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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 23 Feb 2022 09:35:43 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     "Schaufler, Casey" <casey.schaufler@...el.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Zhenguo Yao <yaozhenguo1@...il.com>,
        Liu Yuntao <liuyuntao10@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "casey@...aufler-ca.com" <casey@...aufler-ca.com>
Subject: Re: [PATCH v2] hugetlb: clean up potential spectre issue warnings

On Tue 22-02-22 19:36:10, Dan Carpenter wrote:
> On Tue, Feb 22, 2022 at 04:15:45PM +0000, Schaufler, Casey wrote:
> > > -----Original Message-----
> > > From: Michal Hocko <mhocko@...e.com>
> > > Sent: Monday, February 21, 2022 11:48 PM
> > > To: Mike Kravetz <mike.kravetz@...cle.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 Mon 21-02-22 12:24:25, Mike Kravetz wrote:
> > > > 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.
> > > 
> > > Maybe Smack can be taught to ignore __init and other early boot
> > > functions.
> > 
> > Why is Smack getting called out? The relationship is not obvious.
> > 
> 
> He meant Smatch.  It's a really common mistake that I did not anticipate
> in 2002.

Right. My bad.

> I can probably silence the spectre warnings for __init functions.  TBH,
> I don't really understand spectre at all so I mostly ignore those
> warnings.  :/

AFAIU the spectre gadget would need to be called repeatedly to be usable
for a side channel attack. I might be really missing some scenario but
to me it seems that __init functions cannot really be used for that.
-- 
Michal Hocko
SUSE Labs