Re: [PATCH] KVM: X86: Fix scan ioapic use-before-initialization

[Paolo Bonzini]

On 20/11/18 09:34, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> 
> Reported by syzkaller:
> 
>  BUG: unable to handle kernel NULL pointer dereference at 00000000000001c8
>  PGD 80000003ec4da067 P4D 80000003ec4da067 PUD 3f7bfa067 PMD 0 
>  Oops: 0000 [#1] PREEMPT SMP PTI
>  CPU: 7 PID: 5059 Comm: debug Tainted: G           OE     4.19.0-rc5 #16
>  RIP: 0010:__lock_acquire+0x1a6/0x1990
>  Call Trace:
>   lock_acquire+0xdb/0x210
>   _raw_spin_lock+0x38/0x70
>   kvm_ioapic_scan_entry+0x3e/0x110 [kvm]
>   vcpu_enter_guest+0x167e/0x1910 [kvm]
>   kvm_arch_vcpu_ioctl_run+0x35c/0x610 [kvm]
>   kvm_vcpu_ioctl+0x3e9/0x6d0 [kvm]
>   do_vfs_ioctl+0xa5/0x690
>   ksys_ioctl+0x6d/0x80
>   __x64_sys_ioctl+0x1a/0x20
>   do_syscall_64+0x83/0x6e0
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> The reason is that the testcase writes hyperv synic HV_X64_MSR_SINT6 msr 
> and triggers scan ioapic logic to load synic vectors into EOI exit bitmap. 
> However, irqchip is not initialized by this simple testcase, ioapic/apic 
> objects should not be accessed.
> This can be triggered by the following program:
> 
>     #define _GNU_SOURCE
>     
>     #include <endian.h>
>     #include <stdint.h>
>     #include <stdio.h>
>     #include <stdlib.h>
>     #include <string.h>
>     #include <sys/syscall.h>
>     #include <sys/types.h>
>     #include <unistd.h>
>     
>     uint64_t r[3] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff};
>     
>     int main(void)
>     {
>     	syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);
>     	long res = 0;
>     	memcpy((void*)0x20000040, "/dev/kvm", 9);
>     	res = syscall(__NR_openat, 0xffffffffffffff9c, 0x20000040, 0, 0);
>     	if (res != -1)
>     		r[0] = res;
>     	res = syscall(__NR_ioctl, r[0], 0xae01, 0);
>     	if (res != -1)
>     		r[1] = res;
>     	res = syscall(__NR_ioctl, r[1], 0xae41, 0);
>     	if (res != -1)
>     		r[2] = res;
>     	memcpy(
>     			(void*)0x20000080,
>     			"\x01\x00\x00\x00\x00\x5b\x61\xbb\x96\x00\x00\x40\x00\x00\x00\x00\x01\x00"
>     			"\x08\x00\x00\x00\x00\x00\x0b\x77\xd1\x78\x4d\xd8\x3a\xed\xb1\x5c\x2e\x43"
>     			"\xaa\x43\x39\xd6\xff\xf5\xf0\xa8\x98\xf2\x3e\x37\x29\x89\xde\x88\xc6\x33"
>     			"\xfc\x2a\xdb\xb7\xe1\x4c\xac\x28\x61\x7b\x9c\xa9\xbc\x0d\xa0\x63\xfe\xfe"
>     			"\xe8\x75\xde\xdd\x19\x38\xdc\x34\xf5\xec\x05\xfd\xeb\x5d\xed\x2e\xaf\x22"
>     			"\xfa\xab\xb7\xe4\x42\x67\xd0\xaf\x06\x1c\x6a\x35\x67\x10\x55\xcb",
>     			106);
>     	syscall(__NR_ioctl, r[2], 0x4008ae89, 0x20000080);
>     	syscall(__NR_ioctl, r[2], 0xae80, 0);
>     	return 0;
>     }
> 
> This patch fixes it by bailing out scan ioapic if ioapic is not initialized in 
> kernel.
> 
> Reported-by: Wei Wu <ww9210@xxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> Cc: Wei Wu <ww9210@xxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> ---
>  arch/x86/kvm/x86.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 66d66d7..14b2bc4 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7455,7 +7455,8 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
>  	else {
>  		if (vcpu->arch.apicv_active)
>  			kvm_x86_ops->sync_pir_to_irr(vcpu);
> -		kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
> +		if (ioapic_in_kernel(vcpu->kvm))
> +			kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
>  	}
>  
>  	if (is_guest_mode(vcpu))
> 

Queued, thanks.

Paolo