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    Subject[PATCH 4.19 308/323] x86/hyperv: Fix NULL deref in set_hv_tscchange_cb() if Hyper-V setup fails
    Date
    From: Sean Christopherson <seanjc@google.com>

    commit daf972118c517b91f74ff1731417feb4270625a4 upstream.

    Check for a valid hv_vp_index array prior to derefencing hv_vp_index when
    setting Hyper-V's TSC change callback. If Hyper-V setup failed in
    hyperv_init(), the kernel will still report that it's running under
    Hyper-V, but will have silently disabled nearly all functionality.

    BUG: kernel NULL pointer dereference, address: 0000000000000010
    #PF: supervisor read access in kernel mode
    #PF: error_code(0x0000) - not-present page
    PGD 0 P4D 0
    Oops: 0000 [#1] SMP
    CPU: 4 PID: 1 Comm: swapper/0 Not tainted 5.15.0-rc2+ #75
    Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
    RIP: 0010:set_hv_tscchange_cb+0x15/0xa0
    Code: <8b> 04 82 8b 15 12 17 85 01 48 c1 e0 20 48 0d ee 00 01 00 f6 c6 08
    ...
    Call Trace:
    kvm_arch_init+0x17c/0x280
    kvm_init+0x31/0x330
    vmx_init+0xba/0x13a
    do_one_initcall+0x41/0x1c0
    kernel_init_freeable+0x1f2/0x23b
    kernel_init+0x16/0x120
    ret_from_fork+0x22/0x30

    Fixes: 93286261de1b ("x86/hyperv: Reenlightenment notifications support")
    Cc: stable@vger.kernel.org
    Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
    Signed-off-by: Sean Christopherson <seanjc@google.com>
    Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
    Link: https://lore.kernel.org/r/20211104182239.1302956-2-seanjc@google.com
    Signed-off-by: Wei Liu <wei.liu@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/hyperv/hv_init.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/arch/x86/hyperv/hv_init.c
    +++ b/arch/x86/hyperv/hv_init.c
    @@ -200,6 +200,9 @@ void set_hv_tscchange_cb(void (*cb)(void
    return;
    }

    + if (!hv_vp_index)
    + return;
    +
    hv_reenlightenment_cb = cb;

    /* Make sure callback is registered before we write to MSRs */

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