Re: [PATCH 3/4] ARM: Support KFENCE for ARM

[ownia <ownia.linux@gmail.com>]

On 2021/8/25 17:21, Kefeng Wang wrote:
> Add architecture specific implementation details for KFENCE and enable
> KFENCE on ARM. In particular, this implements the required interface in
>  <asm/kfence.h>.
>
> KFENCE requires that attributes for pages from its memory pool can
> individually be set. Therefore, force the kfence pool to be mapped
> at page granularity.
>
> Testing this patch using the testcases in kfence_test.c and all passed
> with or without ARM_LPAE.
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>  arch/arm/Kconfig              |  1 +
>  arch/arm/include/asm/kfence.h | 52 +++++++++++++++++++++++++++++++++++
>  arch/arm/mm/fault.c           |  9 ++++--
>  3 files changed, 60 insertions(+), 2 deletions(-)
>  create mode 100644 arch/arm/include/asm/kfence.h
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 7a8059ff6bb0..3798f82a0c0d 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -73,6 +73,7 @@ config ARM
>  	select HAVE_ARCH_AUDITSYSCALL if AEABI && !OABI_COMPAT
>  	select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6
>  	select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU
> +	select HAVE_ARCH_KFENCE if MMU
>  	select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU
>  	select HAVE_ARCH_KASAN if MMU && !XIP_KERNEL
>  	select HAVE_ARCH_MMAP_RND_BITS if MMU
> diff --git a/arch/arm/include/asm/kfence.h b/arch/arm/include/asm/kfence.h
> new file mode 100644
> index 000000000000..eae7a12ab2a9
> --- /dev/null
> +++ b/arch/arm/include/asm/kfence.h
> @@ -0,0 +1,52 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef __ASM_ARM_KFENCE_H
> +#define __ASM_ARM_KFENCE_H
> +
> +#include <linux/kfence.h>
> +#include <asm/set_memory.h>
> +#include <asm/pgalloc.h>
> +
> +static inline int split_pmd_page(pmd_t *pmd, unsigned long addr)
> +{
> +	int i;
> +	unsigned long pfn = PFN_DOWN(__pa((addr & PMD_MASK)));
> +	pte_t *pte = pte_alloc_one_kernel(&init_mm);
> +
> +	if (!pte)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < PTRS_PER_PTE; i++)
> +		set_pte_ext(pte + i, pfn_pte(pfn + i, PAGE_KERNEL), 0);
> +	pmd_populate_kernel(&init_mm, pmd, pte);
> +
> +	flush_tlb_kernel_range(addr, addr + PMD_SIZE);
> +	return 0;
> +}
> +
> +static inline bool arch_kfence_init_pool(void)
> +{
> +	unsigned long addr;
> +	pmd_t *pmd;
> +
> +	for (addr = (unsigned long)__kfence_pool; is_kfence_address((void *)addr);
> +	     addr += PAGE_SIZE) {
> +		pmd = pmd_off_k(addr);
> +
> +		if (pmd_leaf(*pmd)) {
> +			if (split_pmd_page(pmd, addr))
> +				return false;
> +		}
> +	}
> +
> +	return true;
> +}
> +
> +static inline bool kfence_protect_page(unsigned long addr, bool protect)
> +{
> +	set_memory_valid(addr, 1, !protect);
> +
> +	return true;
> +}
> +
> +#endif /* __ASM_ARM_KFENCE_H */
> diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
> index f7ab6dabe89f..9fa221ffa1b9 100644
> --- a/arch/arm/mm/fault.c
> +++ b/arch/arm/mm/fault.c
> @@ -17,6 +17,7 @@
>  #include <linux/sched/debug.h>
>  #include <linux/highmem.h>
>  #include <linux/perf_event.h>
> +#include <linux/kfence.h>
>  
>  #include <asm/system_misc.h>
>  #include <asm/system_info.h>
> @@ -131,10 +132,14 @@ __do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
>  	/*
>  	 * No handler, we'll have to terminate things with extreme prejudice.
>  	 */
> -	if (addr < PAGE_SIZE)
> +	if (addr < PAGE_SIZE) {
>  		msg = "NULL pointer dereference";
> -	else
> +	} else {
> +		if (kfence_handle_page_fault(addr, is_write_fault(fsr), regs))
> +			return;
> +
>  		msg = "paging request";
> +	}


I think here should do some fixup to follow upstream mainline code.


>  
>  	die_kernel_fault(msg, mm, addr, fsr, regs);
>  }

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