Re: [PATCH] hugetlb: clean up potential spectre issue warnings

[liuyuntao]

On 17 Feb 2022 15:42:18 -0800, Mike Kravetz wrote:
> Recently introduced code allows numa nodes to be specified on the
> kernel command line for hugetlb allocations or CMA reservations.  The
> node values are user specified and used as indicies into arrays.  This
> generated the following smatch warnings:
> 
> mm/hugetlb.c:4170 hugepages_setup() warn: potential spectre issue 'default_hugepages_in_node' [w]
> mm/hugetlb.c:4172 hugepages_setup() warn: potential spectre issue 'parsed_hstate->max_huge_pages_node' [w]
> mm/hugetlb.c:6898 cmdline_parse_hugetlb_cma() warn: potential spectre issue 'hugetlb_cma_size_in_node' [w] (local cap)
> 
> Clean up by using array_index_nospec to sanitize array indicies.
> 
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> ---
>  mm/hugetlb.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 1f0cca036f7f..6b14d0791cb4 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -31,6 +31,7 @@
>  #include <linux/llist.h>
>  #include <linux/cma.h>
>  #include <linux/migrate.h>
> +#include <linux/nospec.h>
>  
>  #include <asm/page.h>
>  #include <asm/pgalloc.h>
> @@ -4161,7 +4162,7 @@ static int __init hugepages_setup(char *s)
>  			}
>  			if (tmp >= nr_online_nodes)
>  				goto invalid;
> -			node = tmp;
> +			node = array_index_nospec(tmp, nr_online_nodes);
>  			p += count + 1;
>  			/* Parse hugepages */
>  			if (sscanf(p, "%lu%n", &tmp, &count) != 1)
> @@ -6889,9 +6890,9 @@ static int __init cmdline_parse_hugetlb_cma(char *p)
>  			break;
>  
>  		if (s[count] == ':') {
> -			nid = tmp;
> -			if (nid < 0 || nid >= MAX_NUMNODES)
> +			if (tmp < 0 || tmp >= MAX_NUMNODES)

Here tmp is unsigned, no need to check if less than 0.
Do we really have any automated checking? lol

>  				break;
> +			nid = array_index_nospec(tmp, MAX_NUMNODES);
>  
>  			s += count + 1;
>  			tmp = memparse(s, &s);
> -- 
> 2.34.1