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SubjectRe: [PATCH] KVM: X86: Fix scan ioapic use-before-initialization
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On 20/11/18 09:34, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> 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@gmail.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Wei Wu <ww9210@gmail.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> 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

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