From: Dave Hansen <dave.hansen@linux.intel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Kees Cook <keescook@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Juergen Gross <jgross@suse.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Greg KH <gregkh@linuxfoundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Hugh Dickins <hughd@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Borislav Petkov <bp@alien8.de>, Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH 5/7] x86/mm/init: remove freed kernel image areas from alias mapping
Date: Mon, 6 Aug 2018 08:17:59 -0700 [thread overview]
Message-ID: <979a041c-f856-d95e-eeb1-1c086e447840@linux.intel.com> (raw)
In-Reply-To: <CALCETrV3O8WexN_zvksYWersyLu1K9GCiYJoLCB2-Jsxq9MGGQ@mail.gmail.com>
On 08/04/2018 02:38 PM, Andy Lutomirski wrote:
> On Thu, Aug 2, 2018 at 3:58 PM, Dave Hansen <dave.hansen@linux.intel.com> wrote:
>> This otherwise unused alias mapping of the holes will, by default
>> keep the Global bit, be mapped out to userspace, and be
>> vulnerable to Meltdown.
>>
>> Remove the alias mapping of these pages entirely. This is likely
>> to fracture the 2M page mapping the kernel image near these areas,
>> but this should affect a minority of the area.
...
>
> I like this patch, and I tend to think we should (eventually) enable
> it regardless of PTI. Cleaning up the memory map is generally a good
> thing.
>
> Also, just to make sure I fully understand: the kernel text is aliased
> in both the direct map and the high map, right?
Yes. I don't think the double mapping was because of anything that we
really intentionally designed, though. I think it was just easiest to
leave it in place and it didn't hurt anything.
> This means that we should be able to make the high kernel mapping
> have proper RO permissions very early without breaking text_poke() at
> the minor cost of needing to force a serializing instruction at the
> end of each big block of text pokes. I think this would be
> worthwhile, although I suspect we'll uncover *tons* of bugs in the
> process.
Yeah, this could easily happen much earlier.
next prev parent reply other threads:[~2018-08-06 15:18 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-02 22:58 [PATCH 0/7] [v2] x86/mm/pti: close two Meltdown leaks with Global kernel mapping Dave Hansen
2018-08-02 22:58 ` [PATCH 1/7] x86/mm/pti: clear Global bit more aggressively Dave Hansen
2018-08-05 20:30 ` [tip:x86/pti] x86/mm/pti: Clear " tip-bot for Dave Hansen
2018-08-02 22:58 ` [PATCH 2/7] mm: allow non-direct-map arguments to free_reserved_area() Dave Hansen
2018-08-05 20:31 ` [tip:x86/pti] mm: Allow " tip-bot for Dave Hansen
2018-08-02 22:58 ` [PATCH 3/7] x86/mm/init: pass unconverted symbol addresses to free_init_pages() Dave Hansen
2018-08-04 0:18 ` Hugh Dickins
2018-08-04 17:31 ` Linus Torvalds
2018-08-04 18:23 ` Hugh Dickins
2018-08-05 6:11 ` Andi Kleen
2018-08-05 20:31 ` [tip:x86/pti] x86/mm/init: Pass " tip-bot for Dave Hansen
2018-08-02 22:58 ` [PATCH 4/7] x86/mm/init: add helper for freeing kernel image pages Dave Hansen
2018-08-05 20:32 ` [tip:x86/pti] x86/mm/init: Add " tip-bot for Dave Hansen
2018-08-02 22:58 ` [PATCH 5/7] x86/mm/init: remove freed kernel image areas from alias mapping Dave Hansen
2018-08-04 0:35 ` Hugh Dickins
2018-08-04 21:38 ` Andy Lutomirski
2018-08-06 15:17 ` Dave Hansen [this message]
2018-08-05 20:32 ` [tip:x86/pti] x86/mm/init: Remove " tip-bot for Dave Hansen
2018-08-06 20:21 ` [tip:x86/pti-urgent] " tip-bot for Dave Hansen
2018-08-02 22:58 ` [PATCH 6/7] x86/mm/pageattr: pass named flag instead of 0/1 Dave Hansen
2018-08-05 20:09 ` Thomas Gleixner
2018-08-06 15:09 ` Dave Hansen
2018-08-02 22:58 ` [PATCH 7/7] x86/mm/pageattr: Remove implicit NX behavior Dave Hansen
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