linux-kernel - Re: [PATCH 00/23] KAISER: unmap most of the kernel from userspace page tables

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: <5005a38e-4dbf-d302-9a82-97c92d0f8f07@linux.intel.com>
Date:   Wed, 1 Nov 2017 11:46:31 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 00/23] KAISER: unmap most of the kernel from userspace
 page tables

On 11/01/2017 11:27 AM, Linus Torvalds wrote:
> So I'd like to see not just the comments about this, but I'd like to
> see the code itself actually making that very clear. Have *code* that
> verifies that nobody ever tries to use this on a user address (because
> that would *completely* screw up all coherency), but also I don't see
> why the code possibly looks up the old physical address in ther page
> table. Is there _any_ possible reason why you'd want to look up a page
> from an old page table? As far as I can tell, we should always know
> the physical page we are mapping a priori - we've never re-mapping
> random virtual addresses or a highmem page or anything like that.
> We're mapping the 1:1 kernel mapping only.

The vmalloc()'d stacks definitely need the page table walk.  That's yet
another thing that will get simpler once we stop needing to map the
process stacks.  I think there was also a need to do this for the fixmap
addresses for the GDT.

But, I'm totally with you on making this stuff less generic.