linux-kernel - Re: [PATCH v1 2/5] s390/uv: convert gmap_make

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: Fri, 5 Apr 2024 09:09:30 +0200
From: David Hildenbrand <david@...hat.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-s390@...r.kernel.org, kvm@...r.kernel.org,
 Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>,
 Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
 Thomas Huth <thuth@...hat.com>
Subject: Re: [PATCH v1 2/5] s390/uv: convert gmap_make_secure() to work on
 folios

On 05.04.24 05:29, Matthew Wilcox wrote:
> On Thu, Apr 04, 2024 at 06:36:39PM +0200, David Hildenbrand wrote:
>> +		/* We might get PTE-mapped large folios; split them first. */
>> +		if (folio_test_large(folio)) {
>> +			rc = -E2BIG;
> 
> We agree to this point.  I just turned this into -EINVAL.
> 
>>   
>> +	if (rc == -E2BIG) {
>> +		/*
>> +		 * Splitting might fail with -EBUSY due to unexpected folio
>> +		 * references, just like make_folio_secure(). So handle it
>> +		 * ahead of time without the PTL being held.
>> +		 */
>> +		folio_lock(folio);
>> +		rc = split_folio(folio);
>> +		folio_unlock(folio);
>> +		folio_put(folio);
>> +	}
> 
> Ummm ... if split_folio() succeeds, aren't we going to return 0 from
> this function, which will be interpreted as make_folio_secure() having
> succeeded?

I assume the code would have to handle that, because it must deal with 
possible races that would try to convert the folio page.

But the right thing to do is

if (!rc)
	goto again;

after the put.

-- 
Cheers,

David / dhildenb