Message-ID: <251530bd-49ab-4d6e-13bc-03f97edafcc4@csgroup.eu>
Date:   Tue, 1 Dec 2020 18:26:04 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Daniel Axtens <dja@...ens.net>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        kasan-dev@...glegroups.com, christophe.leroy@....fr,
        aneesh.kumar@...ux.ibm.com, bsingharora@...il.com
Subject: Re: [PATCH v9 6/6] powerpc: Book3S 64-bit outline-only KASAN support



Le 01/12/2020 à 17:16, Daniel Axtens a écrit :
> 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@...il.com> # ppc64 out-of-line radix version
> Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com> # ppc64 hash version
> Cc: Christophe Leroy <christophe.leroy@....fr> # ppc32 version
> Signed-off-by: Daniel Axtens <dja@...ens.net>
> ---
>   Documentation/dev-tools/kasan.rst            |  9 +-
>   Documentation/powerpc/kasan.txt              | 48 +++++++++-
>   arch/powerpc/Kconfig                         |  4 +-
>   arch/powerpc/Kconfig.debug                   |  2 +-
>   arch/powerpc/include/asm/book3s/64/hash.h    |  4 +
>   arch/powerpc/include/asm/book3s/64/pgtable.h |  7 ++
>   arch/powerpc/include/asm/book3s/64/radix.h   | 13 ++-
>   arch/powerpc/include/asm/kasan.h             | 34 ++++++-
>   arch/powerpc/kernel/Makefile                 |  5 +
>   arch/powerpc/kernel/process.c                | 16 ++--
>   arch/powerpc/kvm/Makefile                    |  5 +
>   arch/powerpc/mm/book3s64/Makefile            |  8 ++
>   arch/powerpc/mm/kasan/Makefile               |  1 +
>   arch/powerpc/mm/kasan/init_book3s_64.c       | 98 ++++++++++++++++++++
>   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, 265 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 eaf868094a8e..28f08959bd2e 100644
> --- a/Documentation/dev-tools/kasan.rst
> +++ b/Documentation/dev-tools/kasan.rst
> @@ -19,8 +19,9 @@ 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, arm64, xtensa, s390 and
> -riscv architectures. It is also supported on 32-bit powerpc kernels. Tag-based
> -KASAN is supported only on arm64.
> +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 is supported
> +only on arm64.
>   
>   Usage
>   -----
> @@ -257,8 +258,8 @@ 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 e9f13fe08492..e6bd02af6ebd 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -180,7 +180,9 @@ 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_BOOK3S_64 && PPC_RADIX_MMU

PPC_RADIX_MMU already depends on PPC_BOOK3S_64 so 'if PPC_RADIX_MMU' would be enough

> +	select HAVE_ARCH_NO_KASAN_INLINE	if PPC_BOOK3S_64 && PPC_RADIX_MMU

This list must respect Alphabetical order.

> +	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..60c1bba72a6f 100644
> --- a/arch/powerpc/Kconfig.debug
> +++ b/arch/powerpc/Kconfig.debug
> @@ -396,5 +396,5 @@ config PPC_FAST_ENDIAN_SWITCH
>   
>   config KASAN_SHADOW_OFFSET
>   	hex
> -	depends on KASAN
> +	depends on KASAN && PPC32
>   	default 0xe0000000

Instead of the above, why not doing:

	default 0xe0000000 if PPC32
	default 0xa80e000000000000 is PPC_BOOK3S_64

> diff --git a/arch/powerpc/include/asm/book3s/64/hash.h b/arch/powerpc/include/asm/book3s/64/hash.h
> index 73ad038ed10b..105b90594a8a 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..767e239d75e3 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -230,6 +230,13 @@ 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)

Nowadays we allow 100 chars per line. Could this fit on a single line ?

> +#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..c72fd9281b44 100644
> --- a/arch/powerpc/include/asm/kasan.h
> +++ b/arch/powerpc/include/asm/kasan.h
> @@ -28,9 +28,41 @@
>   #define KASAN_SHADOW_START	(KASAN_SHADOW_OFFSET + \
>   				 (KASAN_KERN_START >> KASAN_SHADOW_SCALE_SHIFT))
>   
> +#ifdef CONFIG_KASAN_SHADOW_OFFSET
>   #define KASAN_SHADOW_OFFSET	ASM_CONST(CONFIG_KASAN_SHADOW_OFFSET)
> +#endif
>   
> +#ifdef CONFIG_PPC32
>   #define KASAN_SHADOW_END	(-(-KASAN_SHADOW_START >> KASAN_SHADOW_SCALE_SHIFT))
> +#endif
> +
> +#ifdef CONFIG_PPC_BOOK3S_64
> +/*
> + * We define the  offset such that the shadow of the linear map lives
> + * at the end of vmemmap space, that is, we choose offset such that
> + * shadow(c000_0000_0000_0000) = c00e_0000_0000_0000. This gives:
> + * c00e000000000000 - c000000000000000 >> 3 = a80e000000000000
> + */
> +#define KASAN_SHADOW_OFFSET ASM_CONST(0xa80e000000000000)

Why can't you use CONFIG_KASAN_SHADOW_OFFSET ?

> +
> +/*
> + * 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

I think we should be able to have a common formula for PPC32 and PPC64.

> +
> +DECLARE_STATIC_KEY_FALSE(powerpc_kasan_enabled_key);
> +
> +static inline bool kasan_arch_is_ready_ppc64(void)

I'd make it __always_inline

> +{
> +	if (static_branch_likely(&powerpc_kasan_enabled_key))
> +		return true;
> +	return false;
> +}
> +
> +#define kasan_arch_is_ready kasan_arch_is_ready_ppc64

Usually we keep the generic name, you don't need to have an arch specific name.

> +#endif
>   
>   #ifdef CONFIG_KASAN
>   void kasan_early_init(void);
> @@ -47,5 +79,5 @@ void kasan_update_early_region(unsigned long k_start, unsigned long k_end, pte_t
>   int kasan_init_shadow_page_tables(unsigned long k_start, unsigned long k_end);
>   int kasan_init_region(void *start, size_t size);
>   
> -#endif /* __ASSEMBLY */
> +#endif /* !__ASSEMBLY__ */

This patch is already big. Is that worth it ?

>   #endif
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index fe2ef598e2ea..cd58202459dd 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -32,6 +32,11 @@ 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

The entire setup_64 ?
Can you split things out into an early_64.o like was done for ppc32 ?

> +KASAN_SANITIZE_mce.o := n
> +KASAN_SANITIZE_traps.o := n

Why ? ppc32 doesn't need that.

> +KASAN_SANITIZE_mce_power.o := n
>   
>   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 d421a2c7f822..f02b2766015c 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);
> @@ -2170,14 +2170,16 @@ 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    LR = %pS\n",
> -			       loglvl, regs->trap,
> -			       (void *)regs->nip, (void *)lr);
> +			       loglvl, READ_ONCE_NOCHECK(regs->trap),
> +			       (void *)READ_ONCE_NOCHECK(regs->nip),
> +			       (void *)READ_ONCE_NOCHECK(lr));
>   			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 += $(kvm-book3s_64-builtin-objs-y)
> +
> +# KVM does a lot in real-mode, and 64-bit Book3S KASAN doesn't support that
> +ifdef CONFIG_PPC_BOOK3S_64
> +KASAN_SANITIZE := n
> +endif
> diff --git a/arch/powerpc/mm/book3s64/Makefile b/arch/powerpc/mm/book3s64/Makefile
> index fd393b8be14f..41a86d2c7da4 100644
> --- a/arch/powerpc/mm/book3s64/Makefile
> +++ b/arch/powerpc/mm/book3s64/Makefile
> @@ -21,3 +21,11 @@ obj-$(CONFIG_PPC_MEM_KEYS)	+= 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
> 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..b26ada73215d
> --- /dev/null
> +++ b/arch/powerpc/mm/kasan/init_book3s_64.c
> @@ -0,0 +1,98 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KASAN for 64-bit Book3S powerpc
> + *
> + * Copyright (C) 2019-2020 IBM Corporation
> + * Author: Daniel Axtens <dja@...ens.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) {
> +		map_kernel_page(k_cur, __pa(va), PAGE_KERNEL);
> +		va += PAGE_SIZE;
> +	}

What about:

	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);
> +	}

No need of { } for single line loops. Check the kernel codyign stype


> +
> +	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

Why do you need that ? When PTEs are all pointing to the same page, it shoud already appear in a 
single line into []

> +
>   	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 c194c4ae8bc7..b6eb8ec1e5ad 100644
> --- a/arch/powerpc/platforms/Kconfig.cputype
> +++ b/arch/powerpc/platforms/Kconfig.cputype
> @@ -92,6 +92,7 @@ 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
> 

Christophe

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