Re: KMSAN: kernel-infoleak in kvm_vcpu_write_guest_page

From: Alexander Potapenko
Date: Wed Nov 07 2018 - 07:10:20 EST

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On Wed, Nov 7, 2018 at 2:38 AM syzbot
<syzbot+ded1696f6b50b615b630@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 88b95ef4c780 kmsan: use MSan assembly instrumentation
> git tree: https://github.com/google/kmsan.git/master
> console output: https://syzkaller.appspot.com/x/log.txt?x=12505e33400000
> kernel config: https://syzkaller.appspot.com/x/.config?x=8df5fc509a1b351b
> dashboard link: https://syzkaller.appspot.com/bug?extid=ded1696f6b50b615b630
> compiler: clang version 8.0.0 (trunk 343298)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15ce62f5400000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=174efca3400000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+ded1696f6b50b615b630@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ==================================================================
> BUG: KMSAN: kernel-infoleak in __copy_to_user include/linux/uaccess.h:121
> [inline]
> BUG: KMSAN: kernel-infoleak in __kvm_write_guest_page
> arch/x86/kvm/../../../virt/kvm/kvm_main.c:1849 [inline]
> BUG: KMSAN: kernel-infoleak in kvm_vcpu_write_guest_page+0x39a/0x510
> arch/x86/kvm/../../../virt/kvm/kvm_main.c:1870
> CPU: 0 PID: 7918 Comm: syz-executor542 Not tainted 4.19.0+ #77
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x32d/0x480 lib/dump_stack.c:113
> kmsan_report+0x1a2/0x2e0 mm/kmsan/kmsan.c:911
> kmsan_internal_check_memory+0x34c/0x430 mm/kmsan/kmsan.c:991
> kmsan_copy_to_user+0x85/0xe0 mm/kmsan/kmsan_hooks.c:552
> __copy_to_user include/linux/uaccess.h:121 [inline]
> __kvm_write_guest_page arch/x86/kvm/../../../virt/kvm/kvm_main.c:1849
> [inline]
> kvm_vcpu_write_guest_page+0x39a/0x510
> arch/x86/kvm/../../../virt/kvm/kvm_main.c:1870
> nested_release_vmcs12 arch/x86/kvm/vmx.c:8441 [inline]
> handle_vmptrld+0x2384/0x26b0 arch/x86/kvm/vmx.c:8907
> vmx_handle_exit+0x1e81/0xbac0 arch/x86/kvm/vmx.c:10128
> vcpu_enter_guest arch/x86/kvm/x86.c:7667 [inline]
> vcpu_run arch/x86/kvm/x86.c:7730 [inline]
> kvm_arch_vcpu_ioctl_run+0xac32/0x11d80 arch/x86/kvm/x86.c:7930
> kvm_vcpu_ioctl+0xfb1/0x1f90 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2590
> do_vfs_ioctl+0xf77/0x2d30 fs/ioctl.c:46
> ksys_ioctl fs/ioctl.c:702 [inline]
> __do_sys_ioctl fs/ioctl.c:709 [inline]
> __se_sys_ioctl+0x1da/0x270 fs/ioctl.c:707
> __x64_sys_ioctl+0x4a/0x70 fs/ioctl.c:707
> do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
> entry_SYSCALL_64_after_hwframe+0x63/0xe7
> RIP: 0033:0x44b6e9
> Code: e8 dc e6 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7
> 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
> ff 0f 83 2b ff fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f096b292ce8 EFLAGS: 00000206 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00000000006e3c48 RCX: 000000000044b6e9
> RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000005
> RBP: 00000000006e3c40 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000206 R12: 00000000006e3c4c
> R13: 00007ffd978aeb2f R14: 00007f096b2939c0 R15: 00000000006e3d4c
>
> Uninit was created at:
> kmsan_save_stack_with_flags mm/kmsan/kmsan.c:252 [inline]
> kmsan_internal_poison_shadow+0xc8/0x1e0 mm/kmsan/kmsan.c:177
> kmsan_kmalloc+0x98/0x110 mm/kmsan/kmsan_hooks.c:104
> __kmalloc+0x14c/0x4d0 mm/slub.c:3789
> kmalloc include/linux/slab.h:518 [inline]
> enter_vmx_operation+0x980/0x1a90 arch/x86/kvm/vmx.c:8278
> vmx_set_nested_state+0xc3a/0x1530 arch/x86/kvm/vmx.c:14045
> kvm_arch_vcpu_ioctl+0x4fc9/0x73a0 arch/x86/kvm/x86.c:4057
> kvm_vcpu_ioctl+0xca3/0x1f90 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2742
> do_vfs_ioctl+0xf77/0x2d30 fs/ioctl.c:46
> ksys_ioctl fs/ioctl.c:702 [inline]
> __do_sys_ioctl fs/ioctl.c:709 [inline]
> __se_sys_ioctl+0x1da/0x270 fs/ioctl.c:707
> __x64_sys_ioctl+0x4a/0x70 fs/ioctl.c:707
> do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
> entry_SYSCALL_64_after_hwframe+0x63/0xe7
>
> Bytes 1000-4095 of 4096 are uninitialized
> Memory access of size 4096 starts at ffff8801b5157000
> ==================================================================
This appears to be a real bug in KVM.
Please see a simplified reproducer attached.

>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>
> --
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--
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-StraÃe, 33
80636 MÃnchen

GeschÃftsfÃhrer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
// autogenerated by syzkaller (https://github.com/google/syzkaller)

#define _GNU_SOURCE

#include <dirent.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <setjmp.h>
#include <signal.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mount.h>
#include <sys/prctl.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

#include <linux/futex.h>
#include <linux/kvm.h>

const char kvm_asm64_init_vm[] =
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"\x0f\x79\xd0\x48\xc7\xc2\x10\x28\x00\x00\x48\xc7\xc0\x00\x00\x00\x00\x0f"
"\x79\xd0\x0f\x20\xc0\x48\xc7\xc2\x00\x68\x00\x00\x48\x89\xc0\x0f\x79\xd0"
"\x0f\x20\xd8\x48\xc7\xc2\x02\x68\x00\x00\x48\x89\xc0\x0f\x79\xd0\x0f\x20"
"\xe0\x48\xc7\xc2\x04\x68\x00\x00\x48\x89\xc0\x0f\x79\xd0\x48\xc7\xc0\x18"
"\x5f\x00\x00\x48\x8b\x10\x48\xc7\xc0\x20\x5f\x00\x00\x48\x8b\x08\x48\x31"
"\xc0\x0f\x78\xd0\x48\x31\xc8\x0f\x79\xd0\x0f\x01\xc2\x48\xc7\xc2\x00\x44"
"\x00\x00\x0f\x78\xd0\xf4";
const char kvm_asm64_vm_exit[] = "\x48\xc7\xc3\x00\x44\x00\x00\x0f\x78\xda\x48"
"\xc7\xc3\x02\x44\x00\x00\x0f\x78\xd9\x48\xc7"
"\xc0\x00\x64\x00\x00\x0f\x78\xc0\x48\xc7\xc3"
"\x1e\x68\x00\x00\x0f\x78\xdb\xf4";

#define ADDR_TEXT 0x0000
#define ADDR_GDT 0x1000
#define ADDR_LDT 0x1800
#define ADDR_PML4 0x2000
#define ADDR_PDP 0x3000
#define ADDR_PD 0x4000
#define ADDR_STACK0 0x0f80
#define ADDR_VAR_HLT 0x2800
#define ADDR_VAR_SYSRET 0x2808
#define ADDR_VAR_SYSEXIT 0x2810
#define ADDR_VAR_IDT 0x3800
#define ADDR_VAR_TSS64 0x3a00
#define ADDR_VAR_TSS64_CPL3 0x3c00
#define ADDR_VAR_TSS16 0x3d00
#define ADDR_VAR_TSS16_2 0x3e00
#define ADDR_VAR_TSS16_CPL3 0x3f00
#define ADDR_VAR_TSS32 0x4800
#define ADDR_VAR_TSS32_2 0x4a00
#define ADDR_VAR_TSS32_CPL3 0x4c00
#define ADDR_VAR_TSS32_VM86 0x4e00
#define ADDR_VAR_VMXON_PTR 0x5f00
#define ADDR_VAR_VMCS_PTR 0x5f08
#define ADDR_VAR_VMEXIT_PTR 0x5f10
#define ADDR_VAR_VMWRITE_FLD 0x5f18
#define ADDR_VAR_VMWRITE_VAL 0x5f20
#define ADDR_VAR_VMXON 0x6000
#define ADDR_VAR_VMCS 0x7000
#define ADDR_VAR_VMEXIT_CODE 0x9000
#define ADDR_VAR_USER_CODE 0x9100
#define ADDR_VAR_USER_CODE2 0x9120

#define SEL_LDT (1 << 3)
#define SEL_CS16 (2 << 3)
#define SEL_DS16 (3 << 3)
#define SEL_CS16_CPL3 ((4 << 3) + 3)
#define SEL_DS16_CPL3 ((5 << 3) + 3)
#define SEL_CS32 (6 << 3)
#define SEL_DS32 (7 << 3)
#define SEL_CS32_CPL3 ((8 << 3) + 3)
#define SEL_DS32_CPL3 ((9 << 3) + 3)
#define SEL_CS64 (10 << 3)
#define SEL_DS64 (11 << 3)
#define SEL_CS64_CPL3 ((12 << 3) + 3)
#define SEL_DS64_CPL3 ((13 << 3) + 3)
#define SEL_CGATE16 (14 << 3)
#define SEL_TGATE16 (15 << 3)
#define SEL_CGATE32 (16 << 3)
#define SEL_TGATE32 (17 << 3)
#define SEL_CGATE64 (18 << 3)
#define SEL_CGATE64_HI (19 << 3)
#define SEL_TSS16 (20 << 3)
#define SEL_TSS16_2 (21 << 3)
#define SEL_TSS16_CPL3 ((22 << 3) + 3)
#define SEL_TSS32 (23 << 3)
#define SEL_TSS32_2 (24 << 3)
#define SEL_TSS32_CPL3 ((25 << 3) + 3)
#define SEL_TSS32_VM86 (26 << 3)
#define SEL_TSS64 (27 << 3)
#define SEL_TSS64_HI (28 << 3)
#define SEL_TSS64_CPL3 ((29 << 3) + 3)
#define SEL_TSS64_CPL3_HI (30 << 3)

#define MSR_IA32_SYSENTER_CS 0x174
#define MSR_IA32_SYSENTER_ESP 0x175
#define MSR_IA32_SYSENTER_EIP 0x176
#define MSR_IA32_STAR 0xC0000081
#define MSR_IA32_LSTAR 0xC0000082

#define PREFIX_SIZE 0xba1d

#define CR0_PE 1
#define CR0_MP (1 << 1)
#define CR0_EM (1 << 2)
#define CR0_TS (1 << 3)
#define CR0_ET (1 << 4)
#define CR0_NE (1 << 5)

#define CR4_PAE (1 << 5)

#define EFER_SCE 1
#define EFER_LME (1 << 8)
#define PDE64_PRESENT 1
#define PDE64_RW (1 << 1)
#define PDE64_USER (1 << 2)
#define PDE64_PS (1 << 7)

#define MIN_STRLEN 1
void dump_buf(unsigned char *buf, int len) {
int i, nz = 0;
for (i = 0; i < len; i++) {
if (buf[i]) {
nz = 1;
break;
}
}
if (!nz)
// The buffer is empty.
return;

//pthread_mutex_lock(&out_mutex);
for (i = 0; i < len; i++) {
if (buf[i]) {
int str_len = strlen(&buf[i]);
// Short string pieces are too boring.
if (str_len >= MIN_STRLEN) {
unsigned char *c;
for (c = &buf[i]; c < &buf[i + str_len]; c++) {
if ((*c > 127) || ((*c < 32) && (*c != 10) && (*c != 13))) {
*c = ' ';
continue;
}
}
// Dump the buffer.
fprintf(stderr, "%s\n", &buf[i]);
}
i += str_len;
}
}
//pthread_mutex_unlock(&out_mutex);
}

struct tss16 {
uint16_t prev;
uint16_t sp0;
uint16_t ss0;
uint16_t sp1;
uint16_t ss1;
uint16_t sp2;
uint16_t ss2;
uint16_t ip;
uint16_t flags;
uint16_t ax;
uint16_t cx;
uint16_t dx;
uint16_t bx;
uint16_t sp;
uint16_t bp;
uint16_t si;
uint16_t di;
uint16_t es;
uint16_t cs;
uint16_t ss;
uint16_t ds;
uint16_t ldt;
} __attribute__((packed));

struct tss32 {
uint16_t prev, prevh;
uint32_t sp0;
uint16_t ss0, ss0h;
uint32_t sp1;
uint16_t ss1, ss1h;
uint32_t sp2;
uint16_t ss2, ss2h;
uint32_t cr3;
uint32_t ip;
uint32_t flags;
uint32_t ax;
uint32_t cx;
uint32_t dx;
uint32_t bx;
uint32_t sp;
uint32_t bp;
uint32_t si;
uint32_t di;
uint16_t es, esh;
uint16_t cs, csh;
uint16_t ss, ssh;
uint16_t ds, dsh;
uint16_t fs, fsh;
uint16_t gs, gsh;
uint16_t ldt, ldth;
uint16_t trace;
uint16_t io_bitmap;
} __attribute__((packed));

struct tss64 {
uint32_t reserved0;
uint64_t rsp[3];
uint64_t reserved1;
uint64_t ist[7];
uint64_t reserved2;
uint32_t reserved3;
uint32_t io_bitmap;
} __attribute__((packed));

static void fill_segment_descriptor(uint64_t* dt, uint64_t* lt,
struct kvm_segment* seg)
{
uint16_t index = seg->selector >> 3;
uint64_t limit = seg->g ? seg->limit >> 12 : seg->limit;
uint64_t sd = (limit & 0xffff) | (seg->base & 0xffffff) << 16 |
(uint64_t)seg->type << 40 | (uint64_t)seg->s << 44 |
(uint64_t)seg->dpl << 45 | (uint64_t)seg->present << 47 |
(limit & 0xf0000ULL) << 48 | (uint64_t)seg->avl << 52 |
(uint64_t)seg->l << 53 | (uint64_t)seg->db << 54 |
(uint64_t)seg->g << 55 | (seg->base & 0xff000000ULL) << 56;
dt[index] = sd;
lt[index] = sd;
}

static void fill_segment_descriptor_dword(uint64_t* dt, uint64_t* lt,
struct kvm_segment* seg)
{
fill_segment_descriptor(dt, lt, seg);
uint16_t index = seg->selector >> 3;
dt[index + 1] = 0;
lt[index + 1] = 0;
}

static void setup_syscall_msrs(int cpufd, uint16_t sel_cs, uint16_t sel_cs_cpl3)
{
char buf[sizeof(struct kvm_msrs) + 5 * sizeof(struct kvm_msr_entry)];
memset(buf, 0, sizeof(buf));
struct kvm_msrs* msrs = (struct kvm_msrs*)buf;
struct kvm_msr_entry* entries = msrs->entries;
msrs->nmsrs = 5;
entries[0].index = MSR_IA32_SYSENTER_CS;
entries[0].data = sel_cs;
entries[1].index = MSR_IA32_SYSENTER_ESP;
entries[1].data = ADDR_STACK0;
entries[2].index = MSR_IA32_SYSENTER_EIP;
entries[2].data = ADDR_VAR_SYSEXIT;
entries[3].index = MSR_IA32_STAR;
entries[3].data = ((uint64_t)sel_cs << 32) | ((uint64_t)sel_cs_cpl3 << 48);
entries[4].index = MSR_IA32_LSTAR;
entries[4].data = ADDR_VAR_SYSRET;
ioctl(cpufd, KVM_SET_MSRS, msrs);
}

static void setup_64bit_idt(struct kvm_sregs* sregs, char* host_mem,
uintptr_t guest_mem)
{
sregs->idt.base = guest_mem + ADDR_VAR_IDT;
sregs->idt.limit = 0x1ff;
uint64_t* idt = (uint64_t*)(host_mem + sregs->idt.base);
int i;
for (i = 0; i < 32; i++) {
struct kvm_segment gate;
gate.selector = (i * 2) << 3;
gate.type = (i & 1) ? 14 : 15;
gate.base = SEL_CS64;
gate.limit = guest_mem + ADDR_VAR_USER_CODE2;
gate.present = 1;
gate.dpl = 0;
gate.s = 0;
gate.g = 0;
gate.db = 0;
gate.l = 0;
gate.avl = 0;
fill_segment_descriptor_dword(idt, idt, &gate);
}
}

void syz_kvm_setup_vmfd(int vmfd, char *host_mem) {
const uintptr_t page_size = 4 << 10;
const uintptr_t ioapic_page = 10;
const uintptr_t guest_mem_size = 24 * page_size;
const uintptr_t guest_mem = 0;
uintptr_t i;
for (i = 0; i < guest_mem_size / page_size; i++) {
struct kvm_userspace_memory_region memreg;
memreg.slot = i;
memreg.flags = 0;
memreg.guest_phys_addr = guest_mem + i * page_size;
if (i == ioapic_page)
memreg.guest_phys_addr = 0xfec00000;
memreg.memory_size = page_size;
memreg.userspace_addr = (uintptr_t)host_mem + i * page_size;
if (vmfd != -1)
ioctl(vmfd, KVM_SET_USER_MEMORY_REGION, &memreg);
}
struct kvm_userspace_memory_region memreg;
memreg.slot = 1 + (1 << 16);
memreg.flags = 0;
memreg.guest_phys_addr = 0x30000;
memreg.memory_size = 64 << 10;
memreg.userspace_addr = (uintptr_t)host_mem;
if (vmfd != -1)
ioctl(vmfd, KVM_SET_USER_MEMORY_REGION, &memreg);
}

static uintptr_t syz_kvm_setup_cpu(int kvmfd, uintptr_t cpufd, char *host_mem)
{
const uintptr_t guest_mem = 0;
uintptr_t i;

struct kvm_sregs sregs;
if (ioctl(cpufd, KVM_GET_SREGS, &sregs))
return -1;
struct kvm_regs regs;
memset(&regs, 0, sizeof(regs));
regs.rip = guest_mem + ADDR_TEXT;
regs.rsp = ADDR_STACK0;
sregs.gdt.base = guest_mem + ADDR_GDT;
sregs.gdt.limit = 256 * sizeof(uint64_t) - 1;
uint64_t* gdt = (uint64_t*)(host_mem + sregs.gdt.base);
struct kvm_segment seg_ldt;
seg_ldt.selector = SEL_LDT;
seg_ldt.type = 2;
seg_ldt.base = guest_mem + ADDR_LDT;
seg_ldt.limit = 256 * sizeof(uint64_t) - 1;
seg_ldt.present = 1;
seg_ldt.dpl = 0;
seg_ldt.s = 0;
seg_ldt.g = 0;
seg_ldt.db = 1;
seg_ldt.l = 0;
sregs.ldt = seg_ldt;
uint64_t* ldt = (uint64_t*)(host_mem + sregs.ldt.base);
struct kvm_segment seg_cs16;
seg_cs16.selector = SEL_CS16;
seg_cs16.type = 11;
seg_cs16.base = 0;
seg_cs16.limit = 0xfffff;
seg_cs16.present = 1;
seg_cs16.dpl = 0;
seg_cs16.s = 1;
seg_cs16.g = 0;
seg_cs16.db = 0;
seg_cs16.l = 0;
struct kvm_segment seg_ds16 = seg_cs16;
seg_ds16.selector = SEL_DS16;
seg_ds16.type = 3;
struct kvm_segment seg_cs16_cpl3 = seg_cs16;
seg_cs16_cpl3.selector = SEL_CS16_CPL3;
seg_cs16_cpl3.dpl = 3;
struct kvm_segment seg_ds16_cpl3 = seg_ds16;
seg_ds16_cpl3.selector = SEL_DS16_CPL3;
seg_ds16_cpl3.dpl = 3;
struct kvm_segment seg_cs32 = seg_cs16;
seg_cs32.selector = SEL_CS32;
seg_cs32.db = 1;
struct kvm_segment seg_ds32 = seg_ds16;
seg_ds32.selector = SEL_DS32;
seg_ds32.db = 1;
struct kvm_segment seg_cs32_cpl3 = seg_cs32;
seg_cs32_cpl3.selector = SEL_CS32_CPL3;
seg_cs32_cpl3.dpl = 3;
struct kvm_segment seg_ds32_cpl3 = seg_ds32;
seg_ds32_cpl3.selector = SEL_DS32_CPL3;
seg_ds32_cpl3.dpl = 3;
struct kvm_segment seg_cs64 = seg_cs16;
seg_cs64.selector = SEL_CS64;
seg_cs64.l = 1;
struct kvm_segment seg_ds64 = seg_ds32;
seg_ds64.selector = SEL_DS64;
struct kvm_segment seg_cs64_cpl3 = seg_cs64;
seg_cs64_cpl3.selector = SEL_CS64_CPL3;
seg_cs64_cpl3.dpl = 3;
struct kvm_segment seg_ds64_cpl3 = seg_ds64;
seg_ds64_cpl3.selector = SEL_DS64_CPL3;
seg_ds64_cpl3.dpl = 3;
struct kvm_segment seg_tss32;
seg_tss32.selector = SEL_TSS32;
seg_tss32.type = 9;
seg_tss32.base = ADDR_VAR_TSS32;
seg_tss32.limit = 0x1ff;
seg_tss32.present = 1;
seg_tss32.dpl = 0;
seg_tss32.s = 0;
seg_tss32.g = 0;
seg_tss32.db = 0;
seg_tss32.l = 0;
struct kvm_segment seg_tss32_2 = seg_tss32;
seg_tss32_2.selector = SEL_TSS32_2;
seg_tss32_2.base = ADDR_VAR_TSS32_2;
struct kvm_segment seg_tss32_cpl3 = seg_tss32;
seg_tss32_cpl3.selector = SEL_TSS32_CPL3;
seg_tss32_cpl3.base = ADDR_VAR_TSS32_CPL3;
struct kvm_segment seg_tss32_vm86 = seg_tss32;
seg_tss32_vm86.selector = SEL_TSS32_VM86;
seg_tss32_vm86.base = ADDR_VAR_TSS32_VM86;
struct kvm_segment seg_tss16 = seg_tss32;
seg_tss16.selector = SEL_TSS16;
seg_tss16.base = ADDR_VAR_TSS16;
seg_tss16.limit = 0xff;
seg_tss16.type = 1;
struct kvm_segment seg_tss16_2 = seg_tss16;
seg_tss16_2.selector = SEL_TSS16_2;
seg_tss16_2.base = ADDR_VAR_TSS16_2;
seg_tss16_2.dpl = 0;
struct kvm_segment seg_tss16_cpl3 = seg_tss16;
seg_tss16_cpl3.selector = SEL_TSS16_CPL3;
seg_tss16_cpl3.base = ADDR_VAR_TSS16_CPL3;
seg_tss16_cpl3.dpl = 3;
struct kvm_segment seg_tss64 = seg_tss32;
seg_tss64.selector = SEL_TSS64;
seg_tss64.base = ADDR_VAR_TSS64;
seg_tss64.limit = 0x1ff;
struct kvm_segment seg_tss64_cpl3 = seg_tss64;
seg_tss64_cpl3.selector = SEL_TSS64_CPL3;
seg_tss64_cpl3.base = ADDR_VAR_TSS64_CPL3;
seg_tss64_cpl3.dpl = 3;
struct kvm_segment seg_cgate16;
seg_cgate16.selector = SEL_CGATE16;
seg_cgate16.type = 4;
seg_cgate16.base = SEL_CS16 | (2 << 16);
seg_cgate16.limit = ADDR_VAR_USER_CODE2;
seg_cgate16.present = 1;
seg_cgate16.dpl = 0;
seg_cgate16.s = 0;
seg_cgate16.g = 0;
seg_cgate16.db = 0;
seg_cgate16.l = 0;
seg_cgate16.avl = 0;
struct kvm_segment seg_tgate16 = seg_cgate16;
seg_tgate16.selector = SEL_TGATE16;
seg_tgate16.type = 3;
seg_cgate16.base = SEL_TSS16_2;
seg_tgate16.limit = 0;
struct kvm_segment seg_cgate32 = seg_cgate16;
seg_cgate32.selector = SEL_CGATE32;
seg_cgate32.type = 12;
seg_cgate32.base = SEL_CS32 | (2 << 16);
struct kvm_segment seg_tgate32 = seg_cgate32;
seg_tgate32.selector = SEL_TGATE32;
seg_tgate32.type = 11;
seg_tgate32.base = SEL_TSS32_2;
seg_tgate32.limit = 0;
struct kvm_segment seg_cgate64 = seg_cgate16;
seg_cgate64.selector = SEL_CGATE64;
seg_cgate64.type = 12;
seg_cgate64.base = SEL_CS64;
char buf[sizeof(struct kvm_cpuid2) + 128 * sizeof(struct kvm_cpuid_entry2)];
memset(buf, 0, sizeof(buf));
struct kvm_cpuid2* cpuid = (struct kvm_cpuid2*)buf;
cpuid->nent = 128;
ioctl(kvmfd, KVM_GET_SUPPORTED_CPUID, cpuid);
ioctl(cpufd, KVM_SET_CPUID2, cpuid);
const char* text_prefix = 0;
int text_prefix_size = 0;
char* host_text = host_mem + ADDR_TEXT;
if (1) {
sregs.efer |= EFER_LME | EFER_SCE;
sregs.cr0 |= CR0_PE;
setup_syscall_msrs(cpufd, SEL_CS64, SEL_CS64_CPL3);
setup_64bit_idt(&sregs, host_mem, guest_mem);
sregs.cs = seg_cs32;
sregs.ds = sregs.es = sregs.fs = sregs.gs = sregs.ss = seg_ds32;
uint64_t pml4_addr = guest_mem + ADDR_PML4;
uint64_t* pml4 = (uint64_t*)(host_mem + ADDR_PML4);
uint64_t pdpt_addr = guest_mem + ADDR_PDP;
uint64_t* pdpt = (uint64_t*)(host_mem + ADDR_PDP);
uint64_t pd_addr = guest_mem + ADDR_PD;
uint64_t* pd = (uint64_t*)(host_mem + ADDR_PD);
pml4[0] = PDE64_PRESENT | PDE64_RW | PDE64_USER | pdpt_addr;
pdpt[0] = PDE64_PRESENT | PDE64_RW | PDE64_USER | pd_addr;
pd[0] = PDE64_PRESENT | PDE64_RW | PDE64_USER | PDE64_PS;
sregs.cr3 = pml4_addr;
sregs.cr4 |= CR4_PAE;
if (1) {
sregs.cr0 |= CR0_NE;
*((uint64_t*)(host_mem + ADDR_VAR_VMXON_PTR)) =
ADDR_VAR_VMXON;
*((uint64_t*)(host_mem + ADDR_VAR_VMCS_PTR)) = ADDR_VAR_VMCS;
memcpy(host_mem + ADDR_VAR_VMEXIT_CODE, kvm_asm64_vm_exit,
sizeof(kvm_asm64_vm_exit) - 1);
*((uint64_t*)(host_mem + ADDR_VAR_VMEXIT_PTR)) =
ADDR_VAR_VMEXIT_CODE;
text_prefix = kvm_asm64_init_vm;
text_prefix_size = sizeof(kvm_asm64_init_vm) - 1;
}
}
struct tss16 tss16;
memset(&tss16, 0, sizeof(tss16));
tss16.ss0 = tss16.ss1 = tss16.ss2 = SEL_DS16;
tss16.sp0 = tss16.sp1 = tss16.sp2 = ADDR_STACK0;
tss16.ip = ADDR_VAR_USER_CODE2;
tss16.flags = (1 << 1);
tss16.cs = SEL_CS16;
tss16.es = tss16.ds = tss16.ss = SEL_DS16;
tss16.ldt = SEL_LDT;
struct tss16* tss16_addr = (struct tss16*)(host_mem + seg_tss16_2.base);
memcpy(tss16_addr, &tss16, sizeof(tss16));
memset(&tss16, 0, sizeof(tss16));
tss16.ss0 = tss16.ss1 = tss16.ss2 = SEL_DS16;
tss16.sp0 = tss16.sp1 = tss16.sp2 = ADDR_STACK0;
tss16.ip = ADDR_VAR_USER_CODE2;
tss16.flags = (1 << 1);
tss16.cs = SEL_CS16_CPL3;
tss16.es = tss16.ds = tss16.ss = SEL_DS16_CPL3;
tss16.ldt = SEL_LDT;
struct tss16* tss16_cpl3_addr =
(struct tss16*)(host_mem + seg_tss16_cpl3.base);
memcpy(tss16_cpl3_addr, &tss16, sizeof(tss16));
struct tss32 tss32;
memset(&tss32, 0, sizeof(tss32));
tss32.ss0 = tss32.ss1 = tss32.ss2 = SEL_DS32;
tss32.sp0 = tss32.sp1 = tss32.sp2 = ADDR_STACK0;
tss32.ip = ADDR_VAR_USER_CODE;
tss32.flags = (1 << 1) | (1 << 17);
tss32.ldt = SEL_LDT;
tss32.cr3 = sregs.cr3;
tss32.io_bitmap = offsetof(struct tss32, io_bitmap);
struct tss32* tss32_addr = (struct tss32*)(host_mem + seg_tss32_vm86.base);
memcpy(tss32_addr, &tss32, sizeof(tss32));
memset(&tss32, 0, sizeof(tss32));
tss32.ss0 = tss32.ss1 = tss32.ss2 = SEL_DS32;
tss32.sp0 = tss32.sp1 = tss32.sp2 = ADDR_STACK0;
tss32.ip = ADDR_VAR_USER_CODE;
tss32.flags = (1 << 1);
tss32.cr3 = sregs.cr3;
tss32.es = tss32.ds = tss32.ss = tss32.gs = tss32.fs = SEL_DS32;
tss32.cs = SEL_CS32;
tss32.ldt = SEL_LDT;
tss32.cr3 = sregs.cr3;
tss32.io_bitmap = offsetof(struct tss32, io_bitmap);
struct tss32* tss32_cpl3_addr = (struct tss32*)(host_mem + seg_tss32_2.base);
memcpy(tss32_cpl3_addr, &tss32, sizeof(tss32));
struct tss64 tss64;
memset(&tss64, 0, sizeof(tss64));
tss64.rsp[0] = ADDR_STACK0;
tss64.rsp[1] = ADDR_STACK0;
tss64.rsp[2] = ADDR_STACK0;
tss64.io_bitmap = offsetof(struct tss64, io_bitmap);
struct tss64* tss64_addr = (struct tss64*)(host_mem + seg_tss64.base);
memcpy(tss64_addr, &tss64, sizeof(tss64));
memset(&tss64, 0, sizeof(tss64));
tss64.rsp[0] = ADDR_STACK0;
tss64.rsp[1] = ADDR_STACK0;
tss64.rsp[2] = ADDR_STACK0;
tss64.io_bitmap = offsetof(struct tss64, io_bitmap);
struct tss64* tss64_cpl3_addr =
(struct tss64*)(host_mem + seg_tss64_cpl3.base);
memcpy(tss64_cpl3_addr, &tss64, sizeof(tss64));
if (text_prefix) {
memcpy(host_text, text_prefix, text_prefix_size);
void* patch = 0;
patch =
memmem(host_text, text_prefix_size, "\xde\xc0\xad\x0b", 4);
if (patch)
*((uint32_t*)patch) =
guest_mem + ADDR_TEXT + ((char*)patch - host_text) + 6;
uint16_t magic = PREFIX_SIZE;
patch = 0;
patch =
memmem(host_text, text_prefix_size, &magic, sizeof(magic));
if (patch)
*((uint16_t*)patch) =
guest_mem + ADDR_TEXT + text_prefix_size;
}
*(host_text + text_prefix_size) = 0xf4;
*(host_mem + ADDR_VAR_USER_CODE) = 0xf4;
*(host_mem + ADDR_VAR_HLT) = 0xf4;
memcpy(host_mem + ADDR_VAR_SYSRET, "\x0f\x07\xf4", 3);
memcpy(host_mem + ADDR_VAR_SYSEXIT, "\x0f\x35\xf4", 3);
*(uint64_t*)(host_mem + ADDR_VAR_VMWRITE_FLD) = 0;
*(uint64_t*)(host_mem + ADDR_VAR_VMWRITE_VAL) = 0;
regs.rflags |= 2;
fill_segment_descriptor(gdt, ldt, &seg_ldt);
fill_segment_descriptor(gdt, ldt, &seg_cs16);
fill_segment_descriptor(gdt, ldt, &seg_ds16);
fill_segment_descriptor(gdt, ldt, &seg_cs16_cpl3);
fill_segment_descriptor(gdt, ldt, &seg_ds16_cpl3);
fill_segment_descriptor(gdt, ldt, &seg_cs32);
fill_segment_descriptor(gdt, ldt, &seg_ds32);
fill_segment_descriptor(gdt, ldt, &seg_cs32_cpl3);
fill_segment_descriptor(gdt, ldt, &seg_ds32_cpl3);
fill_segment_descriptor(gdt, ldt, &seg_cs64);
fill_segment_descriptor(gdt, ldt, &seg_ds64);
fill_segment_descriptor(gdt, ldt, &seg_cs64_cpl3);
fill_segment_descriptor(gdt, ldt, &seg_ds64_cpl3);
fill_segment_descriptor(gdt, ldt, &seg_tss32);
fill_segment_descriptor(gdt, ldt, &seg_tss32_2);
fill_segment_descriptor(gdt, ldt, &seg_tss32_cpl3);
fill_segment_descriptor(gdt, ldt, &seg_tss32_vm86);
fill_segment_descriptor(gdt, ldt, &seg_tss16);
fill_segment_descriptor(gdt, ldt, &seg_tss16_2);
fill_segment_descriptor(gdt, ldt, &seg_tss16_cpl3);
fill_segment_descriptor_dword(gdt, ldt, &seg_tss64);
fill_segment_descriptor_dword(gdt, ldt, &seg_tss64_cpl3);
fill_segment_descriptor(gdt, ldt, &seg_cgate16);
fill_segment_descriptor(gdt, ldt, &seg_tgate16);
fill_segment_descriptor(gdt, ldt, &seg_cgate32);
fill_segment_descriptor(gdt, ldt, &seg_tgate32);
fill_segment_descriptor_dword(gdt, ldt, &seg_cgate64);
if (ioctl(cpufd, KVM_SET_SREGS, &sregs))
return -1;
if (ioctl(cpufd, KVM_SET_REGS, &regs))
return -1;
return 0;
}

int kvmfd, vmfd, vcpufd;

int main(void)
{
syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);
kvmfd = open("/dev/kvm", O_RDWR);
vmfd = ioctl(kvmfd, KVM_CREATE_VM, 0);
vcpufd = ioctl(vmfd, KVM_CREATE_VCPU, 0);
syz_kvm_setup_vmfd(vmfd, 0x20000000);
syz_kvm_setup_cpu(kvmfd, vcpufd, /*host_mem*/0x20000000);

*(uint16_t*)0x20000580 = 0;
*(uint16_t*)0x20000582 = 0;
*(uint32_t*)0x20000584 = 1040;
*(uint64_t*)0x20000588 = 0;
*(uint64_t*)0x20000590 = 0xe000; // host_mem output offset
*(uint16_t*)0x20000598 = 0;
ioctl(vcpufd, 0x4080aebf, 0x20000580);

ioctl(vcpufd, KVM_RUN, 0);
dump_buf(0x2000e000, 0x1000);
return 0;
}

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