Re: [PATCHv2 1/4] x86/mm/ident_map: Fix virtual address wrap to zero

[Tom Lendacky]

On 8/14/24 07:46, Kirill A. Shutemov wrote:
> Calculation of 'next' virtual address doesn't protect against wrapping
> to zero. It can result in page table corruption and hang. The
> problematic case is possible if user sets high x86_mapping_info::offset.
> 
> Replace manual 'next' calculation with p?d_addr_end() which handles
> wrapping correctly.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>

Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>

> ---
>  arch/x86/mm/ident_map.c | 14 +++-----------
>  1 file changed, 3 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c
> index 437e96fb4977..5872f3ee863c 100644
> --- a/arch/x86/mm/ident_map.c
> +++ b/arch/x86/mm/ident_map.c
> @@ -101,9 +101,7 @@ static int ident_pud_init(struct x86_mapping_info *info, pud_t *pud_page,
>  		pmd_t *pmd;
>  		bool use_gbpage;
>  
> -		next = (addr & PUD_MASK) + PUD_SIZE;
> -		if (next > end)
> -			next = end;
> +		next = pud_addr_end(addr, end);
>  
>  		/* if this is already a gbpage, this portion is already mapped */
>  		if (pud_leaf(*pud))
> @@ -154,10 +152,7 @@ static int ident_p4d_init(struct x86_mapping_info *info, p4d_t *p4d_page,
>  		p4d_t *p4d = p4d_page + p4d_index(addr);
>  		pud_t *pud;
>  
> -		next = (addr & P4D_MASK) + P4D_SIZE;
> -		if (next > end)
> -			next = end;
> -
> +		next = p4d_addr_end(addr, end);
>  		if (p4d_present(*p4d)) {
>  			pud = pud_offset(p4d, 0);
>  			result = ident_pud_init(info, pud, addr, next);
> @@ -199,10 +194,7 @@ int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
>  		pgd_t *pgd = pgd_page + pgd_index(addr);
>  		p4d_t *p4d;
>  
> -		next = (addr & PGDIR_MASK) + PGDIR_SIZE;
> -		if (next > end)
> -			next = end;
> -
> +		next = pgd_addr_end(addr, end);
>  		if (pgd_present(*pgd)) {
>  			p4d = p4d_offset(pgd, 0);
>  			result = ident_p4d_init(info, p4d, addr, next);