[BitVisor-devel-en:69] Re: How can I convert a gva to gpa?

[hikkikuma1991]

Dear Eiraku san,

Thank you very much.  I can convert a gva to hpa now, and I can dump the memory region of a process' or kernel's gva address. My source code is very similar with the core/debug.c just added a function to read cr3~efer registers.

void 
get_control_regs(ulong * cr0, ulong * cr3, ulong * cr4, u64 * efer){
current->vmctl.read_control_reg (CONTROL_REG_CR0, cr0);
current->vmctl.read_control_reg (CONTROL_REG_CR3, cr3);
current->vmctl.read_control_reg (CONTROL_REG_CR4, cr4);
current->vmctl.read_msr (MSR_IA32_EFER, efer);
}

But there is a little trick, that is the value of cr3 is the vcpu's current state, which means if u are running a process A, and A has invoked get_control_regs() to get cr3, then the cr3's value is process A's page directory's gpa address. If u want to convert process B's gva, it should not work.

And I have another question, is there anyone can answer me? How to pause bitvisor and resume it? I need to pause vm for consistent memory access although it seems work good if I don't pause vm. But I still need some help or knowledge of pausing and resuming the bitvisor.

Augustus Liu <hikkikuma1991 at 163.com>




发件人：bitvisor-devel-en-request at bitvisor.org
发送时间：2015-12-09 11:00
主题：BitVisor-devel-en Digest, Vol 26, Issue 2
收件人："bitvisor-devel-en"<bitvisor-devel-en at bitvisor.org>
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Today's Topics: 

   1. [BitVisor-devel-en:66] Re: How can I convert a gva to gpa? 
      (Hideki EIRAKU) 


---------------------------------------------------------------------- 

Message: 1 
Date: Tue, 08 Dec 2015 15:39:09 +0900 (JST) 
From: Hideki EIRAKU <hdk at igel.co.jp> 
To: bitvisor-devel-en at bitvisor.org 
Subject: [BitVisor-devel-en:66] Re: How can I convert a gva to gpa? 
Message-ID: <20151208.153909.26311979.hdk at igel.co.jp> 
Content-Type: Text/Plain; charset=us-ascii 

Hello, 

From: "hikkikuma1991"<hikkikuma1991 at 163.com> 
Subject: [BitVisor-devel-en:65] How can I convert a gva to gpa? 
Date: Mon, 7 Dec 2015 15:02:34 +0800 

> But I met a problem when I  tried to convert guest virtual address to guest physics address. I copied the void memdump_gvirt(u64 gvirt) fuction in "process/debug.c", but it always returned a VMMERR_PAGE_NOT_PRESENT value to me, so I want to know is this func really works, or how could I use the func to convert a gva? And if it doesn't work, would you mind giving me some advices to finish this func? By the way, my enviroment is bitvisor 1.3 with 64bit Ubuntu 12.04. 

The memdump_gvirt() function in core/debug.c uses the 
cpu_mmu_get_pte() function to convert virtual address to physical 
address.  The cpu_mmu_get_pte() function requires register values of 
cr0, cr3, cr4, and, efer.  Those registers contain information about 
page tables.  The cpu_mmu_get_pte() function should work properly 
because it is used by instruction interpretation for real-address mode 
emulation for old processors like Intel Core 2 Duo. 

To convert address of current running process or kernel in the guest 
operating system, use current->vmctl.read_control_reg() and 
current->vmctl.read_msr() function to get those registers, then use 
the cpu_mmu_get_pte() function.  Functions such as read_linearaddr_b() 
in core/cpu_mmu.c use this way. 

VMMERR_PAGE_NOT_PRESENT means the page is not present.  For example, 
if the virtual address is zero, usually the page is not present 
because it is NULL pointer address.  For another example, a page that 
a process allocated may not be present because of deferred page 
allocation or swapping. 

--  
Hideki EIRAKU <hdk at igel.co.jp> 


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