linux-kernel - Re: 4.4-rc5: ugly warn on: 5 W+X pages found

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]

Message-ID: <CALCETrW60DfZs-v_W46sYFUmBXspa3BXWY-=dpuSF9iMaeLGFQ@mail.gmail.com>
Date:	Mon, 14 Dec 2015 14:25:10 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Pavel Machek <pavel@....cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	kernel list <linux-kernel@...r.kernel.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Peter Anvin <hpa@...or.com>, Mike Galbraith <efault@....de>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: 4.4-rc5: ugly warn on: 5 W+X pages found

On Mon, Dec 14, 2015 at 1:24 PM, Arjan van de Ven <arjan@...ux.intel.com> wrote:
>
>> That's weird.  The only API to do that seems to be manually setting
>> kmap_prot to _PAGE_KERNEL_EXEC, and nothing does that.  (Why is
>> kmap_prot a variable on x86 at all?  It has exactly one writer, and
>> that's the code that initializes it in the first place.  Shouldn't we
>> #define kmap_prot _PAGE_KERNEL?
>
>
> iirc it changes based on runtime detection of NX capability
>

Maybe it did, but if it still does, I can't find the code.

What *does* change is __supported_pte_mask.  If we're willing to make
disable_nx work a little less well, we could try to initialize
__supported_pte_mask from the very beginning.  (We currently seem to
detect and enable NX even before we enable paging.)  I suspect that
Pavel is seeing a kmap mapping left over from so early that it didn't
have NX set (killed by massage_pgprot).

Borislav, could we do that?  (Why do we have disable_nx at all?  I
suspect it was for debugging a long, long time ago.)

Alternatively, we could go through and set NX everywhere after we
decide we have NX, but that seems rather error-prone.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/