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SubjectRe: [PATCH v2 4/4] powerpc: Book3S 64-bit "heavyweight" KASAN support
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Le 10/12/2019 à 05:47, Daniel Axtens a écrit :
> KASAN support on powerpc64 is challenging:
>
> - We want to be able to support inline instrumentation so as to be
> able to catch global and stack issues.
>
> - We run some code in real mode after boot, most notably a lot of
> KVM code. We'd like to be able to instrument this.
>
> [For those not immersed in ppc64, in real mode, the top nibble or
> 2 bits (depending on radix/hash mmu) of the address is ignored. The
> linear mapping is placed at 0xc000000000000000. This means that a
> pointer to part of the linear mapping will work both in real mode,
> where it will be interpreted as a physical address of the form
> 0x000..., and out of real mode, where it will go via the linear
> mapping.]
>
> - Inline instrumentation requires a fixed offset.
>
> - Because of our running things in real mode, the offset has to
> point to valid memory both in and out of real mode.
>
> This makes finding somewhere to put the KASAN shadow region challenging.
>
> One approach is just to give up on inline instrumentation and override
> the address->shadow calculation. This way we can delay all checking
> until after we get everything set up to our satisfaction. However,
> we'd really like to do better.

I think all the 'we' wordings should be rephrased in line with kernel
process (see
https://www.kernel.org/doc/html/latest/process/submitting-patches.html):

Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
to do frotz", as if you are giving orders to the codebase to change
its behaviour.

For instance, could instead be:
"This way all checking can be delay after everything get set up to
satisfaction. However, better could really be done."


>
> What we can do - if we know _at compile time_ how much contiguous
> physical memory we have - is to set aside the top 1/8th of the memory
> and use that. This is a big hammer (hence the "heavyweight" name) and
> comes with 3 big consequences:
>
> - kernels will simply fail to boot on machines with less memory than
> specified when compiling.
>
> - kernels running on machines with more memory than specified when
> compiling will simply ignore the extra memory.
>
> - there's no nice way to handle physically discontiguous memory, so
> you are restricted to the first physical memory block.
>
> If you can bear all this, you get full support for KASAN.
>
> Despite the limitations, it can still find bugs,
> e.g. http://patchwork.ozlabs.org/patch/1103775/
>
> The current implementation is Radix only.
>
> Massive thanks to mpe, who had the idea for the initial design.
>
> Signed-off-by: Daniel Axtens <dja@axtens.net>
>
> ---
> Changes since v1:
> - Landed kasan vmalloc support upstream
> - Lots of feedback from Christophe.
>
> Changes since the rfc:
>
> - Boots real and virtual hardware, kvm works.
>
> - disabled reporting when we're checking the stack for exception
> frames. The behaviour isn't wrong, just incompatible with KASAN.
>
> - Documentation!
>
> - Dropped old module stuff in favour of KASAN_VMALLOC.
>
> The bugs with ftrace and kuap were due to kernel bloat pushing
> prom_init calls to be done via the plt. Because we did not have
> a relocatable kernel, and they are done very early, this caused
> everything to explode. Compile with CONFIG_RELOCATABLE!
> ---
> Documentation/dev-tools/kasan.rst | 8 +-
> Documentation/powerpc/kasan.txt | 102 +++++++++++++++++-
> arch/powerpc/Kconfig | 3 +
> arch/powerpc/Kconfig.debug | 21 ++++
> arch/powerpc/Makefile | 11 ++
> arch/powerpc/include/asm/kasan.h | 20 +++-
> arch/powerpc/kernel/process.c | 8 ++
> arch/powerpc/kernel/prom.c | 59 +++++++++-
> arch/powerpc/mm/kasan/Makefile | 3 +-
> .../mm/kasan/{kasan_init_32.c => init_32.c} | 0
> arch/powerpc/mm/kasan/init_book3s_64.c | 67 ++++++++++++
> 11 files changed, 293 insertions(+), 9 deletions(-)
> rename arch/powerpc/mm/kasan/{kasan_init_32.c => init_32.c} (100%)
> 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 4af2b5d2c9b4..d99dc580bc11 100644
> --- a/Documentation/dev-tools/kasan.rst
> +++ b/Documentation/dev-tools/kasan.rst
> @@ -22,8 +22,9 @@ global variables yet.
> Tag-based KASAN is only supported in Clang and requires version 7.0.0 or later.
>
> Currently generic KASAN is supported for the x86_64, arm64, xtensa and s390
> -architectures. It is also supported on 32-bit powerpc kernels. Tag-based KASAN
> -is supported only on arm64.
> +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
> -----
> @@ -256,7 +257,8 @@ 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 is optional on x86, and
> +required on 64-bit powerpc.
>
> 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 a85ce2ff8244..d6e7a415195c 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 64-bit Radix only.

May be understood as : KASAN is supported on powerpc on 32-bit Radix and
64-bit Radix only.
Maybe would be more clear as : KASAN is supported on powerpc on 32-bit
and Radix 64-bit only.

>
> 32 bit support
> ==============
> @@ -10,3 +10,103 @@ fixmap area and occupies one eighth of the total kernel virtual memory space.
>
> Instrumentation of the vmalloc area is not currently supported, but modules
> are.
> +
> +64 bit support
> +==============

A lot of 'we' form here as well. Can it be avoided ?

> +
> +Currently, only the radix MMU is supported. There have been versions for Book3E
> +processors floating around on the mailing list, but nothing has been merged.
> +
> +KASAN support on Book3S is a bit tricky to get right:
> +
> + - We want to be able to support inline instrumentation so as to be able to
> + catch global and stack issues.
> +
> + - Inline instrumentation requires a fixed offset.
> +
> + - We run a lot of code in real mode. Most notably a lot of KVM runs in real
> + mode, and we'd like to be able to instrument it.
> +
> + - Because we run code in real mode after boot, the offset has to point to
> + valid memory both in and out of real mode.
> +
> +One approach is just to give up on inline instrumentation. This way we can
> +delay all checks until after we get everything set up correctly. However, we'd
> +really like to do better.
> +
> +If we know _at compile time_ how much contiguous physical memory we have, we
> +can set aside the top 1/8th of the first block of physical memory and use
> +that. This is a big hammer and comes with 3 big consequences:
> +
> + - there's no nice way to handle physically discontiguous memory, so
> + you are restricted to the first physical memory block.
> +
> + - kernels will simply fail to boot on machines with less memory than specified
> + when compiling.
> +
> + - kernels running on machines with more memory than specified when compiling
> + will simply ignore the extra memory.
> +
> +If you can live with this, you get full support for KASAN.
> +
> +Tips
> +----
> +
> + - Compile with CONFIG_RELOCATABLE.
> +
> + In development, we found boot hangs when building with ftrace and KUAP
> + on. These ended up being due to kernel bloat pushing prom_init calls to be
> + done via the PLT. Because we did not have a relocatable kernel, and they are
> + done very early, this caused us to jump off into somewhere invalid. Enabling
> + relocation fixes this.
> +
> +NUMA/discontiguous physical memory
> +----------------------------------
> +
> +We currently cannot really deal with discontiguous physical memory. You are
> +restricted to the physical memory that is contiguous from physical address
> +zero, and must specify the size of that memory, not total memory, when
> +configuring your kernel.
> +
> +Discontiguous memory can occur when you have a machine with memory spread
> +across multiple nodes. For example, on a Talos II with 64GB of RAM:
> +
> + - 32GB runs from 0x0 to 0x0000_0008_0000_0000,
> + - then there's a gap,
> + - then the final 32GB runs from 0x0000_2000_0000_0000 to 0x0000_2008_0000_0000
> +
> +This can create _significant_ issues:
> +
> + - If we try to treat the machine as having 64GB of _contiguous_ RAM, we would
> + assume that ran from 0x0 to 0x0000_0010_0000_0000. We'd then reserve the
> + last 1/8th - 0x0000_000e_0000_0000 to 0x0000_0010_0000_0000 as the shadow
> + region. But when we try to access any of that, we'll try to access pages
> + that are not physically present.
> +
> + - If we try to base the shadow region size on the top address, we'll need to
> + reserve 0x2008_0000_0000 / 8 = 0x0401_0000_0000 bytes = 4100 GB of memory,
> + which will clearly not work on a system with 64GB of RAM.
> +
> +Therefore, you are restricted to the memory in the node starting at 0x0. For
> +this system, that's 32GB. If you specify a contiguous physical memory size
> +greater than the size of the first contiguous region of memory, the system will
> +be unable to boot or even print an error message warning you.
> +
> +You can determine the layout of your system's memory by observing the messages
> +that the Radix MMU prints on boot. The Talos II discussed earlier has:
> +
> +radix-mmu: Mapped 0x0000000000000000-0x0000000040000000 with 1.00 GiB pages (exec)
> +radix-mmu: Mapped 0x0000000040000000-0x0000000800000000 with 1.00 GiB pages
> +radix-mmu: Mapped 0x0000200000000000-0x0000200800000000 with 1.00 GiB pages
> +
> +As discussed, you'd configure this system for 32768 MB.
> +
> +Another system prints:
> +
> +radix-mmu: Mapped 0x0000000000000000-0x0000000040000000 with 1.00 GiB pages (exec)
> +radix-mmu: Mapped 0x0000000040000000-0x0000002000000000 with 1.00 GiB pages
> +radix-mmu: Mapped 0x0000200000000000-0x0000202000000000 with 1.00 GiB pages
> +
> +This machine has more memory: 0x0000_0040_0000_0000 total, but only
> +0x0000_0020_0000_0000 is physically contiguous from zero, so we'd configure the
> +kernel for 131072 MB of physically contiguous memory.
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 1ec34e16ed65..f68650f14e61 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -173,6 +173,9 @@ 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
> + select HAVE_ARCH_KASAN if PPC_BOOK3S_64 && PPC_RADIX_MMU
> + select HAVE_ARCH_KASAN_VMALLOC if PPC_BOOK3S_64

Does it mean, if PPC_RADIX_MMU, HAVE_ARCH_KASAN_VMALLOC will be defined
and not HAVE_ARCH_KASAN ?


> + select KASAN_VMALLOC if KASAN && PPC_BOOK3S_64
> 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 4e1d39847462..90bb48455cb8 100644
> --- a/arch/powerpc/Kconfig.debug
> +++ b/arch/powerpc/Kconfig.debug
> @@ -394,6 +394,27 @@ config PPC_FAST_ENDIAN_SWITCH
> help
> If you're unsure what this is, say N.
>
> +config PHYS_MEM_SIZE_FOR_KASAN
> + int "Contiguous physical memory size for KASAN (MB)" if KASAN && PPC_BOOK3S_64
> + default 0
> + help
> +
> + To get inline instrumentation support for KASAN on 64-bit Book3S
> + machines, you need to know how much contiguous physical memory your
> + system has. A shadow offset will be calculated based on this figure,
> + which will be compiled in to the kernel. KASAN will use this offset
> + to access its shadow region, which is used to verify memory accesses.
> +
> + If you attempt to boot on a system with less memory than you specify
> + here, your system will fail to boot very early in the process. If you
> + boot on a system with more memory than you specify, the extra memory
> + will wasted - it will be reserved and not used.
> +
> + For systems with discontiguous blocks of physical memory, specify the
> + size of the block starting at 0x0. You can determine this by looking
> + at the memory layout info printed to dmesg by the radix MMU code
> + early in boot. See Documentation/powerpc/kasan.txt.
> +
> config KASAN_SHADOW_OFFSET
> hex
> depends on KASAN
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index f35730548e42..eff693527462 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -230,6 +230,17 @@ ifdef CONFIG_476FPE_ERR46
> -T $(srctree)/arch/powerpc/platforms/44x/ppc476_modules.lds
> endif
>
> +ifdef CONFIG_PPC_BOOK3S_64
> +# The KASAN shadow offset is such that linear map (0xc000...) is shadowed by
> +# the last 8th of linearly mapped physical memory. This way, if the code uses
> +# 0xc addresses throughout, accesses work both in in real mode (where the top
> +# 2 bits are ignored) and outside of real mode.
> +#
> +# 0xc000000000000000 >> 3 = 0xa800000000000000 = 12105675798371893248
> +KASAN_SHADOW_OFFSET = $(shell echo 7 \* 1024 \* 1024 \* $(CONFIG_PHYS_MEM_SIZE_FOR_KASAN) / 8 + 12105675798371893248 | bc)
> +KBUILD_CFLAGS += -DKASAN_SHADOW_OFFSET=$(KASAN_SHADOW_OFFSET)UL
> +endif
> +
> # No AltiVec or VSX instructions when building kernel
> KBUILD_CFLAGS += $(call cc-option,-mno-altivec)
> KBUILD_CFLAGS += $(call cc-option,-mno-vsx)
> diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
> index 296e51c2f066..98d995bc9b5e 100644
> --- a/arch/powerpc/include/asm/kasan.h
> +++ b/arch/powerpc/include/asm/kasan.h
> @@ -14,13 +14,20 @@
>
> #ifndef __ASSEMBLY__
>
> -#include <asm/page.h>
> +#ifdef CONFIG_KASAN
> +void kasan_init(void);
> +#else
> +static inline void kasan_init(void) { }
> +#endif
>
> #define KASAN_SHADOW_SCALE_SHIFT 3
>
> #define KASAN_SHADOW_START (KASAN_SHADOW_OFFSET + \
> (PAGE_OFFSET >> KASAN_SHADOW_SCALE_SHIFT))
>
> +#ifdef CONFIG_PPC32
> +#include <asm/page.h>

Is that a problem to include page.h is not PPC32 ?

> +
> #define KASAN_SHADOW_OFFSET ASM_CONST(CONFIG_KASAN_SHADOW_OFFSET)
>
> #define KASAN_SHADOW_END 0UL
> @@ -30,11 +37,18 @@
> #ifdef CONFIG_KASAN
> void kasan_early_init(void);
> void kasan_mmu_init(void);
> -void kasan_init(void);
> #else
> -static inline void kasan_init(void) { }
> static inline void kasan_mmu_init(void) { }
> #endif
> +#endif
> +
> +#ifdef CONFIG_PPC_BOOK3S_64
> +#include <asm/pgtable.h>
> +
> +#define KASAN_SHADOW_SIZE ((u64)CONFIG_PHYS_MEM_SIZE_FOR_KASAN * \
> + 1024 * 1024 * 1 / 8)
> +
> +#endif /* CONFIG_PPC_BOOK3S_64 */
>
> #endif /* __ASSEMBLY */
> #endif
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index 4df94b6e2f32..c60ff299f39b 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -2081,7 +2081,14 @@ 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.
> + *
> + * KASAN may complain about this. If it is an exception frame,
> + * we won't have unpoisoned the stack in asm when we set the
> + * exception marker. If it's not an exception frame, who knows
> + * how things are laid out - the shadow could be in any state
> + * at all. Just disable KASAN reporting for now.
> */
> + kasan_disable_current();
> if (validate_sp(sp, tsk, STACK_INT_FRAME_SIZE)
> && stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
> struct pt_regs *regs = (struct pt_regs *)
> @@ -2091,6 +2098,7 @@ void show_stack(struct task_struct *tsk, unsigned long *stack)
> regs->trap, (void *)regs->nip, (void *)lr);
> firstframe = 1;
> }
> + kasan_enable_current();
>
> sp = newsp;
> } while (count++ < kstack_depth_to_print);
> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> index 6620f37abe73..b32036f61cad 100644
> --- a/arch/powerpc/kernel/prom.c
> +++ b/arch/powerpc/kernel/prom.c
> @@ -72,6 +72,7 @@ unsigned long tce_alloc_start, tce_alloc_end;
> u64 ppc64_rma_size;
> #endif
> static phys_addr_t first_memblock_size;
> +static phys_addr_t top_phys_addr;
> static int __initdata boot_cpu_count;
>
> static int __init early_parse_mem(char *p)
> @@ -449,6 +450,21 @@ static bool validate_mem_limit(u64 base, u64 *size)
> {
> u64 max_mem = 1UL << (MAX_PHYSMEM_BITS);
>
> +#ifdef CONFIG_KASAN

CONFIG_PHYS_MEM_SIZE_FOR_KASAN is know defined at all time, so this
ifdef can be avoided and replaced for instance by adding verification of
IS_ENABLED(CONFIG_KASAN) in the if() below.

> + /*
> + * To handle the NUMA/discontiguous memory case, don't allow a block
> + * to be added if it falls completely beyond the configured physical
> + * memory.
> + *
> + * See Documentation/powerpc/kasan.txt
> + */
> + if (base >= (u64)CONFIG_PHYS_MEM_SIZE_FOR_KASAN * 1024 * 1024) {
> + pr_warn("KASAN: not adding mem block at %llx (size %llx)",
> + base, *size);
> + return false;
> + }
> +#endif
> +
> if (base >= max_mem)
> return false;
> if ((base + *size) > max_mem)
> @@ -572,8 +588,11 @@ void __init early_init_dt_add_memory_arch(u64 base, u64 size)
>
> /* Add the chunk to the MEMBLOCK list */
> if (add_mem_to_memblock) {
> - if (validate_mem_limit(base, &size))
> + if (validate_mem_limit(base, &size)) {
> memblock_add(base, size);
> + if (base + size > top_phys_addr)
> + top_phys_addr = base + size;
> + }
> }
> }
>
> @@ -613,6 +632,8 @@ static void __init early_reserve_mem_dt(void)
> static void __init early_reserve_mem(void)
> {
> __be64 *reserve_map;
> + phys_addr_t kasan_shadow_start;
> + phys_addr_t kasan_memory_size;
>
> reserve_map = (__be64 *)(((unsigned long)initial_boot_params) +
> fdt_off_mem_rsvmap(initial_boot_params));
> @@ -651,6 +672,42 @@ static void __init early_reserve_mem(void)
> return;
> }
> #endif
> +
> + if (IS_ENABLED(CONFIG_KASAN) && IS_ENABLED(CONFIG_PPC_BOOK3S_64)) {
> + kasan_memory_size =
> + ((phys_addr_t)CONFIG_PHYS_MEM_SIZE_FOR_KASAN << 20);
> +
> + if (top_phys_addr < kasan_memory_size) {
> + /*
> + * We are doomed. Attempts to call e.g. panic() are
> + * likely to fail because they call out into
> + * instrumented code, which will almost certainly
> + * access memory beyond the end of physical
> + * memory. Hang here so that at least the NIP points
> + * somewhere that will help you debug it if you look at
> + * it in qemu.
> + */

This function is called from early_init_devtree() which also includes a
call to panic(). That panic call should be changed then ?

> + while (true)
> + ;

Can we trap instead, with BUG() or __builtin_trap() ?

Maybe define a function prom_panic() which calls panic() when
CONFIG_KASAN is not set, and does whatever works when CONFIG_KASAN is set ?


> + } else if (top_phys_addr > kasan_memory_size) {
> + /* print a biiiig warning in hopes people notice */
> + pr_err("===========================================\n"
> + "Physical memory exceeds compiled-in maximum!\n"
> + "This kernel was compiled for KASAN with %u MB physical memory.\n"
> + "The actual physical memory detected is %llu MB.\n"
> + "Memory above the compiled limit will not be used!\n"
> + "===========================================\n",
> + CONFIG_PHYS_MEM_SIZE_FOR_KASAN,
> + top_phys_addr / (1024 * 1024));
> + }
> +
> + kasan_shadow_start = _ALIGN_DOWN(kasan_memory_size * 7 / 8,
> + PAGE_SIZE);
> + DBG("reserving %llx -> %llx for KASAN",
> + kasan_shadow_start, top_phys_addr);
> + memblock_reserve(kasan_shadow_start,
> + top_phys_addr - kasan_shadow_start);
> + }
> }
> #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> diff --git a/arch/powerpc/mm/kasan/Makefile b/arch/powerpc/mm/kasan/Makefile
> index 6577897673dd..f02b15c78e4d 100644
> --- a/arch/powerpc/mm/kasan/Makefile
> +++ b/arch/powerpc/mm/kasan/Makefile
> @@ -2,4 +2,5 @@
>
> KASAN_SANITIZE := n
>
> -obj-$(CONFIG_PPC32) += kasan_init_32.o
> +obj-$(CONFIG_PPC32) += init_32.o
> +obj-$(CONFIG_PPC_BOOK3S_64) += init_book3s_64.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
> 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..43e9252c8bd3
> --- /dev/null
> +++ b/arch/powerpc/mm/kasan/init_book3s_64.c
> @@ -0,0 +1,67 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KASAN for 64-bit Book3S powerpc
> + *
> + * Copyright (C) 2019 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 <asm/pgalloc.h>
> +
> +void __init kasan_init(void)
> +{
> + int i;
> + void *k_start = kasan_mem_to_shadow((void *)RADIX_KERN_VIRT_START);
> + void *k_end = kasan_mem_to_shadow((void *)RADIX_VMEMMAP_END);
> +
> + pte_t pte = __pte(__pa(kasan_early_shadow_page) |
> + pgprot_val(PAGE_KERNEL) | _PAGE_PTE);
> +
> + if (!early_radix_enabled())
> + panic("KASAN requires radix!");
> +
> + for (i = 0; i < PTRS_PER_PTE; i++)
> + __set_pte_at(&init_mm, (unsigned long)kasan_early_shadow_page,
> + &kasan_early_shadow_pte[i], 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);
> +
> + memset(kasan_mem_to_shadow((void *)PAGE_OFFSET), KASAN_SHADOW_INIT,
> + KASAN_SHADOW_SIZE);
> +
> + kasan_populate_early_shadow(
> + kasan_mem_to_shadow((void *)RADIX_KERN_VIRT_START),
> + kasan_mem_to_shadow((void *)RADIX_VMALLOC_START));
> +
> + /* leave a hole here for vmalloc */
> +
> + kasan_populate_early_shadow(
> + kasan_mem_to_shadow((void *)RADIX_VMALLOC_END),
> + kasan_mem_to_shadow((void *)RADIX_VMEMMAP_END));
> +
> + flush_tlb_kernel_range((unsigned long)k_start, (unsigned long)k_end);
> +
> + /* mark early shadow region as RO and wipe */
> + pte = __pte(__pa(kasan_early_shadow_page) |
> + pgprot_val(PAGE_KERNEL_RO) | _PAGE_PTE);

Any reason for _PAGE_PTE being required here and not being included in
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], pte, 0);
> +
> + memset(kasan_early_shadow_page, 0, PAGE_SIZE);

Can use clear_page() instead ?

> +
> + /* Enable error messages */
> + init_task.kasan_depth = 0;
> + pr_info("KASAN init done (64-bit Book3S heavyweight mode)\n");
> +}
>


Christophe

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