[PATCH v10 0/6] KASAN for powerpc64 radix

[PATCH v10 0/6] KASAN for powerpc64 radix

[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.

v10 rebases on top of next-20210125, fixing things up to work on top
of the latest changes, and fixing some review comments from
Christophe. I have tested host and guest with 64k pages for this spin.

It does not apply to powerpc/next, sorry: there are conflicting kasan
changes staged in next.

There is now only 1 failing KUnit test: kasan_global_oob - gcc puts
the ASAN init code in a section called '.init_array'. Powerpc64 module
loading code goes through and _renames_ any section beginning with
'.init' to begin with '_init' in order to avoid some complexities
around our 24-bit indirect jumps. This means it renames '.init_array'
to '_init_array', and the generic module loading code then fails to
recognise the section as a constructor and thus doesn't run it. This
hack dates back to 2003 and so I'm not going to try to unpick it in
this series. (I suspect this may have previously worked if the code
ended up in .ctors rather than .init_array but I don't keep my old
binaries around so I have no real way of checking.)

(The previously failing stack tests are now skipped due to more
accurate configuration settings.)

Details from v9: This is a significant reworking of the previous
versions. Instead of the previous approach which supported inline
instrumentation, this series provides only outline instrumentation.

To get around the problem of accessing the shadow region inside code we run
with translations off (in 'real mode'), we we restrict checking to when
translations are enabled. This is done via a new hook in the kasan core and
by excluding larger quantites of arch code from instrumentation. The upside
is that we no longer require that you be able to specify the amount of
physically contiguous memory on the system at compile time. Hopefully this
is a better trade-off. More details in patch 6.

kexec works. Both 64k and 4k pages work. Running as a KVM host works, but
nothing in arch/powerpc/kvm is instrumented. It's also potentially a bit
fragile - if any real mode code paths call out to instrumented code, things
will go boom.

Kind regards,
Daniel

[PATCH v10 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 | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index cffc2ebbf185..4f4d3fb8733d 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -12,6 +12,9 @@ config HAVE_ARCH_KASAN_HW_TAGS
 config HAVE_ARCH_KASAN_VMALLOC
 	bool
 
+config ARCH_DISABLE_KASAN_INLINE
+	def_bool n
+
 config CC_HAS_KASAN_GENERIC
 	def_bool $(cc-option, -fsanitize=kernel-address)
 
@@ -130,6 +133,7 @@ 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 +145,7 @@ 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 +159,9 @@ 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 v10 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
---
 include/linux/kasan.h | 4 ++++
 mm/kasan/common.c     | 4 ++++
 mm/kasan/generic.c    | 3 +++
 mm/kasan/shadow.c     | 4 ++++
 4 files changed, 15 insertions(+)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index bb862d1f0e15..d314c0fa5804 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -23,6 +23,10 @@ struct kunit_kasan_expectation {
 
 #endif
 
+#ifndef kasan_arch_is_ready
+static inline bool kasan_arch_is_ready(void)	{ return true; }
+#endif
+
 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
 
 #include <linux/pgtable.h>
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index a390fae9d64b..871ceefd723d 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -348,6 +348,10 @@ static bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
 	if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
 		return false;
 
+	/* We can't read the shadow byte if the arch isn't ready */
+	if (!kasan_arch_is_ready())
+		return false;
+
 	if (!kasan_byte_accessible(tagged_object)) {
 		kasan_report_invalid_free(tagged_object, ip);
 		return true;
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 2e55e0f82f39..718c171584e3 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/shadow.c b/mm/kasan/shadow.c
index de6b3f074742..0aafc2d5138f 100644
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -85,6 +85,10 @@ void kasan_poison(const void *address, size_t size, u8 value)
 	address = kasan_reset_tag(address);
 	size = round_up(size, KASAN_GRANULE_SIZE);
 
+	/* Don't touch the shadow memory if arch isn't ready */
+	if (!kasan_arch_is_ready())
+		return;
+
 	/* Skip KFENCE memory if called explicitly outside of sl*b. */
 	if (is_kfence_address(address))
 		return;
-- 
2.27.0

[PATCH v10 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 d314c0fa5804..84bea59d01b3 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -43,10 +43,22 @@ static inline bool kasan_arch_is_ready(void)	{ return true; }
 #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 c4605ac9837b..b4d822dff1fb 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 v10 4/6] kasan: Document support on 32-bit powerpc

[Daniel Axtens]

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

Document s390 support while we're at it.

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 |  7 +++++--
 Documentation/powerpc/kasan.txt   | 12 ++++++++++++
 2 files changed, 17 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 e022b7506e37..9cfc116cc6bf 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -22,7 +22,8 @@ out-of-bounds accesses for global variables is only supported since Clang 11.
 Tag-based KASAN is only supported in Clang.
 
 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
 -----
@@ -332,7 +333,9 @@ CONFIG_KASAN_VMALLOC
 ~~~~~~~~~~~~~~~~~~~~
 
 With ``CONFIG_KASAN_VMALLOC``, KASAN can cover vmalloc space at the
-cost of greater memory usage. Currently this is only supported on x86.
+cost of greater memory usage. Currently this supported on x86, 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 v10 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 v10 6/6] powerpc: Book3S 64-bit outline-only KASAN support

[Daniel Axtens]

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.

 - Make our stack-walking code KASAN-safe by using READ_ONCE_NOCHECK -
   generic code, arm64, s390 and x86 all do this for similar sorts of
   reasons: when unwinding a stack, we might touch memory that KASAN has
   marked as being out-of-bounds. In our case we often get this when
   checking for an exception frame because we're checking an arbitrary
   offset into the stack frame.

   See commit 20955746320e ("s390/kasan: avoid false positives during stack
   unwind"), commit bcaf669b4bdb ("arm64: disable kasan when accessing
   frame->fp in unwind_frame"), commit 91e08ab0c851 ("x86/dumpstack:
   Prevent KASAN false positive warnings") and commit 6e22c8366416
   ("tracing, kasan: Silence Kasan warning in check_stack of stack_tracer")

 - 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: Balbir Singh <bsingharora@gmail.com> # ppc64 out-of-line radix version
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> # ppc64 hash version
Cc: Christophe Leroy <christophe.leroy@csgroup.eu> # ppc32 version
Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 Documentation/dev-tools/kasan.rst            |  9 +-
 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, 256 insertions(+), 18 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 9cfc116cc6bf..8c5d0c5c35f6 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -22,8 +22,9 @@ out-of-bounds accesses for global variables is only supported since Clang 11.
 Tag-based KASAN is only supported in Clang.
 
 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 powerpc
+kernels and for 64-bit kernels running under the Radix MMU. Tag-based KASAN
+modes are supported only for arm64.
 
 Usage
 -----
@@ -334,8 +335,8 @@ CONFIG_KASAN_VMALLOC
 
 With ``CONFIG_KASAN_VMALLOC``, KASAN can cover vmalloc space at the
 cost of greater memory usage. Currently this supported on x86, s390
-and 32-bit powerpc. It is optional, except on 32-bit powerpc kernels
-with module support, where it is required.
+and powerpc. 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 9141f03060ce..a1f359ec2fa1 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_HAS_DEBUG_VIRTUAL
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ELF_RANDOMIZE
@@ -183,7 +184,8 @@ config PPC
 	select HAVE_ARCH_HUGE_VMAP		if PPC_BOOK3S_64 && PPC_RADIX_MMU
 	select HAVE_ARCH_JUMP_LABEL
 	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_KGDB
 	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if COMPAT
diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index b88900f4832f..33e4cc8c4306 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -397,4 +397,5 @@ 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 a39886681629..891084efdad7 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -230,6 +230,10 @@ 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 c7813dc628fc..b3492b80f858 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 7355ed05e65e..fdcce89c2515 100644
--- a/arch/powerpc/include/asm/kasan.h
+++ b/arch/powerpc/include/asm/kasan.h
@@ -30,7 +30,29 @@
 
 #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_PPC_BOOK3S_64
+/*
+ * The shadow ends before the highest accessible address
+ * because we don't need a shadow for the shadow. Instead:
+ * c00e000000000000 << 3 + a80e000000000000000 = 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
 
 #ifdef CONFIG_KASAN
 void kasan_early_init(void);
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index fe2ef598e2ea..a0cbe8953238 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 a66f435dabbf..9a6fd603f0e7 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -2157,8 +2157,8 @@ 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);
@@ -2176,17 +2176,19 @@ 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_INT_FRAME_SIZE)
-		    && stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
+		if (validate_sp(sp, tsk, STACK_INT_FRAME_SIZE) &&
+		    (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 3ce907523b1e..9063c13e7221 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -101,6 +101,7 @@ config PPC_BOOK3S_64
 	select ARCH_SUPPORTS_NUMA_BALANCING
 	select IRQ_WORK
 	select PPC_MM_SLICES
+	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 2eb6ae150d1f..f277e4793696 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 v10 6/6] powerpc: Book3S 64-bit outline-only KASAN support

[Christophe Leroy]

Le 03/02/2021 à 12:59, Daniel Axtens a écrit :
> Implement a limited form of KASAN for Book3S 64-bit machines running under
> the Radix MMU, supporting only outline mode.
> 

> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index a66f435dabbf..9a6fd603f0e7 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -2157,8 +2157,8 @@ 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);
> @@ -2176,17 +2176,19 @@ 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_INT_FRAME_SIZE)
> -		    && stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
> +		if (validate_sp(sp, tsk, STACK_INT_FRAME_SIZE) &&
> +		    (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;
>   		}


The above changes look like a bug fix not directly related to KASAN. Should be split out in another 
patch I think.

Christophe

Re: [PATCH v10 6/6] powerpc: Book3S 64-bit outline-only KASAN support

[Daniel Axtens]

Christophe Leroy <christophe.leroy@csgroup.eu> writes:

> Le 03/02/2021 à 12:59, Daniel Axtens a écrit :
>> Implement a limited form of KASAN for Book3S 64-bit machines running under
>> the Radix MMU, supporting only outline mode.
>> 
>
>> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
>> index a66f435dabbf..9a6fd603f0e7 100644
>> --- a/arch/powerpc/kernel/process.c
>> +++ b/arch/powerpc/kernel/process.c
>> @@ -2157,8 +2157,8 @@ 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);
>> @@ -2176,17 +2176,19 @@ 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_INT_FRAME_SIZE)
>> -		    && stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
>> +		if (validate_sp(sp, tsk, STACK_INT_FRAME_SIZE) &&
>> +		    (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;
>>   		}
>
>
> The above changes look like a bug fix not directly related to KASAN. Should be split out in another 
> patch I think.

That code corresponds to the following part of the patch description:

| - Make our stack-walking code KASAN-safe by using READ_ONCE_NOCHECK -
|   generic code, arm64, s390 and x86 all do this for similar sorts of
|   reasons: when unwinding a stack, we might touch memory that KASAN has
|   marked as being out-of-bounds. In our case we often get this when
|   checking for an exception frame because we're checking an arbitrary
|   offset into the stack frame.
|
|   See commit 20955746320e ("s390/kasan: avoid false positives during stack
|   unwind"), commit bcaf669b4bdb ("arm64: disable kasan when accessing
|   frame->fp in unwind_frame"), commit 91e08ab0c851 ("x86/dumpstack:
|   Prevent KASAN false positive warnings") and commit 6e22c8366416
|   ("tracing, kasan: Silence Kasan warning in check_stack of stack_tracer")

include/linux/compiler.h describes it as follows:

/*
 * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
 * to hide memory access from KASAN.
 */

So I think it is sufficently connected with KASAN to be in this patch.

Kind regards,
Daniel

>
> Christophe