linux-kernel - Re: [tip:x86/mm] x86/mm: Consider effective protection attributes in W+X check

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:   Mon, 26 Feb 2018 03:08:45 -0700
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Andrey Ryabinin" <aryabinin@...tuozzo.com>
Cc:     <bp@...en8.de>, <brgerst@...il.com>, <dvyukov@...gle.com>,
        <glider@...gle.com>, <peterz@...radead.org>, <luto@...nel.org>,
        <mingo@...nel.org>, <tglx@...utronix.de>,
        <torvalds@...ux-foundation.org>, <boris.ostrovsky@...cle.com>,
        <dvlasenk@...hat.com>, <jpoimboe@...hat.com>,
        "Juergen Gross" <jgross@...e.com>, <linux-kernel@...r.kernel.org>,
        <linux-tip-commits@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [tip:x86/mm] x86/mm: Consider effective protection
 attributes in W+X check

>>> On 26.02.18 at 11:00, <aryabinin@...tuozzo.com> wrote:
> On 02/26/2018 11:48 AM, tip-bot for Jan Beulich wrote:
>> @@ -351,7 +362,7 @@ static inline bool kasan_page_table(struct seq_file *m, struct pg_state *st,
>>  	    (pgtable_l5_enabled && __pa(pt) == __pa(kasan_zero_p4d)) ||
>>  	    __pa(pt) == __pa(kasan_zero_pud)) {
>>  		pgprotval_t prot = pte_flags(kasan_zero_pte[0]);
>> -		note_page(m, st, __pgprot(prot), 5);
>> +		note_page(m, st, __pgprot(prot), 0, 5);
> 
> Isn't this disables W+X check for kasan page table?
> Methinks it should be 'prot' here.

Might well be - I actually did ask the question before sending v3,
but didn't get any answer (yet). The kasan_zero_p?d names
suggested to me that this is a shortcut for mappings which
otherwise would be non-present anyway, but that was merely a
guess. As to W+X checks - I can't see how the result could be
any better if the protections of kasan_zero_pte[0] would be
used: Those can't possibly be applicable independent of VA.

Jan