Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Sat, 18 Nov 2017 00:20:56 -0800
From: Kees Cook <>
To: Linus Torvalds <>
Cc: Patrick McLean <>, Emese Revfy <>, 
	Al Viro <>, Bruce Fields <>, 
	"Darrick J. Wong" <>, 
	Linux Kernel Mailing List <>, 
	Linux NFS Mailing List <>, stable <>, 
	Thorsten Leemhuis <>, 
	"" <>
Subject: Re: [nfsd4] potentially hardware breaking regression in 4.14-rc and 4.13.11

On Fri, Nov 17, 2017 at 9:29 PM, Linus Torvalds
<> wrote:
> On Fri, Nov 17, 2017 at 9:14 PM, Kees Cook <> wrote:
>> FWIW, myself doing a build at d9e12200852d with and without
>> GCC_PLUGIN_RANDSTRUCT _appears_ to produce identical objdump output
>> where I did spot-checks.
> That would probably be a good thing to check anyway - check the
> difference between GCC_PLUGIN_RANDSTRUCT on and off at that commit.
> Just do
>    objdump --disassemble vmlinux > file
> and compare the two files for where the differences start occurring.

Yeah, I was just doing that now. Looks like there _is_ something
getting changed just from having the plugin enabled, but it appears
localized. For me, the first non-offset change happens in
lookup_user_key and persists for a while.

-ffffffff813893a7:      0f 85 55 03 00 00       jne
ffffffff81389702 <lookup_user_key+0x3f2>
-ffffffff813893ad:      f0 41 ff 06             lock incl (%r14)
-ffffffff813893b1:      83 fb 07                cmp    $0x7,%ebx
-ffffffff813893b4:      4c 89 b5 70 ff ff ff    mov    %r14,-0x90(%rbp)
+ffffffff813893a7:      0f 85 35 03 00 00       jne
ffffffff813896e2 <lookup_user_key+0x3d2>
+ffffffff813893ad:      4d 89 f0                mov    %r14,%r8
+ffffffff813893b0:      f0 41 ff 06             lock incl (%r14)
+ffffffff813893b4:      83 fb 07                cmp    $0x7,%ebx
+ffffffff813893b7:      4c 89 b5 70 ff ff ff    mov    %r14,-0x90(%rbp)

And removing the TYPE_ATTRIBUTES() poking makes the register storage
differences go away, but there's still a 0x40 byte offset delta.

I'll continue looking at this tomorrow.


Kees Cook
Pixel Security

Powered by blists - more mailing lists

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.