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

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2021/6/9 14:17, Liu Shixin wrote:
> Hi, everybody,
>
> I perfected the patch based on the previous advice. How about this version?
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>
> 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@huawei.com>
>> ---
>> 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);
>>   }
>>   
>
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