KVM: x86: fix NULL deref in vcpu_scan_ioapic
commit 546d87e5c903a7f3ee7b9f998949a94729fbc65b upstream.
Reported by syzkaller:
BUG: unable to handle kernel NULL pointer dereference at 00000000000001b0
IP: _raw_spin_lock+0xc/0x30
PGD 3e28eb067
PUD 3f0ac6067
PMD 0
Oops: 0002 [#1] SMP
CPU: 0 PID: 2431 Comm: test Tainted: G OE 4.10.0-rc1+ #3
Call Trace:
? kvm_ioapic_scan_entry+0x3e/0x110 [kvm]
kvm_arch_vcpu_ioctl_run+0x10a8/0x15f0 [kvm]
? pick_next_task_fair+0xe1/0x4e0
? kvm_arch_vcpu_load+0xea/0x260 [kvm]
kvm_vcpu_ioctl+0x33a/0x600 [kvm]
? hrtimer_try_to_cancel+0x29/0x130
? do_nanosleep+0x97/0xf0
do_vfs_ioctl+0xa1/0x5d0
? __hrtimer_init+0x90/0x90
? do_nanosleep+0x5b/0xf0
SyS_ioctl+0x79/0x90
do_syscall_64+0x6e/0x180
entry_SYSCALL64_slow_path+0x25/0x25
RIP: _raw_spin_lock+0xc/0x30 RSP: ffffa43688973cc0
The syzkaller folks reported a NULL pointer dereference due to
ENABLE_CAP succeeding even without an irqchip. The Hyper-V
synthetic interrupt controller is activated, resulting in a
wrong request to rescan the ioapic and a NULL pointer dereference.
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <linux/kvm.h>
#include <pthread.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#ifndef KVM_CAP_HYPERV_SYNIC
#define KVM_CAP_HYPERV_SYNIC 123
#endif
void* thr(void* arg)
{
struct kvm_enable_cap cap;
cap.flags = 0;
cap.cap = KVM_CAP_HYPERV_SYNIC;
ioctl((long)arg, KVM_ENABLE_CAP, &cap);
return 0;
}
int main()
{
void *host_mem = mmap(0, 0x1000, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
int kvmfd = open("/dev/kvm", 0);
int vmfd = ioctl(kvmfd, KVM_CREATE_VM, 0);
struct kvm_userspace_memory_region memreg;
memreg.slot = 0;
memreg.flags = 0;
memreg.guest_phys_addr = 0;
memreg.memory_size = 0x1000;
memreg.userspace_addr = (unsigned long)host_mem;
host_mem[0] = 0xf4;
ioctl(vmfd, KVM_SET_USER_MEMORY_REGION, &memreg);
int cpufd = ioctl(vmfd, KVM_CREATE_VCPU, 0);
struct kvm_sregs sregs;
ioctl(cpufd, KVM_GET_SREGS, &sregs);
sregs.cr0 = 0;
sregs.cr4 = 0;
sregs.efer = 0;
sregs.cs.selector = 0;
sregs.cs.base = 0;
ioctl(cpufd, KVM_SET_SREGS, &sregs);
struct kvm_regs regs = { .rflags = 2 };
ioctl(cpufd, KVM_SET_REGS, ®s);
ioctl(vmfd, KVM_CREATE_IRQCHIP, 0);
pthread_t th;
pthread_create(&th, 0, thr, (void*)(long)cpufd);
usleep(rand() % 10000);
ioctl(cpufd, KVM_RUN, 0);
pthread_join(th, 0);
return 0;
}
This patch fixes it by failing ENABLE_CAP if without an irqchip.
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Fixes: 5c919412fe61 (kvm/x86: Hyper-V synthetic interrupt controller)
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 file changed