linux-kernel - Re: [RFC][PATCH 04/10] x86/espfix: use kernel-default PTE mask

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: <f90cef60-1710-1d99-61ee-4527067b115f@linux.intel.com>
Date:   Thu, 22 Feb 2018 13:30:01 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Nadav Amit <namit@...are.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "aarcange@...hat.com" <aarcange@...hat.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "keescook@...gle.com" <keescook@...gle.com>,
        "hughd@...gle.com" <hughd@...gle.com>,
        "jgross@...e.com" <jgross@...e.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [RFC][PATCH 04/10] x86/espfix: use kernel-default PTE mask

On 02/22/2018 01:27 PM, Nadav Amit wrote:
> Dave Hansen <dave.hansen@...ux.intel.com> wrote:
>> From: Dave Hansen <dave.hansen@...ux.intel.com>
>> In creating its page tables, the espfix code masks its PGTABLE_PROT
>> value with the supported mask: __supported_pte_mask.  This ensures
>> that unsupported bits are not set in the final PTE.  But, it also
>> sets _PAGE_GLOBAL which we do not want for PTE.  Use
>> __default_kernel_pte_mask instead which clears _PAGE_GLOBAL for PTI.
> 
> Can you please explain what is your concern? Exposing more gadgets for
> speculative ROP attacks?
> 
> Or is it a general rule of not exposing any kernel code &data more than
> absolutely necessary?

I think it's good practice to just expose only the *minimal* amount of
data necessary.  It's easier to audit and less likely to expose things
accidentall.