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

[Dan Carpenter <dan.carpenter@oracle.com>]

On Fri, Feb 18, 2022 at 11:40:25AM +0800, liuyuntao wrote:
> 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@oracle.com>
> > ---
> >  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
> 

Smatch ignores checks for negative when it's part of a clamp test.  In
this situation the check for negative is obviously harmless so a warning
is a false positive.

If you wrote it the other way:

		if (tmp >= MAX_NUMNODES || tmp < 0)

then Smatch would print a warning because I try not to get involved with
style debates but I really don't like that style...  :P

regards,
dan carpenter