 0/6] 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. So my aim here is for patches 1 through 4 or 1 through 5
to go in via the mm tree. I will then propose the powerpc changes for
a later cycle. (I have attached them to this series as an RFC, and
there are still outstanding review comments I need to attend to.)

v12 applies to next-20210611. There should be no noticable changes to
other platforms.

Kind regards,
Daniel

Daniel Axtens (6):
  kasan: allow an architecture to disable inline instrumentation
  kasan: allow architectures to provide an outline readiness check
  kasan: define and use MAX_PTRS_PER_* for early shadow tables
  kasan: Document support on 32-bit powerpc
  powerpc/mm/kasan: rename kasan_init_32.c to init_32.c
  [RFC] powerpc: Book3S 64-bit outline-only KASAN support

 Documentation/dev-tools/kasan.rst             |  7 +-
 Documentation/powerpc/kasan.txt               | 58 +++++++++++
 arch/powerpc/Kconfig                          |  4 +-
 arch/powerpc/Kconfig.debug                    |  3 +-
 arch/powerpc/include/asm/book3s/64/hash.h     |  4 +
 arch/powerpc/include/asm/book3s/64/pgtable.h  |  4 +
 arch/powerpc/include/asm/book3s/64/radix.h    | 13 ++-
 arch/powerpc/include/asm/kasan.h              | 22 +++++
 arch/powerpc/kernel/Makefile                  | 11 +++
 arch/powerpc/kernel/process.c                 | 16 ++--
 arch/powerpc/kvm/Makefile                     |  5 +
 arch/powerpc/mm/book3s64/Makefile             |  9 ++
 arch/powerpc/mm/kasan/Makefile                |  3 +-
 .../mm/kasan/{kasan_init_32.c => init_32.c}   |  0
 arch/powerpc/mm/kasan/init_book3s_64.c        | 95 +++++++++++++++++++
 arch/powerpc/mm/ptdump/ptdump.c               | 20 +++-
 arch/powerpc/platforms/Kconfig.cputype        |  1 +
 arch/powerpc/platforms/powernv/Makefile       |  6 ++
 arch/powerpc/platforms/pseries/Makefile       |  3 +
 include/linux/kasan.h                         | 18 +++-
 lib/Kconfig.kasan                             | 14 +++
 mm/kasan/common.c                             |  4 +
 mm/kasan/generic.c                            |  3 +
 mm/kasan/init.c                               |  6 +-
 mm/kasan/kasan.h                              |  4 +
 mm/kasan/shadow.c                             |  4 +
 26 files changed, 316 insertions(+), 21 deletions(-)
 create mode 100644 Documentation/powerpc/kasan.txt
 rename arch/powerpc/mm/kasan/{kasan_init_32.c => init_32.c} (100%)
 create mode 100644 arch/powerpc/mm/kasan/init_book3s_64.c

-- 
2.27.0

[PATCH v12 1/6] 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.

Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 lib/Kconfig.kasan | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index cffc2ebbf185..935814f332a7 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -12,6 +12,15 @@ config HAVE_ARCH_KASAN_HW_TAGS
 config HAVE_ARCH_KASAN_VMALLOC
 	bool
 
+# Sometimes an architecture might not be able to support inline instrumentation
+# but might be able to support outline instrumentation. This option allows an 
+# arch to prevent inline and stack instrumentation from being enabled.
+# ppc64 turns on virtual memory late in boot, after calling into generic code
+# like the device-tree parser, so it uses this in conjuntion with a hook in
+# outline mode to avoid invalid access early in boot.
+config ARCH_DISABLE_KASAN_INLINE
+	bool
+
 config CC_HAS_KASAN_GENERIC
 	def_bool $(cc-option, -fsanitize=kernel-address)
 
@@ -130,6 +139,7 @@ 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 +151,7 @@ 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 +165,9 @@ 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, this is
+	  also disabled as it adds inline-style instrumentation that
+	  is run unconditionally.
 
 config KASAN_SW_TAGS_IDENTIFY
 	bool "Enable memory corruption identification"
-- 
2.27.0

[PATCH v12 2/6] 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.vnet.ibm.com>
Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Daniel Axtens <dja@axtens.net>

--

I discuss the justfication for this later in the series. Also,
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
---
 mm/kasan/common.c  | 4 ++++
 mm/kasan/generic.c | 3 +++
 mm/kasan/kasan.h   | 4 ++++
 mm/kasan/shadow.c  | 4 ++++
 4 files changed, 15 insertions(+)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 10177cc26d06..0ad615f3801d 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -331,6 +331,10 @@ static inline bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
 	u8 tag;
 	void *tagged_object;
 
+	/* Bail if the arch isn't ready */
+	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..19323a3d5975 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -449,6 +449,10 @@ 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; }
+#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..74134b657d7d 100644
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -73,6 +73,10 @@ void kasan_poison(const void *addr, size_t size, u8 value, bool init)
 {
 	void *shadow_start, *shadow_end;
 
+	/* Don't touch the shadow memory if arch isn't ready */
+	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
-- 
2.27.0

[PATCH v12 3/6] kasan: define and 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.

Define default MAX_PTRS_PER_*s in the same style as MAX_PTRS_PER_P4D.
As KASAN is the only user at the moment, just define them in the kasan
header, and have them default to PTRS_PER_* unless overridden in arch
code.

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>
Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 include/linux/kasan.h | 18 +++++++++++++++---
 mm/kasan/init.c       |  6 +++---
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 768d7d342757..fd65f477ac92 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -40,10 +40,22 @@ struct kunit_kasan_expectation {
 #define PTE_HWTABLE_PTRS 0
 #endif
 
+#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
+
 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)
-- 
2.27.0

[PATCH v12 4/6] kasan: Document support on 32-bit powerpc

[Daniel Axtens]

KASAN is supported on 32-bit powerpc and the docs should reflect this.

Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 Documentation/dev-tools/kasan.rst |  8 ++++++--
 Documentation/powerpc/kasan.txt   | 12 ++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/powerpc/kasan.txt

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index 83ec4a556c19..05d2d428a332 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -36,7 +36,8 @@ Both software KASAN modes work with SLUB and SLAB memory allocators,
 while the hardware tag-based KASAN currently only supports SLUB.
 
 Currently, generic KASAN is supported for the x86_64, arm, arm64, xtensa, s390,
-and riscv architectures, and tag-based KASAN modes are supported only for arm64.
+and riscv architectures. It is also supported on 32-bit powerpc kernels.
+Tag-based KASAN modes are supported only for arm64.
 
 Usage
 -----
@@ -343,7 +344,10 @@ CONFIG_KASAN_VMALLOC
 
 With ``CONFIG_KASAN_VMALLOC``, KASAN can cover vmalloc space at the
 cost of greater memory usage. Currently, this is supported on x86,
-riscv, s390, and powerpc.
+riscv, s390, and 32-bit powerpc.
+
+It is optional, except on 32-bit powerpc kernels with module support,
+where it is required.
 
 This works by hooking into vmalloc and vmap and dynamically
 allocating real shadow memory to back the mappings.
diff --git a/Documentation/powerpc/kasan.txt b/Documentation/powerpc/kasan.txt
new file mode 100644
index 000000000000..26bb0e8bb18c
--- /dev/null
+++ b/Documentation/powerpc/kasan.txt
@@ -0,0 +1,12 @@
+KASAN is supported on powerpc on 32-bit only.
+
+32 bit support
+==============
+
+KASAN is supported on both hash and nohash MMUs on 32-bit.
+
+The shadow area sits at the top of the kernel virtual memory space above the
+fixmap area and occupies one eighth of the total kernel virtual memory space.
+
+Instrumentation of the vmalloc area is optional, unless built with modules,
+in which case it is required.
-- 
2.27.0

[PATCH v12 5/6] powerpc/mm/kasan: rename kasan_init_32.c to init_32.c

[Daniel Axtens]

kasan is already implied by the directory name, we don't need to
repeat it.

Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 arch/powerpc/mm/kasan/Makefile                       | 2 +-
 arch/powerpc/mm/kasan/{kasan_init_32.c => init_32.c} | 0
 2 files changed, 1 insertion(+), 1 deletion(-)
 rename arch/powerpc/mm/kasan/{kasan_init_32.c => init_32.c} (100%)

diff --git a/arch/powerpc/mm/kasan/Makefile b/arch/powerpc/mm/kasan/Makefile
index bb1a5408b86b..42fb628a44fd 100644
--- a/arch/powerpc/mm/kasan/Makefile
+++ b/arch/powerpc/mm/kasan/Makefile
@@ -2,6 +2,6 @@
 
 KASAN_SANITIZE := n
 
-obj-$(CONFIG_PPC32)           += kasan_init_32.o
+obj-$(CONFIG_PPC32)           += init_32.o
 obj-$(CONFIG_PPC_8xx)		+= 8xx.o
 obj-$(CONFIG_PPC_BOOK3S_32)	+= book3s_32.o
diff --git a/arch/powerpc/mm/kasan/kasan_init_32.c b/arch/powerpc/mm/kasan/init_32.c
similarity index 100%
rename from arch/powerpc/mm/kasan/kasan_init_32.c
rename to arch/powerpc/mm/kasan/init_32.c
-- 
2.27.0

[PATCH v12 6/6] [RFC] powerpc: Book3S 64-bit outline-only KASAN support

[Daniel Axtens]

[I'm hoping to get this in a subsequent merge window after we get the core
changes in. I know there are still a few outstanding review comments, I just
wanted to make sure that I supplied a real use-case for the core changes I'm
proposing.]

Implement a limited form of KASAN for Book3S 64-bit machines running under
the Radix MMU, supporting only outline mode.

 - Enable the compiler instrumentation to check addresses and maintain the
   shadow region. (This is the guts of KASAN which we can easily reuse.)

 - Require kasan-vmalloc support to handle modules and anything else in
   vmalloc space.

 - KASAN needs to be able to validate all pointer accesses, but we can't
   instrument all kernel addresses - only linear map and vmalloc. On boot,
   set up a single page of read-only shadow that marks all iomap and
   vmemmap accesses as valid.

 - Document KASAN in both generic and powerpc docs.

Background
----------

KASAN support on Book3S is a bit tricky to get right:

 - It would be good to support inline instrumentation so as to be able to
   catch stack issues that cannot be caught with outline mode.

 - Inline instrumentation requires a fixed offset.

 - Book3S runs code with translations off ("real mode") during boot,
   including a lot of generic device-tree parsing code which is used to
   determine MMU features.

    [ppc64 mm note: The kernel installs a linear mapping at effective
    address c000...-c008.... This is a one-to-one mapping with physical
    memory from 0000... onward. Because of how memory accesses work on
    powerpc 64-bit Book3S, a kernel pointer in the linear map accesses the
    same memory both with translations on (accessing as an 'effective
    address'), and with translations off (accessing as a 'real
    address'). This works in both guests and the hypervisor. For more
    details, see s5.7 of Book III of version 3 of the ISA, in particular
    the Storage Control Overview, s5.7.3, and s5.7.5 - noting that this
    KASAN implementation currently only supports Radix.]

 - Some code - most notably a lot of KVM code - also runs with translations
   off after boot.

 - Therefore any offset has to point to memory that is valid with
   translations on or off.

One approach is just to give up on inline instrumentation. This way
boot-time checks can be delayed until after the MMU is set is up, and we
can just not instrument any code that runs with translations off after
booting. Take this approach for now and require outline instrumentation.

Previous attempts allowed inline instrumentation. However, they came with
some unfortunate restrictions: only physically contiguous memory could be
used and it had to be specified at compile time. Maybe we can do better in
the future.

Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> # ppc64 hash version
Cc: Christophe Leroy <christophe.leroy@csgroup.eu> # ppc32 version
Originally-by: Balbir Singh <bsingharora@gmail.com> # ppc64 out-of-line radix version
Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 Documentation/dev-tools/kasan.rst            | 11 +--
 Documentation/powerpc/kasan.txt              | 48 +++++++++-
 arch/powerpc/Kconfig                         |  4 +-
 arch/powerpc/Kconfig.debug                   |  3 +-
 arch/powerpc/include/asm/book3s/64/hash.h    |  4 +
 arch/powerpc/include/asm/book3s/64/pgtable.h |  4 +
 arch/powerpc/include/asm/book3s/64/radix.h   | 13 ++-
 arch/powerpc/include/asm/kasan.h             | 22 +++++
 arch/powerpc/kernel/Makefile                 | 11 +++
 arch/powerpc/kernel/process.c                | 16 ++--
 arch/powerpc/kvm/Makefile                    |  5 ++
 arch/powerpc/mm/book3s64/Makefile            |  9 ++
 arch/powerpc/mm/kasan/Makefile               |  1 +
 arch/powerpc/mm/kasan/init_book3s_64.c       | 95 ++++++++++++++++++++
 arch/powerpc/mm/ptdump/ptdump.c              | 20 ++++-
 arch/powerpc/platforms/Kconfig.cputype       |  1 +
 arch/powerpc/platforms/powernv/Makefile      |  6 ++
 arch/powerpc/platforms/pseries/Makefile      |  3 +
 18 files changed, 257 insertions(+), 19 deletions(-)
 create mode 100644 arch/powerpc/mm/kasan/init_book3s_64.c

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index 05d2d428a332..f8d6048db1bb 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -36,8 +36,9 @@ Both software KASAN modes work with SLUB and SLAB memory allocators,
 while the hardware tag-based KASAN currently only supports SLUB.
 
 Currently, generic KASAN is supported for the x86_64, arm, arm64, xtensa, s390,
-and riscv architectures. It is also supported on 32-bit powerpc kernels.
-Tag-based KASAN modes are supported only for arm64.
+and riscv architectures. It is also supported on powerpc for 32-bit kernels and
+for 64-bit kernels running under the Radix MMU. Tag-based KASAN modes are
+supported only for arm64.
 
 Usage
 -----
@@ -344,10 +345,10 @@ CONFIG_KASAN_VMALLOC
 
 With ``CONFIG_KASAN_VMALLOC``, KASAN can cover vmalloc space at the
 cost of greater memory usage. Currently, this is supported on x86,
-riscv, s390, and 32-bit powerpc.
+riscv, s390, and powerpc.
 
-It is optional, except on 32-bit powerpc kernels with module support,
-where it is required.
+It is optional, except on 64-bit powerpc kernels, and on 32-bit
+powerpc kernels with module support, where it is required.
 
 This works by hooking into vmalloc and vmap and dynamically
 allocating real shadow memory to back the mappings.
diff --git a/Documentation/powerpc/kasan.txt b/Documentation/powerpc/kasan.txt
index 26bb0e8bb18c..f032b4eaf205 100644
--- a/Documentation/powerpc/kasan.txt
+++ b/Documentation/powerpc/kasan.txt
@@ -1,4 +1,4 @@
-KASAN is supported on powerpc on 32-bit only.
+KASAN is supported on powerpc on 32-bit and Radix 64-bit only.
 
 32 bit support
 ==============
@@ -10,3 +10,49 @@ fixmap area and occupies one eighth of the total kernel virtual memory space.
 
 Instrumentation of the vmalloc area is optional, unless built with modules,
 in which case it is required.
+
+64 bit support
+==============
+
+Currently, only the radix MMU is supported. There have been versions for hash
+and Book3E processors floating around on the mailing list, but nothing has been
+merged.
+
+KASAN support on Book3S is a bit tricky to get right:
+
+ - It would be good to support inline instrumentation so as to be able to catch
+   stack issues that cannot be caught with outline mode.
+
+ - Inline instrumentation requires a fixed offset.
+
+ - Book3S runs code with translations off ("real mode") during boot, including a
+   lot of generic device-tree parsing code which is used to determine MMU
+   features.
+
+ - Some code - most notably a lot of KVM code - also runs with translations off
+   after boot.
+
+ - Therefore any offset has to point to memory that is valid with
+   translations on or off.
+
+One approach is just to give up on inline instrumentation. This way boot-time
+checks can be delayed until after the MMU is set is up, and we can just not
+instrument any code that runs with translations off after booting. This is the
+current approach.
+
+To avoid this limitiation, the KASAN shadow would have to be placed inside the
+linear mapping, using the same high-bits trick we use for the rest of the linear
+mapping. This is tricky:
+
+ - We'd like to place it near the start of physical memory. In theory we can do
+   this at run-time based on how much physical memory we have, but this requires
+   being able to arbitrarily relocate the kernel, which is basically the tricky
+   part of KASLR. Not being game to implement both tricky things at once, this
+   is hopefully something we can revisit once we get KASLR for Book3S.
+
+ - Alternatively, we can place the shadow at the _end_ of memory, but this
+   requires knowing how much contiguous physical memory a system has _at compile
+   time_. This is a big hammer, and has some unfortunate consequences: inablity
+   to handle discontiguous physical memory, total failure to boot on machines
+   with less memory than specified, and that machines with more memory than
+   specified can't use it. This was deemed unacceptable.
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index dbccb0676e48..ff16af7022b1 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -118,6 +118,7 @@ config PPC
 	# Please keep this list sorted alphabetically.
 	#
 	select ARCH_32BIT_OFF_T if PPC32
+	select ARCH_DISABLE_KASAN_INLINE	if PPC_RADIX_MMU
 	select ARCH_ENABLE_MEMORY_HOTPLUG
 	select ARCH_ENABLE_MEMORY_HOTREMOVE
 	select ARCH_HAS_COPY_MC			if PPC64
@@ -191,7 +192,8 @@ config PPC
 	select HAVE_ARCH_JUMP_LABEL
 	select HAVE_ARCH_JUMP_LABEL_RELATIVE
 	select HAVE_ARCH_KASAN			if PPC32 && PPC_PAGE_SHIFT <= 14
-	select HAVE_ARCH_KASAN_VMALLOC		if PPC32 && PPC_PAGE_SHIFT <= 14
+	select HAVE_ARCH_KASAN			if PPC_RADIX_MMU
+	select HAVE_ARCH_KASAN_VMALLOC		if HAVE_ARCH_KASAN
 	select HAVE_ARCH_KFENCE			if PPC32
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_MMAP_RND_BITS
diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 6342f9da4545..ad5b776a96e7 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -399,4 +399,5 @@ config PPC_FAST_ENDIAN_SWITCH
 config KASAN_SHADOW_OFFSET
 	hex
 	depends on KASAN
-	default 0xe0000000
+	default 0xe0000000 if PPC32
+	default 0xa80e000000000000 if PPC64
diff --git a/arch/powerpc/include/asm/book3s/64/hash.h b/arch/powerpc/include/asm/book3s/64/hash.h
index d959b0195ad9..222669864ff6 100644
--- a/arch/powerpc/include/asm/book3s/64/hash.h
+++ b/arch/powerpc/include/asm/book3s/64/hash.h
@@ -18,6 +18,10 @@
 #include <asm/book3s/64/hash-4k.h>
 #endif
 
+#define H_PTRS_PER_PTE		(1 << H_PTE_INDEX_SIZE)
+#define H_PTRS_PER_PMD		(1 << H_PMD_INDEX_SIZE)
+#define H_PTRS_PER_PUD		(1 << H_PUD_INDEX_SIZE)
+
 /* Bits to set in a PMD/PUD/PGD entry valid bit*/
 #define HASH_PMD_VAL_BITS		(0x8000000000000000UL)
 #define HASH_PUD_VAL_BITS		(0x8000000000000000UL)
diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index a666d561b44d..49f2a2bbc0cf 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -232,6 +232,10 @@ extern unsigned long __pmd_frag_size_shift;
 #define PTRS_PER_PUD	(1 << PUD_INDEX_SIZE)
 #define PTRS_PER_PGD	(1 << PGD_INDEX_SIZE)
 
+#define MAX_PTRS_PER_PTE ((H_PTRS_PER_PTE > R_PTRS_PER_PTE) ? H_PTRS_PER_PTE : R_PTRS_PER_PTE)
+#define MAX_PTRS_PER_PMD ((H_PTRS_PER_PMD > R_PTRS_PER_PMD) ? H_PTRS_PER_PMD : R_PTRS_PER_PMD)
+#define MAX_PTRS_PER_PUD ((H_PTRS_PER_PUD > R_PTRS_PER_PUD) ? H_PTRS_PER_PUD : R_PTRS_PER_PUD)
+
 /* PMD_SHIFT determines what a second-level page table entry can map */
 #define PMD_SHIFT	(PAGE_SHIFT + PTE_INDEX_SIZE)
 #define PMD_SIZE	(1UL << PMD_SHIFT)
diff --git a/arch/powerpc/include/asm/book3s/64/radix.h b/arch/powerpc/include/asm/book3s/64/radix.h
index 59cab558e2f0..191399143dc8 100644
--- a/arch/powerpc/include/asm/book3s/64/radix.h
+++ b/arch/powerpc/include/asm/book3s/64/radix.h
@@ -35,6 +35,11 @@
 #define RADIX_PMD_SHIFT		(PAGE_SHIFT + RADIX_PTE_INDEX_SIZE)
 #define RADIX_PUD_SHIFT		(RADIX_PMD_SHIFT + RADIX_PMD_INDEX_SIZE)
 #define RADIX_PGD_SHIFT		(RADIX_PUD_SHIFT + RADIX_PUD_INDEX_SIZE)
+
+#define R_PTRS_PER_PTE		(1 << RADIX_PTE_INDEX_SIZE)
+#define R_PTRS_PER_PMD		(1 << RADIX_PMD_INDEX_SIZE)
+#define R_PTRS_PER_PUD		(1 << RADIX_PUD_INDEX_SIZE)
+
 /*
  * Size of EA range mapped by our pagetables.
  */
@@ -68,11 +73,11 @@
  *
  *
  * 3rd quadrant expanded:
- * +------------------------------+
+ * +------------------------------+  Highest address (0xc010000000000000)
+ * +------------------------------+  KASAN shadow end (0xc00fc00000000000)
  * |                              |
  * |                              |
- * |                              |
- * +------------------------------+  Kernel vmemmap end (0xc010000000000000)
+ * +------------------------------+  Kernel vmemmap end/shadow start (0xc00e000000000000)
  * |                              |
  * |           512TB		  |
  * |                              |
@@ -126,6 +131,8 @@
 #define RADIX_VMEMMAP_SIZE	RADIX_KERN_MAP_SIZE
 #define RADIX_VMEMMAP_END	(RADIX_VMEMMAP_START + RADIX_VMEMMAP_SIZE)
 
+/* For the sizes of the shadow area, see kasan.h */
+
 #ifndef __ASSEMBLY__
 #define RADIX_PTE_TABLE_SIZE	(sizeof(pte_t) << RADIX_PTE_INDEX_SIZE)
 #define RADIX_PMD_TABLE_SIZE	(sizeof(pmd_t) << RADIX_PMD_INDEX_SIZE)
diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
index 3c478e5ef24c..6efc822e70fd 100644
--- a/arch/powerpc/include/asm/kasan.h
+++ b/arch/powerpc/include/asm/kasan.h
@@ -30,9 +30,31 @@
 
 #define KASAN_SHADOW_OFFSET	ASM_CONST(CONFIG_KASAN_SHADOW_OFFSET)
 
+#ifdef CONFIG_PPC32
 #define KASAN_SHADOW_END	(-(-KASAN_SHADOW_START >> KASAN_SHADOW_SCALE_SHIFT))
+#endif
 
 #ifdef CONFIG_KASAN
+#ifdef CONFIG_PPC_BOOK3S_64
+/*
+ * The shadow ends before the highest accessible address
+ * because we don't need a shadow for the shadow. Instead:
+ * c00e000000000000 << 3 + a80e000000000000 = c00fc00000000000
+ */
+#define KASAN_SHADOW_END 0xc00fc00000000000UL
+
+DECLARE_STATIC_KEY_FALSE(powerpc_kasan_enabled_key);
+
+static __always_inline bool kasan_arch_is_ready(void)
+{
+	if (static_branch_likely(&powerpc_kasan_enabled_key))
+		return true;
+	return false;
+}
+
+#define kasan_arch_is_ready kasan_arch_is_ready
+#endif
+
 void kasan_early_init(void);
 void kasan_mmu_init(void);
 void kasan_init(void);
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index f66b63e81c3b..aabac84106f1 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -32,6 +32,17 @@ KASAN_SANITIZE_early_32.o := n
 KASAN_SANITIZE_cputable.o := n
 KASAN_SANITIZE_prom_init.o := n
 KASAN_SANITIZE_btext.o := n
+KASAN_SANITIZE_paca.o := n
+KASAN_SANITIZE_setup_64.o := n
+KASAN_SANITIZE_mce.o := n
+KASAN_SANITIZE_mce_power.o := n
+
+# we have to be particularly careful in ppc64 to exclude code that
+# runs with translations off, as we cannot access the shadow with
+# translations off. However, ppc32 can sanitize this.
+ifdef CONFIG_PPC64
+KASAN_SANITIZE_traps.o := n
+endif
 
 ifdef CONFIG_KASAN
 CFLAGS_early_32.o += -DDISABLE_BRANCH_PROFILING
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 89e34aa273e2..430cf06f9406 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -2151,8 +2151,8 @@ void show_stack(struct task_struct *tsk, unsigned long *stack,
 			break;
 
 		stack = (unsigned long *) sp;
-		newsp = stack[0];
-		ip = stack[STACK_FRAME_LR_SAVE];
+		newsp = READ_ONCE_NOCHECK(stack[0]);
+		ip = READ_ONCE_NOCHECK(stack[STACK_FRAME_LR_SAVE]);
 		if (!firstframe || ip != lr) {
 			printk("%s["REG"] ["REG"] %pS",
 				loglvl, sp, ip, (void *)ip);
@@ -2170,17 +2170,19 @@ void show_stack(struct task_struct *tsk, unsigned long *stack,
 		 * See if this is an exception frame.
 		 * We look for the "regshere" marker in the current frame.
 		 */
-		if (validate_sp(sp, tsk, STACK_FRAME_WITH_PT_REGS)
-		    && stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
+		if (validate_sp(sp, tsk, STACK_FRAME_WITH_PT_REGS) &&
+		    (READ_ONCE_NOCHECK(stack[STACK_FRAME_MARKER]) ==
+		     STACK_FRAME_REGS_MARKER)) {
 			struct pt_regs *regs = (struct pt_regs *)
 				(sp + STACK_FRAME_OVERHEAD);
 
-			lr = regs->link;
+			lr = READ_ONCE_NOCHECK(regs->link);
 			printk("%s--- interrupt: %lx at %pS\n",
-			       loglvl, regs->trap, (void *)regs->nip);
+			       loglvl, READ_ONCE_NOCHECK(regs->trap),
+			       (void *)READ_ONCE_NOCHECK(regs->nip));
 			__show_regs(regs);
 			printk("%s--- interrupt: %lx\n",
-			       loglvl, regs->trap);
+			       loglvl, READ_ONCE_NOCHECK(regs->trap));
 
 			firstframe = 1;
 		}
diff --git a/arch/powerpc/kvm/Makefile b/arch/powerpc/kvm/Makefile
index 2bfeaa13befb..7f1592dacbeb 100644
--- a/arch/powerpc/kvm/Makefile
+++ b/arch/powerpc/kvm/Makefile
@@ -136,3 +136,8 @@ obj-$(CONFIG_KVM_BOOK3S_64_PR) += kvm-pr.o
 obj-$(CONFIG_KVM_BOOK3S_64_HV) += kvm-hv.o
 
 obj-y += $(kvm-book3s_64-builtin-objs-y)
+
+# KVM does a lot in real-mode, and 64-bit Book3S KASAN doesn't support that
+ifdef CONFIG_PPC_BOOK3S_64
+KASAN_SANITIZE := n
+endif
diff --git a/arch/powerpc/mm/book3s64/Makefile b/arch/powerpc/mm/book3s64/Makefile
index 1b56d3af47d4..a7d8a68bd2c5 100644
--- a/arch/powerpc/mm/book3s64/Makefile
+++ b/arch/powerpc/mm/book3s64/Makefile
@@ -21,3 +21,12 @@ obj-$(CONFIG_PPC_PKEY)	+= pkeys.o
 
 # Instrumenting the SLB fault path can lead to duplicate SLB entries
 KCOV_INSTRUMENT_slb.o := n
+
+# Parts of these can run in real mode and therefore are
+# not safe with the current outline KASAN implementation
+KASAN_SANITIZE_mmu_context.o := n
+KASAN_SANITIZE_pgtable.o := n
+KASAN_SANITIZE_radix_pgtable.o := n
+KASAN_SANITIZE_radix_tlb.o := n
+KASAN_SANITIZE_slb.o := n
+KASAN_SANITIZE_pkeys.o := n
diff --git a/arch/powerpc/mm/kasan/Makefile b/arch/powerpc/mm/kasan/Makefile
index 42fb628a44fd..07eef87abd6c 100644
--- a/arch/powerpc/mm/kasan/Makefile
+++ b/arch/powerpc/mm/kasan/Makefile
@@ -5,3 +5,4 @@ KASAN_SANITIZE := n
 obj-$(CONFIG_PPC32)           += init_32.o
 obj-$(CONFIG_PPC_8xx)		+= 8xx.o
 obj-$(CONFIG_PPC_BOOK3S_32)	+= book3s_32.o
+obj-$(CONFIG_PPC_BOOK3S_64)   += init_book3s_64.o
diff --git a/arch/powerpc/mm/kasan/init_book3s_64.c b/arch/powerpc/mm/kasan/init_book3s_64.c
new file mode 100644
index 000000000000..ca913ed951a2
--- /dev/null
+++ b/arch/powerpc/mm/kasan/init_book3s_64.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KASAN for 64-bit Book3S powerpc
+ *
+ * Copyright (C) 2019-2020 IBM Corporation
+ * Author: Daniel Axtens <dja@axtens.net>
+ */
+
+#define DISABLE_BRANCH_PROFILING
+
+#include <linux/kasan.h>
+#include <linux/printk.h>
+#include <linux/sched/task.h>
+#include <linux/memblock.h>
+#include <asm/pgalloc.h>
+
+DEFINE_STATIC_KEY_FALSE(powerpc_kasan_enabled_key);
+
+static void __init kasan_init_phys_region(void *start, void *end)
+{
+	unsigned long k_start, k_end, k_cur;
+	void *va;
+
+	if (start >= end)
+		return;
+
+	k_start = ALIGN_DOWN((unsigned long)kasan_mem_to_shadow(start), PAGE_SIZE);
+	k_end = ALIGN((unsigned long)kasan_mem_to_shadow(end), PAGE_SIZE);
+
+	va = memblock_alloc(k_end - k_start, PAGE_SIZE);
+	for (k_cur = k_start; k_cur < k_end; k_cur += PAGE_SIZE, va += PAGE_SIZE)
+		map_kernel_page(k_cur, __pa(va), PAGE_KERNEL);
+}
+
+void __init kasan_init(void)
+{
+	/*
+	 * We want to do the following things:
+	 *  1) Map real memory into the shadow for all physical memblocks
+	 *     This takes us from c000... to c008...
+	 *  2) Leave a hole over the shadow of vmalloc space. KASAN_VMALLOC
+	 *     will manage this for us.
+	 *     This takes us from c008... to c00a...
+	 *  3) Map the 'early shadow'/zero page over iomap and vmemmap space.
+	 *     This takes us up to where we start at c00e...
+	 */
+
+	void *k_start = kasan_mem_to_shadow((void *)RADIX_VMALLOC_END);
+	void *k_end = kasan_mem_to_shadow((void *)RADIX_VMEMMAP_END);
+	phys_addr_t start, end;
+	u64 i;
+	pte_t zero_pte = pfn_pte(virt_to_pfn(kasan_early_shadow_page), PAGE_KERNEL);
+
+	if (!early_radix_enabled())
+		panic("KASAN requires radix!");
+
+	for_each_mem_range(i, &start, &end)
+		kasan_init_phys_region((void *)start, (void *)end);
+
+	for (i = 0; i < PTRS_PER_PTE; i++)
+		__set_pte_at(&init_mm, (unsigned long)kasan_early_shadow_page,
+			     &kasan_early_shadow_pte[i], zero_pte, 0);
+
+	for (i = 0; i < PTRS_PER_PMD; i++)
+		pmd_populate_kernel(&init_mm, &kasan_early_shadow_pmd[i],
+				    kasan_early_shadow_pte);
+
+	for (i = 0; i < PTRS_PER_PUD; i++)
+		pud_populate(&init_mm, &kasan_early_shadow_pud[i],
+			     kasan_early_shadow_pmd);
+
+	/* map the early shadow over the iomap and vmemmap space */
+	kasan_populate_early_shadow(k_start, k_end);
+
+	/* mark early shadow region as RO and wipe it */
+	zero_pte = pfn_pte(virt_to_pfn(kasan_early_shadow_page), PAGE_KERNEL_RO);
+	for (i = 0; i < PTRS_PER_PTE; i++)
+		__set_pte_at(&init_mm, (unsigned long)kasan_early_shadow_page,
+			     &kasan_early_shadow_pte[i], zero_pte, 0);
+
+	/*
+	 * clear_page relies on some cache info that hasn't been set up yet.
+	 * It ends up looping ~forever and blows up other data.
+	 * Use memset instead.
+	 */
+	memset(kasan_early_shadow_page, 0, PAGE_SIZE);
+
+	static_branch_inc(&powerpc_kasan_enabled_key);
+
+	/* Enable error messages */
+	init_task.kasan_depth = 0;
+	pr_info("KASAN init done (64-bit Book3S)\n");
+}
+
+void __init kasan_late_init(void) { }
diff --git a/arch/powerpc/mm/ptdump/ptdump.c b/arch/powerpc/mm/ptdump/ptdump.c
index aca354fb670b..63672aa656e8 100644
--- a/arch/powerpc/mm/ptdump/ptdump.c
+++ b/arch/powerpc/mm/ptdump/ptdump.c
@@ -20,6 +20,7 @@
 #include <linux/seq_file.h>
 #include <asm/fixmap.h>
 #include <linux/const.h>
+#include <linux/kasan.h>
 #include <asm/page.h>
 #include <asm/hugetlb.h>
 
@@ -317,6 +318,23 @@ static void walk_pud(struct pg_state *st, p4d_t *p4d, unsigned long start)
 	unsigned long addr;
 	unsigned int i;
 
+#if defined(CONFIG_KASAN) && defined(CONFIG_PPC_BOOK3S_64)
+	/*
+	 * On radix + KASAN, we want to check for the KASAN "early" shadow
+	 * which covers huge quantities of memory with the same set of
+	 * read-only PTEs. If it is, we want to note the first page (to see
+	 * the status change), and then note the last page. This gives us good
+	 * results without spending ages noting the exact same PTEs over 100s of
+	 * terabytes of memory.
+	 */
+	if (p4d_page(*p4d) == virt_to_page(lm_alias(kasan_early_shadow_pud))) {
+		walk_pmd(st, pud, start);
+		addr = start + (PTRS_PER_PUD - 1) * PUD_SIZE;
+		walk_pmd(st, pud, addr);
+		return;
+	}
+#endif
+
 	for (i = 0; i < PTRS_PER_PUD; i++, pud++) {
 		addr = start + i * PUD_SIZE;
 		if (!pud_none(*pud) && !pud_is_leaf(*pud))
@@ -387,11 +405,11 @@ static void populate_markers(void)
 #endif
 	address_markers[i++].start_address = FIXADDR_START;
 	address_markers[i++].start_address = FIXADDR_TOP;
+#endif /* CONFIG_PPC64 */
 #ifdef CONFIG_KASAN
 	address_markers[i++].start_address = KASAN_SHADOW_START;
 	address_markers[i++].start_address = KASAN_SHADOW_END;
 #endif
-#endif /* CONFIG_PPC64 */
 }
 
 static int ptdump_show(struct seq_file *m, void *v)
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 113431604035..de70bfea2982 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -105,6 +105,7 @@ config PPC_BOOK3S_64
 	select PPC_MM_SLICES
 	select PPC_HAVE_KUEP
 	select PPC_HAVE_KUAP
+	select KASAN_VMALLOC if KASAN
 
 config PPC_BOOK3E_64
 	bool "Embedded processors"
diff --git a/arch/powerpc/platforms/powernv/Makefile b/arch/powerpc/platforms/powernv/Makefile
index be2546b96816..d50f6fc71ac6 100644
--- a/arch/powerpc/platforms/powernv/Makefile
+++ b/arch/powerpc/platforms/powernv/Makefile
@@ -1,4 +1,10 @@
 # SPDX-License-Identifier: GPL-2.0
+
+# nothing that deals with real mode is safe to KASAN
+# in particular, idle code runs a bunch of things in real mode
+KASAN_SANITIZE_idle.o := n
+KASAN_SANITIZE_pci-ioda.o := n
+
 obj-y			+= setup.o opal-call.o opal-wrappers.o opal.o opal-async.o
 obj-y			+= idle.o opal-rtc.o opal-nvram.o opal-lpc.o opal-flash.o
 obj-y			+= rng.o opal-elog.o opal-dump.o opal-sysparam.o opal-sensor.o
diff --git a/arch/powerpc/platforms/pseries/Makefile b/arch/powerpc/platforms/pseries/Makefile
index c8a2b0b05ac0..202199ef9e5c 100644
--- a/arch/powerpc/platforms/pseries/Makefile
+++ b/arch/powerpc/platforms/pseries/Makefile
@@ -30,3 +30,6 @@ obj-$(CONFIG_PPC_SVM)		+= svm.o
 obj-$(CONFIG_FA_DUMP)		+= rtas-fadump.o
 
 obj-$(CONFIG_SUSPEND)		+= suspend.o
+
+# nothing that operates in real mode is safe for KASAN
+KASAN_SANITIZE_ras.o := n
-- 
2.27.0

Re: [PATCH v12 1/6] kasan: allow an architecture to disable inline instrumentation

[Marco Elver]

On Tue, 15 Jun 2021 at 03:47, 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.
>
> Signed-off-by: Daniel Axtens <dja@axtens.net>
> ---
>  lib/Kconfig.kasan | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index cffc2ebbf185..935814f332a7 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -12,6 +12,15 @@ config HAVE_ARCH_KASAN_HW_TAGS
>  config HAVE_ARCH_KASAN_VMALLOC
>         bool
>
> +# Sometimes an architecture might not be able to support inline instrumentation
> +# but might be able to support outline instrumentation. This option allows an
> +# arch to prevent inline and stack instrumentation from being enabled.

This comment could be moved into 'help' of this new config option.

> +# ppc64 turns on virtual memory late in boot, after calling into generic code
> +# like the device-tree parser, so it uses this in conjuntion with a hook in
> +# outline mode to avoid invalid access early in boot.

I think the ppc64-related comment isn't necessary and can be moved to
arch/ppc64 somewhere, if there isn't one already.

> +config ARCH_DISABLE_KASAN_INLINE
> +       bool
> +
>  config CC_HAS_KASAN_GENERIC
>         def_bool $(cc-option, -fsanitize=kernel-address)
>
> @@ -130,6 +139,7 @@ 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 +151,7 @@ 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 +165,9 @@ 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, this is
> +         also disabled as it adds inline-style instrumentation that
> +         is run unconditionally.
>
>  config KASAN_SW_TAGS_IDENTIFY
>         bool "Enable memory corruption identification"
> --
> 2.27.0
>
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Re: [PATCH v12 2/6] kasan: allow architectures to provide an outline readiness check

[Marco Elver]

On Tue, 15 Jun 2021 at 03:47, 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.vnet.ibm.com>
> Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> Signed-off-by: Daniel Axtens <dja@axtens.net>
>
> --
>
> I discuss the justfication for this later in the series. Also,
> 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
> ---
>  mm/kasan/common.c  | 4 ++++
>  mm/kasan/generic.c | 3 +++
>  mm/kasan/kasan.h   | 4 ++++
>  mm/kasan/shadow.c  | 4 ++++
>  4 files changed, 15 insertions(+)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 10177cc26d06..0ad615f3801d 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -331,6 +331,10 @@ static inline bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
>         u8 tag;
>         void *tagged_object;
>
> +       /* Bail if the arch isn't ready */
> +       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..19323a3d5975 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -449,6 +449,10 @@ 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; }
> +#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..74134b657d7d 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -73,6 +73,10 @@ void kasan_poison(const void *addr, size_t size, u8 value, bool init)
>  {
>         void *shadow_start, *shadow_end;
>
> +       /* Don't touch the shadow memory if arch isn't ready */
> +       if (!kasan_arch_is_ready())
> +               return;
> +

What about kasan_poison_last_granule()? kasan_unpoison() currently
seems to potentially trip on that.

Re: [PATCH v12 0/6] KASAN core changes for ppc64 radix KASAN

[Marco Elver]

[+Cc Andrey]

On Tue, 15 Jun 2021 at 03:47, Daniel Axtens <dja@axtens.net> wrote:
>
> 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. So my aim here is for patches 1 through 4 or 1 through 5
> to go in via the mm tree.

I think this is reasonable. I'd suggest just sending non-ppc patches
separately (i.e. split the series explicitly) to KASAN maintainers,
and ensure to Cc Andrew, too. Just point at this series to illustrate
how it'll be used.

I think the patches are fine, but I'm not entirely sure about the
current placements of kasan_arch_is_ready(), so hopefully Andrey can
also have a look.


> I will then propose the powerpc changes for
> a later cycle. (I have attached them to this series as an RFC, and
> there are still outstanding review comments I need to attend to.)
>
> v12 applies to next-20210611. There should be no noticable changes to
> other platforms.
>
> Kind regards,
> Daniel
>
> Daniel Axtens (6):
>   kasan: allow an architecture to disable inline instrumentation
>   kasan: allow architectures to provide an outline readiness check
>   kasan: define and use MAX_PTRS_PER_* for early shadow tables

^^ Up to here could be a separate series to go through -mm.

>   kasan: Document support on 32-bit powerpc

^^ The Documentation changes are minimal and not just confined to
kasan.rst it seems. In fact your "powerpc: Book3S .." patch changes
Documentation more. So you could just take "kasan: Document support on
32-bit powerpc" through ppc tree as well.

>   powerpc/mm/kasan: rename kasan_init_32.c to init_32.c
>   [RFC] powerpc: Book3S 64-bit outline-only KASAN support

Re: [PATCH v12 1/6] kasan: allow an architecture to disable inline instrumentation

[Daniel Axtens]

Hi Marco,

@@ -12,6 +12,15 @@ config HAVE_ARCH_KASAN_HW_TAGS
>>  config HAVE_ARCH_KASAN_VMALLOC
>>         bool
>>
>> +# Sometimes an architecture might not be able to support inline instrumentation
>> +# but might be able to support outline instrumentation. This option allows an
>> +# arch to prevent inline and stack instrumentation from being enabled.
>
> This comment could be moved into 'help' of this new config option.

It could. I did wonder if that made sense given that this is not a user
selectable option so I'm not sure if the help will ever be visible, but
I see that we do this sort of thing in Kconfig.kcsan and Kconfig.kgdb.
I've changed it over.

>> +# ppc64 turns on virtual memory late in boot, after calling into generic code
>> +# like the device-tree parser, so it uses this in conjuntion with a hook in
>> +# outline mode to avoid invalid access early in boot.
>
> I think the ppc64-related comment isn't necessary and can be moved to
> arch/ppc64 somewhere, if there isn't one already.

Fair enough. I'll pull it out of this file and look for a good place to
put the information in arch/powerpc in a later patch/series.

Kind regards,
Daniel

Re: [PATCH v12 2/6] kasan: allow architectures to provide an outline readiness check

[Daniel Axtens]

Hi Marco,
>> +       /* Don't touch the shadow memory if arch isn't ready */
>> +       if (!kasan_arch_is_ready())
>> +               return;
>> +
>
> What about kasan_poison_last_granule()? kasan_unpoison() currently
> seems to potentially trip on that.

Ah the perils of rebasing an old series! I'll re-audit the generic code
for functions that touch memory and make sure I have covered them all.

Thanks for the review.

Kind regards,
Daniel

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