Introduction

In recent HITB XCTF, this technique is used in one heap challenge. I think it’s necessary to give a basic introduction on this also as an extension on my tutorial on largebin in ptmalloc.
The criteria for this exploitation technique is strict compared to other techniques and requires a lot of manual craft to assure the exploit is successful. The advantage of this technique is that the whole exploitation no longer depends on the knowledge of the base address of libc. But the advantage is limited as we still need a known address in advance, which can by repeatedly and reliably modified. Maybe the CTF community may find more potential of such technique in future.
The original information about this technique can be found in [1]. My post is based on this blog.
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Introduction

In this post, I will talk about the seccomp and ptrace step by step. The manual reference of ptrace [6] is heavily recommended for this topic. The whole post will be divided into 6 sections: (1) Introduction of syscall. (2) Introduction of seccomp. (3) Introduction of ptrace. (4) Advanced ptrace. (5) Seccomp Filter and seccomp-tool. and (6) Seccomp escape with ptrace.
I will give many sample codes in the post since I am a newbie in seccomp escape.
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Introduction

In my post on allocation internal on ptmalloc, I actually miss one part of code in _int_malloc . In recent 0CTF 2018, this part of code is used to launch the exploit. Therefore, I decide to introduce this part of code in this post. In my previous posts, I only introduce how large chunks are retrieved from largebin, but I miss the part on how the freed chunks are inserted into largebin. This post will give a detailed introduction on this part.
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Introduction

In this post, I will give an introduction of the PCI device emulation in QEMU. I will start from the function pci_register_bar. Then I will introduce the PCI bus initialization and update. Based on the information given above, I will explain how RTL8139 and MMIO are expected to work through DMA (Direct Memory Access).
I also strongly recommend reading the reference [1] and [2]. They give some other useful information for PCI device in QEMU.
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Introduction

In this post, I will introduce two significant data structures in QEMU: MemoryRegion and AddressSpace. Based on the information given above, I will give more details on the memory initialization in QEMU and address_space_rw, which is the core function of QEMU from my perspective. Furthermore, I give examples to explain what is STDIO and MMIO (memory-mapped IO).
Before reading this post, I strongly recommend reading /qemu/docs/memory.txt first. It will give a basic view of what I will talk about in this post.
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Introduction

In my previous post, I give a basic introduction on pcnet emulation and display the stacktrace of execution flow of the emulation.
In this post I will give a introduction on RTL8139 emulation in QEMU. Different from the previous post, I will omit the execution flow of RTL8139 I/O operation. Instead, I want to put more focus on how the emulated registers are used and how user controlled data go into the vulnerable function and trigger the vulnerability.
In QEMU, all RTL8139 emulation is implemented in rtl8139.c.
The concept of DMA will be introduced in this post. But more details on that will be given in next post.
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Introduction

This post will give a basic introduction on how QEMU emulates a pcnet network card from the view of source code. In QEMU, pcnet-pci.c and pcnet.c are the most important two files that are related with pcnet network card emulation. From my point of view, pcnet-pci.c is for emulating the operation between the QEMU and pcnet device, including device initialization and device IO communication; pcnet.c is for emulating the operation between QEMU and the guest machine, including packet transmission and data processing.
This post post will pick part of the source code of QEMU for explaining the internal of QEMU.
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Introduction

In my previous blog, I mention that MADV_DONTFORK is set to the virtual memory region, which is used as the physical memory of guest machine. In another word, the memory set to MADV_DONTFORK will not be passed to the forked process. In this post, I will prove this hypothesis by undoing the MADV_DONTFORK flag of the memory region and display the flag.

In the exploit given in [1] and [2], the author first changes the protection flag of the PHY_MEM to RWX and prepares the shellcode in PHY_MEM to undo the MADV_DONTFORK flag of PHY_MEM. From my perspective, such a method is tedious for the purpose of this post. Alternatively, I choose to prove the hypothesis via code reuse attack directly.
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