linux-kernel - Re: [PATCH v2] hugetlb: clean up potential spectre issue warnings

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Date:   Mon, 21 Feb 2022 12:24:25 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Zhenguo Yao <yaozhenguo1@...il.com>,
        Liu Yuntao <liuyuntao10@...wei.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] hugetlb: clean up potential spectre issue warnings

On 2/21/22 00:42, Michal Hocko wrote:
> On Fri 18-02-22 13:29:46, Mike Kravetz wrote:
> [...]
>> @@ -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 >= MAX_NUMNODES)
>>  				break;
>> +			nid = array_index_nospec(tmp, MAX_NUMNODES);
>>  
>>  			s += count + 1;
>>  			tmp = memparse(s, &s);
> 
> This is an early boot code, how is this supposed to be used as a side
> channel?

I do not have an evil hacker mind, but I can not think of a way this one time
use of a user specified index could be an issue.  It does add noise to the
BUILD REGRESSION emails sent to Andrew.

-- 
Mike Kravetz