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Date: Tue, 26 Jun 2018 11:20:12 +0200
From: Solar Designer <>
Cc: Vasily Averin <>
Subject: Re: 32-bit syscall breakage in -431 kernel with KAISER

On Mon, Jun 25, 2018 at 10:48:28PM +0200, Pavel Kankovsky wrote:
> To get more information, I added show_regs(task_pt_regs(current)) to the 
> beginning of dev_ifconf() and here is the result:
> CPU 0, VCPU 0:0
> Modules linked in: vzethdev simfs exportfs vzdquota vznetdev vzmon vzdev
> Pid: 986, comm: ifconfig32 Tainted:  P     --------------------    
> 2.6.18-431.el5.028stab123.1.owl1xxx #1 028stab123
> RIP: 0292:[<0000000000000073>]  [<0000000000000073>]
> RSP: 007b:000000000000007b  EFLAGS: bf98675c
> RAX: 0000000000008912 RBX: 0000000000000000 RCX: 00000000bf986774
> RDX: 0000000000000004 RSI: 00000000bf986774 RDI: 0000000000000036
> RBP: ffffffff80065a3e R08: 0000000000000036 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> FS:  0000000000000000(0000) GS:ffffffff805b2000(0033) knlGS:00000000b7e44a90
> CS:  0060 DS: 007b ES: 007b CR0: 000000008005003b
> CR2: 00000000b7eab100 CR3: 000000003f808000 CR4: 00000000000006e0
> Userland rsp seems to be 0x7b and this makes compat_alloc_user_space() 
> fail.
> It seems to me the data are shifted: the value reported as "EFLAGS" looks 
> like an actual userland stack pointer, "0000000000000073" should probably 
> be CS rather than RIP (the offset) etc.

Yes.  Shifting is what I had expected - I was looking for extra pushes
not undone with pops, or similar, before calling the syscall function,
but didn't immediately see that kind of change in there.  Maybe I
overlooked or maybe it's not exactly the pattern to look for; I'm not
familiar with how/where the pt_regs pointer is derived.  Maybe you'd
take a look?

You can interdiff our current patch-431* vs. the one that worked fine
before, from here:

IIRC, this interdiff output is a little over 300 KB.

Thank you for your help!


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