From: Andrew Lutomirski <amluto@gmail.com>
To: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>, comex <comexk@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Alexander van Heukelum <heukelum@fastmail.fm>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Borislav Petkov <bp@alien8.de>,
Arjan van de Ven <arjan.van.de.ven@intel.com>,
Brian Gerst <brgerst@gmail.com>,
Alexandre Julliard <julliard@winehq.com>,
Andi Kleen <andi@firstfloor.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*
Date: Mon, 28 Apr 2014 17:20:51 -0700 [thread overview]
Message-ID: <CAObL_7FZRji6ivcVvTQ4r=KULCA760fr_wKqkjaYKGL=KLOQRA@mail.gmail.com> (raw)
In-Reply-To: <CAObL_7HVOjpgp0=Ot9ih2tb6x7xv6MGstu-Krad+rrO4cVqyTg@mail.gmail.com>
On Mon, Apr 28, 2014 at 5:02 PM, Andrew Lutomirski <amluto@gmail.com> wrote:
> On Mon, Apr 28, 2014 at 4:08 PM, H. Peter Anvin <hpa@linux.intel.com> wrote:
>> On 04/28/2014 04:05 PM, H. Peter Anvin wrote:
>>>
>>> So I tried writing this bit up, but it fails in some rather spectacular
>>> ways. Furthermore, I have been unable to debug it under Qemu, because
>>> breakpoints don't work right (common Qemu problem, sadly.)
>>>
>>> The kernel code is at:
>>>
>>> https://git.kernel.org/cgit/linux/kernel/git/hpa/espfix64.git/
>>>
>>> There are two tests:
>>>
>>> git://git.zytor.com/users/hpa/test16/test16.git, build it, and run
>>> ./run16 test/hello.elf
>>> http://www.zytor.com/~hpa/ldttest.c
>>>
>>> The former will exercise the irq_return_ldt path, but not the fault
>>> path; the latter will exercise the fault path, but doesn't actually use
>>> a 16-bit segment.
>>>
>>> Under the 3.14 stock kernel, the former should die with SIGBUS and the
>>> latter should pass.
>>>
>>
>> Current status of the above code: if I remove the randomization in
>> espfix_64.c then the first test passes; the second generally crashes the
>> machine. With the randomization there, both generally crash the machine.
>>
>> All my testing so far has been under KVM or Qemu, so there is always the
>> possibility that I'm chasing a KVM/Qemu bug, but I suspect it is
>> something simpler than that.
>
> I'm compiling your branch. In the mean time, two possibly stupid questions:
>
> What's the assembly code in the double-fault entry for?
>
> Have you tried hbreak in qemu? I've had better luck with hbreak than
> regular break in the past.
>
ldttest segfaults on 3.13 and 3.14 for me. It reboots (triple fault?)
on your branch. It even said this:
qemu-system-x86_64: 9pfs:virtfs_reset: One or more uncluncked fids
found during reset
I have no idea what an uncluncked fd is :)
hello.elf fails to sigbus. weird. gdb says:
1: x/i $pc
=> 0xffffffff8170559c <irq_return_ldt+90>:
jmp 0xffffffff81705537 <irq_return_iret>
(gdb) si
<signal handler called>
1: x/i $pc
=> 0xffffffff81705537 <irq_return_iret>: iretq
(gdb) si
Cannot access memory at address 0xf0000000f
(gdb) info registers
rax 0xffe4000f00001000 -7881234923384832
rbx 0x1000000010 68719476752
rcx 0xffe4f5580000f000 -7611541041909760
rdx 0x805d000 134598656
rsi 0x102170000ffe3 283772784279523
rdi 0xf00000007 64424509447
rbp 0xf0000000f 0xf0000000f
rsp 0xf0000000f 0xf0000000f
r8 0x0 0
r9 0x0 0
r10 0x0 0
r11 0x0 0
r12 0x0 0
r13 0x0 0
r14 0x0 0
r15 0x0 0
rip 0x0 0x0 <irq_stack_union>
eflags 0x0 [ ]
cs 0x0 0
ss 0x37f 895
ds 0x0 0
es 0x0 0
fs 0x0 0
---Type <return> to continue, or q <return> to quit---
gs 0x0 0
I got this with 'hbreak irq_return_ldt' using 'target remote :1234'
and virtme-run --console --kimg
~/apps/linux-devel/arch/x86/boot/bzImage --qemu-opts -s
This set of registers looks thoroughly bogus. I don't trust it. I'm
now stuck -- single-stepping stays exactly where it started.
Something is rather screwed up here. Telling gdb to continue causes
gdb to explode and 'Hello, Afterworld!' to be displayed.
I was not able to get a breakpoint on __do_double_fault to hit.
FWIW, I think that gdb is known to have issues debugging a guest that
switches bitness.
--Andy
next prev parent reply other threads:[~2014-04-29 0:21 UTC|newest]
Thread overview: 136+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-11 17:36 [tip:x86/urgent] x86-64, modify_ldt: Ban 16-bit segments on 64-bit kernels tip-bot for H. Peter Anvin
2014-04-11 18:12 ` Andy Lutomirski
2014-04-11 18:20 ` H. Peter Anvin
2014-04-11 18:27 ` Brian Gerst
2014-04-11 18:29 ` H. Peter Anvin
2014-04-11 18:35 ` Brian Gerst
2014-04-11 21:16 ` Andy Lutomirski
2014-04-11 21:24 ` H. Peter Anvin
2014-04-11 21:53 ` Andy Lutomirski
2014-04-11 21:59 ` H. Peter Anvin
2014-04-11 22:15 ` Andy Lutomirski
2014-04-11 22:18 ` H. Peter Anvin
2014-04-13 4:20 ` H. Peter Anvin
2014-04-12 23:26 ` Alexander van Heukelum
2014-04-12 23:31 ` H. Peter Anvin
2014-04-12 23:49 ` Alexander van Heukelum
2014-04-13 0:03 ` H. Peter Anvin
2014-04-13 1:25 ` Andy Lutomirski
2014-04-13 1:29 ` Andy Lutomirski
2014-04-13 3:00 ` H. Peter Anvin
2014-04-11 21:34 ` Linus Torvalds
2014-04-11 18:41 ` Linus Torvalds
2014-04-11 18:45 ` Brian Gerst
2014-04-11 18:50 ` Linus Torvalds
2014-04-12 4:44 ` Brian Gerst
2014-04-12 17:18 ` H. Peter Anvin
2014-04-12 19:35 ` Borislav Petkov
2014-04-12 19:44 ` H. Peter Anvin
2014-04-12 20:11 ` Borislav Petkov
2014-04-12 20:34 ` Brian Gerst
2014-04-12 20:59 ` Borislav Petkov
2014-04-12 21:13 ` Brian Gerst
2014-04-12 21:40 ` Borislav Petkov
2014-04-14 7:21 ` Ingo Molnar
2014-04-14 9:44 ` Borislav Petkov
2014-04-14 9:47 ` Ingo Molnar
2014-04-12 21:53 ` Linus Torvalds
2014-04-12 22:25 ` H. Peter Anvin
2014-04-13 2:56 ` Andi Kleen
2014-04-13 3:02 ` H. Peter Anvin
2014-04-13 3:13 ` Linus Torvalds
2014-04-12 20:29 ` Brian Gerst
2014-04-14 7:48 ` Alexandre Julliard
2014-05-07 9:18 ` Sven Joachim
2014-05-07 10:18 ` Borislav Petkov
2014-05-07 16:57 ` Linus Torvalds
2014-05-07 17:09 ` H. Peter Anvin
2014-05-07 17:50 ` Alexandre Julliard
2014-05-08 6:43 ` Sven Joachim
2014-05-08 13:50 ` H. Peter Anvin
2014-05-08 20:13 ` H. Peter Anvin
2014-05-08 20:40 ` H. Peter Anvin
2014-05-12 13:16 ` Josh Boyer
2014-05-12 16:52 ` H. Peter Anvin
2014-05-14 23:43 ` [tip:x86/urgent] x86-64, modify_ldt: Make support for 16-bit segments a runtime option tip-bot for Linus Torvalds
2014-04-11 18:46 ` [tip:x86/urgent] x86-64, modify_ldt: Ban 16-bit segments on 64-bit kernels H. Peter Anvin
2014-04-14 7:27 ` Ingo Molnar
2014-04-14 15:45 ` H. Peter Anvin
2014-04-13 2:54 ` Andi Kleen
2014-04-21 22:47 ` [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE* H. Peter Anvin
2014-04-21 23:19 ` Andrew Lutomirski
2014-04-21 23:29 ` H. Peter Anvin
2014-04-22 0:37 ` Andrew Lutomirski
2014-04-22 0:53 ` H. Peter Anvin
2014-04-22 1:06 ` Andrew Lutomirski
2014-04-22 1:14 ` H. Peter Anvin
2014-04-22 1:28 ` Andrew Lutomirski
2014-04-22 1:47 ` H. Peter Anvin
2014-04-22 1:53 ` Andrew Lutomirski
2014-04-22 11:23 ` Borislav Petkov
2014-04-22 14:46 ` Borislav Petkov
2014-04-22 16:03 ` Andrew Lutomirski
2014-04-22 16:10 ` H. Peter Anvin
2014-04-22 16:33 ` Andrew Lutomirski
2014-04-22 16:43 ` Linus Torvalds
2014-04-22 17:00 ` Andrew Lutomirski
2014-04-22 17:04 ` Linus Torvalds
2014-04-22 17:11 ` Andrew Lutomirski
2014-04-22 17:15 ` H. Peter Anvin
2014-04-23 9:54 ` One Thousand Gnomes
2014-04-23 15:53 ` H. Peter Anvin
2014-04-23 17:08 ` Andrew Lutomirski
2014-04-23 17:16 ` H. Peter Anvin
2014-04-23 17:25 ` Andrew Lutomirski
2014-04-23 17:28 ` H. Peter Anvin
2014-04-23 17:45 ` Andrew Lutomirski
2014-04-22 17:19 ` Linus Torvalds
2014-04-22 17:29 ` H. Peter Anvin
2014-04-22 17:46 ` Andrew Lutomirski
2014-04-22 17:59 ` H. Peter Anvin
2014-04-22 18:03 ` Brian Gerst
2014-04-22 18:06 ` H. Peter Anvin
2014-04-22 18:17 ` Brian Gerst
2014-04-22 18:51 ` H. Peter Anvin
2014-04-22 19:55 ` Brian Gerst
2014-04-22 20:17 ` H. Peter Anvin
2014-04-22 23:08 ` Brian Gerst
2014-04-22 23:39 ` Andi Kleen
2014-04-22 23:40 ` H. Peter Anvin
2014-04-22 17:11 ` H. Peter Anvin
2014-04-22 17:26 ` Borislav Petkov
2014-04-22 17:29 ` Andrew Lutomirski
2014-04-22 19:27 ` Borislav Petkov
2014-04-23 6:24 ` H. Peter Anvin
2014-04-23 8:57 ` Alexandre Julliard
2014-04-22 17:09 ` H. Peter Anvin
2014-04-22 17:20 ` Andrew Lutomirski
2014-04-22 17:24 ` H. Peter Anvin
2014-04-22 11:25 ` Borislav Petkov
2014-04-23 1:17 ` H. Peter Anvin
2014-04-23 1:23 ` Andrew Lutomirski
2014-04-23 1:42 ` H. Peter Anvin
2014-04-23 14:24 ` Boris Ostrovsky
2014-04-23 16:56 ` H. Peter Anvin
2014-04-28 13:04 ` Konrad Rzeszutek Wilk
2014-04-25 21:02 ` Konrad Rzeszutek Wilk
2014-04-25 21:16 ` H. Peter Anvin
2014-04-24 4:13 ` comex
2014-04-24 4:53 ` Andrew Lutomirski
2014-04-24 22:24 ` H. Peter Anvin
2014-04-24 22:31 ` Andrew Lutomirski
2014-04-24 22:37 ` H. Peter Anvin
2014-04-24 22:43 ` Andrew Lutomirski
2014-04-28 23:05 ` H. Peter Anvin
2014-04-28 23:08 ` H. Peter Anvin
2014-04-29 0:02 ` Andrew Lutomirski
2014-04-29 0:15 ` H. Peter Anvin
2014-04-29 0:20 ` Andrew Lutomirski [this message]
2014-04-29 2:38 ` H. Peter Anvin
2014-04-29 2:44 ` H. Peter Anvin
2014-04-29 3:45 ` H. Peter Anvin
2014-04-29 3:47 ` H. Peter Anvin
2014-04-29 4:36 ` H. Peter Anvin
2014-04-29 7:14 ` H. Peter Anvin
2014-04-25 12:02 ` Pavel Machek
2014-04-25 21:20 ` H. Peter Anvin
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