Re: [PATCH RFC v2] riscv: Enable KFENCE for riscv64

[Marco Elver]

On Fri, 14 May 2021 at 05:11, Liu Shixin <liushixin2@xxxxxxxxxx> 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.
>
> I tested this patch using the testcases in kfence_test.c and all passed.
>
> Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>

Acked-by: Marco Elver <elver@xxxxxxxxxx>


> ---
> v1->v2: Change kmalloc() to pte_alloc_one_kernel() for allocating pte.
>
>  arch/riscv/Kconfig              |  1 +
>  arch/riscv/include/asm/kfence.h | 51 +++++++++++++++++++++++++++++++++
>  arch/riscv/mm/fault.c           | 11 ++++++-
>  3 files changed, 62 insertions(+), 1 deletion(-)
>  create mode 100644 arch/riscv/include/asm/kfence.h
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index c426e7d20907..000d8aba1030 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -64,6 +64,7 @@ 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..c25d67e0b8ba
> --- /dev/null
> +++ b/arch/riscv/include/asm/kfence.h
> @@ -0,0 +1,51 @@
> +/* 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 bool arch_kfence_init_pool(void)
> +{
> +       int i;
> +       unsigned long addr;
> +       pte_t *pte;
> +       pmd_t *pmd;
> +
> +       for (addr = (unsigned long)__kfence_pool; is_kfence_address((void *)addr);
> +            addr += PAGE_SIZE) {
> +               pte = virt_to_kpte(addr);
> +               pmd = pmd_off_k(addr);
> +
> +               if (!pmd_leaf(*pmd) && pte_present(*pte))
> +                       continue;
> +
> +               pte = pte_alloc_one_kernel(&init_mm);
> +               for (i = 0; i < PTRS_PER_PTE; i++)
> +                       set_pte(pte + i, pfn_pte(PFN_DOWN(__pa((addr & PMD_MASK) + i * PAGE_SIZE)), PAGE_KERNEL));
> +
> +               set_pmd(pmd, pfn_pmd(PFN_DOWN(__pa(pte)), PAGE_TABLE));
> +               flush_tlb_kernel_range(addr, addr + PMD_SIZE);
> +       }
> +
> +       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);
>  }
>
> --
> 2.18.0.huawei.25
>