Re: Modify cr0 at dom0

[machi1271 <machi1271@gmail.com>]

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I'v tried the way to modify CR0 by writing to it directly. But I got the following error:
\x02(XEN) traps.c:1768:d0 Attempt to change unmodifiable CR0 flags.
general protection fault: 0000 [1] SMP 
last sysfs file: /devices/pci0000:00/0000:00:00.0/resource
CPU 0 
Modules linked in: fsp(U) autofs4 hidp rfcomm l2cap bluetooth lockd sunrpc ip_conntrack_netbios_ns ip_conntrack nfnetlink xt_tcpudp iptable_filter ip_tables x_tables acpiphp loop dm_multipath scsi_dh video backlight sbs power_meter hwmon i2c_ec dell_wmi wmi button battery asus_acpi ac ipv6 xfrm_nalgo crypto_api lp joydev floppy sg snd_ens1371 gameport i2c_piix4 snd_rawmidi snd_ac97_codec ac97_bus snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq i2c_core pcspkr snd_seq_device snd_pcm_oss snd_mixer_oss snd_pcm e1000 snd_timer snd soundcore snd_page_alloc shpchp serio_raw ide_cd parport_pc parport cdrom serial_core dm_raid45 dm_message dm_region_hash dm_mem_cache dm_snapshot dm_zero dm_mirror dm_log dm_mod ata_piix libata mptspi mptscsih mptbase scsi_transport_spi sd_mod scsi_mod ext3 jbd uhci_hcd ohci_hcd ehci_hcd
Pid: 4103, comm: insmod Tainted: G      2.6.18-194.el5xen #1
RIP: e030:[<ffffffff88218020>]  [<ffffffff88218020>] :fsp:init_fsp+0x20/0x2d
RSP: e02b:ffff880025145f50  EFLAGS: 00010202
RAX: 000000008004003b RBX: ffffffff88680600 RCX: 0000000000000000
RDX: 000000008005003b RSI: 0000000000000000 RDI: 0000000000000000
RBP: 000000001fc65060 R08: 000000001fc65060 R09: 0000000000000000
R10: ffff880024967360 R11: ffff880032c42100 R12: 0000000000094ee5
R13: 00002b3383dc6010 R14: 0000000000100000 R15: 0000000000100000
FS:  00002b3383dc5750(0000) GS:ffffffff805d2000(0000) knlGS:0000000000000000
CS:  e033 DS: 0000 ES: 0000
Process insmod (pid: 4103, threadinfo ffff880025144000, task ffff880032c42100)
Stack:  ffffffff802a28e8  0000000000100000  00002b3383dc6010  0000000000000003 
 00007fff5237dbdc  0000000000094ee5  ffffffff802602f9  0000000000000206 
 0000000000000000  0000000000001007 
Call Trace:
 [<ffffffff802a28e8>] sys_init_module+0xaf/0x1f2
 [<ffffffff802602f9>] tracesys+0xab/0xb6


Code: 0f 22 c0 31 c0 48 89 15 3c 09 47 00 c3 00 00 00 00 00 00 00 
RIP  [<ffffffff88218020>] :fsp:init_fsp+0x20/0x2d
 RSP <ffff880025145f50>
 <0>Kernel panic - not syncing: Fatal exception
 (XEN) Domain 0 crashed: rebooting machine in 5 seconds.

Directly modifying CR0 by assembly language seems to modify the real physical register on the  real CPU, 
but I just want to modify dom's virtual CR0 in the vcpu structure, since I want to modify some memory area 
in dom0's kernel which is protected by dom0's vcpu's CR0.WP bit.

Regards~




machi1271

From: Razvan Cojocaru
Date: 2014-10-17 14:48
To: machi1271; xen-devel
Subject: Re: [Xen-devel] Modify cr0 at dom0
On 10/17/14 09:34, machi1271 wrote:
> Thanks Razvan~
>  
> I'm new to Xen and Linux.
> Could you please tell me is there any Xen-independent manner to modify
> CR0, or the memory area protected by CR0.WP bit?

Sure, there's an example here:

https://stackoverflow.com/questions/3962950/how-to-set-control-register-0-cr0-bits-in-x86-64-using-gcc-assembly-on-linux


Razvan

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