Re: [PATCH v11 02/13] mm: apply_to_pte_range warn and fail if a large pte is encountered

[Miaohe Lin <linmiaohe@huawei.com>]

Hi:
On 2021/1/26 12:44, Nicholas Piggin wrote:
> apply_to_pte_range might mistake a large pte for bad, or treat it as a
> page table, resulting in a crash or corruption. Add a test to warn and
> return error if large entries are found.
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  mm/memory.c | 66 +++++++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 49 insertions(+), 17 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index feff48e1465a..672e39a72788 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2440,13 +2440,21 @@ static int apply_to_pmd_range(struct mm_struct *mm, pud_t *pud,
>  	}
>  	do {
>  		next = pmd_addr_end(addr, end);
> -		if (create || !pmd_none_or_clear_bad(pmd)) {
> -			err = apply_to_pte_range(mm, pmd, addr, next, fn, data,
> -						 create, mask);
> -			if (err)
> -				break;
> +		if (pmd_none(*pmd) && !create)
> +			continue;
> +		if (WARN_ON_ONCE(pmd_leaf(*pmd)))
> +			return -EINVAL;
> +		if (!pmd_none(*pmd) && WARN_ON_ONCE(pmd_bad(*pmd))) {
> +			if (!create)
> +				continue;
> +			pmd_clear_bad(pmd);
>  		}
> +		err = apply_to_pte_range(mm, pmd, addr, next,
> +					 fn, data, create, mask);
> +		if (err)
> +			break;
>  	} while (pmd++, addr = next, addr != end);
> +
>  	return err;
>  }
>  
> @@ -2468,13 +2476,21 @@ static int apply_to_pud_range(struct mm_struct *mm, p4d_t *p4d,
>  	}
>  	do {
>  		next = pud_addr_end(addr, end);
> -		if (create || !pud_none_or_clear_bad(pud)) {
> -			err = apply_to_pmd_range(mm, pud, addr, next, fn, data,
> -						 create, mask);
> -			if (err)
> -				break;
> +		if (pud_none(*pud) && !create)
> +			continue;
> +		if (WARN_ON_ONCE(pud_leaf(*pud)))
> +			return -EINVAL;
> +		if (!pud_none(*pud) && WARN_ON_ONCE(pud_bad(*pud))) {
> +			if (!create)
> +				continue;
> +			pud_clear_bad(pud);
>  		}
> +		err = apply_to_pmd_range(mm, pud, addr, next,
> +					 fn, data, create, mask);
> +		if (err)
> +			break;
>  	} while (pud++, addr = next, addr != end);
> +
>  	return err;
>  }
>  
> @@ -2496,13 +2512,21 @@ static int apply_to_p4d_range(struct mm_struct *mm, pgd_t *pgd,
>  	}
>  	do {
>  		next = p4d_addr_end(addr, end);
> -		if (create || !p4d_none_or_clear_bad(p4d)) {
> -			err = apply_to_pud_range(mm, p4d, addr, next, fn, data,
> -						 create, mask);
> -			if (err)
> -				break;
> +		if (p4d_none(*p4d) && !create)
> +			continue;
> +		if (WARN_ON_ONCE(p4d_leaf(*p4d)))
> +			return -EINVAL;
> +		if (!p4d_none(*p4d) && WARN_ON_ONCE(p4d_bad(*p4d))) {
> +			if (!create)
> +				continue;
> +			p4d_clear_bad(p4d);
>  		}
> +		err = apply_to_pud_range(mm, p4d, addr, next,
> +					 fn, data, create, mask);
> +		if (err)
> +			break;
>  	} while (p4d++, addr = next, addr != end);
> +
>  	return err;
>  }
>  
> @@ -2522,9 +2546,17 @@ static int __apply_to_page_range(struct mm_struct *mm, unsigned long addr,
>  	pgd = pgd_offset(mm, addr);
>  	do {
>  		next = pgd_addr_end(addr, end);
> -		if (!create && pgd_none_or_clear_bad(pgd))
> +		if (pgd_none(*pgd) && !create)
>  			continue;
> -		err = apply_to_p4d_range(mm, pgd, addr, next, fn, data, create, &mask);
> +		if (WARN_ON_ONCE(pgd_leaf(*pgd)))
> +			return -EINVAL;
> +		if (!pgd_none(*pgd) && WARN_ON_ONCE(pgd_bad(*pgd))) {
> +			if (!create)
> +				continue;
> +			pgd_clear_bad(pgd);
> +		}
> +		err = apply_to_p4d_range(mm, pgd, addr, next,
> +					 fn, data, create, &mask);
>  		if (err)
>  			break;
>  	} while (pgd++, addr = next, addr != end);
> 

Looks good to me, thanks.

Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>