Date: Tue, 26 Jun 2018 11:20:12 +0200 From: Solar Designer <solar@...nwall.com> To: owl-dev@...ts.openwall.com Cc: Vasily Averin <vvs@...tuozzo.com> 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: https://openvz.org/Download/kernel/rhel5/028stab122.4 IIRC, this interdiff output is a little over 300 KB. Thank you for your help! Alexander
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