Re: [PATCH -next] riscv: Enable KFENCE for riscv64

[Liu Shixin]

Hi, everybody,

I perfected the patch based on the previous advice. How about this version?


Thanks,


On 2021/5/29 16:03, Liu Shixin wrote:
> Add architecture specific implementation details for KFENCE and enable
> KFENCE for the riscv64 architecture. 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.
>
> Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
> ---
> 1. Add helper function split_pmd_page() which is used to split a pmd to ptes. 
> 2. Add the judgment on the result of pte_alloc_one_kernel().
>
>  arch/riscv/Kconfig              |  1 +
>  arch/riscv/include/asm/kfence.h | 63 +++++++++++++++++++++++++++++++++
>  arch/riscv/mm/fault.c           | 11 +++++-
>  3 files changed, 74 insertions(+), 1 deletion(-)
>  create mode 100644 arch/riscv/include/asm/kfence.h
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 4982130064ef..2f4903a7730f 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -65,6 +65,7 @@ config RISCV
>  	select HAVE_ARCH_JUMP_LABEL_RELATIVE
>  	select HAVE_ARCH_KASAN if MMU && 64BIT
>  	select HAVE_ARCH_KASAN_VMALLOC if MMU && 64BIT
> +	select HAVE_ARCH_KFENCE if MMU && 64BIT
>  	select HAVE_ARCH_KGDB
>  	select HAVE_ARCH_KGDB_QXFER_PKT
>  	select HAVE_ARCH_MMAP_RND_BITS if MMU
> diff --git a/arch/riscv/include/asm/kfence.h b/arch/riscv/include/asm/kfence.h
> new file mode 100644
> index 000000000000..d887a54042aa
> --- /dev/null
> +++ b/arch/riscv/include/asm/kfence.h
> @@ -0,0 +1,63 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _ASM_RISCV_KFENCE_H
> +#define _ASM_RISCV_KFENCE_H
> +
> +#include <linux/kfence.h>
> +#include <linux/pfn.h>
> +#include <asm-generic/pgalloc.h>
> +#include <asm/pgtable.h>
> +
> +static inline int split_pmd_page(unsigned long addr)
> +{
> +	int i;
> +	unsigned long pfn = PFN_DOWN(__pa((addr & PMD_MASK)));
> +	pmd_t *pmd = pmd_off_k(addr);
> +	pte_t *pte = pte_alloc_one_kernel(&init_mm);
> +
> +	if (!pte)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < PTRS_PER_PTE; i++)
> +		set_pte(pte + i, pfn_pte(pfn + i, PAGE_KERNEL));
> +	set_pmd(pmd, pfn_pmd(PFN_DOWN(__pa(pte)), PAGE_TABLE));
> +
> +	flush_tlb_kernel_range(addr, addr + PMD_SIZE);
> +	return 0;
> +}
> +
> +static inline bool arch_kfence_init_pool(void)
> +{
> +	int ret;
> +	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)) {
> +			ret = split_pmd_page(addr);
> +			if (ret)
> +				return false;
> +		}
> +	}
> +
> +	return true;
> +}
> +
> +static inline bool kfence_protect_page(unsigned long addr, bool protect)
> +{
> +	pte_t *pte = virt_to_kpte(addr);
> +
> +	if (protect)
> +		set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_PRESENT));
> +	else
> +		set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT));
> +
> +	flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> +
> +	return true;
> +}
> +
> +#endif /* _ASM_RISCV_KFENCE_H */
> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> index 096463cc6fff..aa08dd2f8fae 100644
> --- a/arch/riscv/mm/fault.c
> +++ b/arch/riscv/mm/fault.c
> @@ -14,6 +14,7 @@
>  #include <linux/signal.h>
>  #include <linux/uaccess.h>
>  #include <linux/kprobes.h>
> +#include <linux/kfence.h>
>  
>  #include <asm/ptrace.h>
>  #include <asm/tlbflush.h>
> @@ -45,7 +46,15 @@ static inline void no_context(struct pt_regs *regs, unsigned long addr)
>  	 * Oops. The kernel tried to access some bad page. We'll have to
>  	 * terminate things with extreme prejudice.
>  	 */
> -	msg = (addr < PAGE_SIZE) ? "NULL pointer dereference" : "paging request";
> +	if (addr < PAGE_SIZE)
> +		msg = "NULL pointer dereference";
> +	else {
> +		if (kfence_handle_page_fault(addr, regs->cause == EXC_STORE_PAGE_FAULT, regs))
> +			return;
> +
> +		msg = "paging request";
> +	}
> +
>  	die_kernel_fault(msg, addr, regs);
>  }
>