Well, first of all, i did a wrong copy and paste when i mapped the
code, the mask i apply is 0xFFFFE000.
I checked the control registers, cr0 and cr3 to ensure that paging is
used, i just have to understand now how it is implemented.
Digging right now in several file, prom mm.c to page.h, paging.h to
understand how i can walk through the memory.
Any hint or pointer to documentation would be helpful
Thanks
Fred
Le Mon, 16 Feb 2009 17:58:24 +0100,
Frederic Beck <frederic.beck@xxxxxxxx> a écrit :
> Hello
>
> I managed to do what i wanted with my module (finally gave up on the
> syscall and did everything in the module init), and i foudn the
> offsets i was looking for. I later found out that what i've done was
> already available via XenAccess (tools/linux-offset-finder).
>
> I have the following offsets:
> linux_name = 0x225;
> linux_tasks = 0xd0;
> linux_mm = 0xe8;
> linux_pid = 0x10c;
> linux_pgd = 0x24;
> linux_addr = 0x84;
>
> After disabling fast system calls handling, i modified do_guest_trap
> in xen/arch/x86/traps.c. I get the user regs to have access to the CPU
> registers EAX, EIP and ESP (info i wanna log via the tracing). I take
> the ESP and apply the mask 0xFFFFF000 to get the base address of the
> thread_info struct.
>
> user_regs = guest_cpu_user_regs();
> base_addr = (user_regs->esp & 0xFFFFF000);
>
> Then the first 4 bytes after this base_addr are on a regular system a
> pointer to a task_struct where the PId of the current task is stored,
> which i wanna get. On a regular OS (i tested on Dom0 or DomU) I can
> find easily the PID and print it out. I would like to do the same in
> the hypervisor.
>
> I tried to map the same code without modification, but i begin reading
> memory addresses that do not exist and the hypervisor crashes when i
> create my DomU. So far, i'm not very surprised, as there must be some
> virtual memory handling that i'm missing.
>
> However, i do not understand well how i can do the mapping. how do i
> map this kernel address in the hypervisor to read the right memory
> address ?
>
> I guess that this mapping will be different for HVM and PV domains ?
> Is there a function that dynamically detects what kind of domain the
> guest is ?
>
> Moreover, i found out in XenAccess that the right formula to get the
> PID would be
> memcpy(&pid, memory + offset + PID_OFFSET - TASKS_OFFSET,4);
> I guess that memory is the base adress of the virtual stack. How can i
> find that value ? in that case the base_addr i calculated earlier
> would be the offset ?
>
> Thanks for the help!
>
> Regards
> Fred
>
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