On Fri, Nov 05, 2021 at 11:16:14AM +0100, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@xxxxxxxxxx> writes:
>
> > 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@xxxxxxxxxxxxxxx
> > Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > ---
> > arch/x86/hyperv/hv_init.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> > index 24f4a06ac46a..7d252a58fbe4 100644
> > --- a/arch/x86/hyperv/hv_init.c
> > +++ b/arch/x86/hyperv/hv_init.c
> > @@ -177,6 +177,9 @@ void set_hv_tscchange_cb(void (*cb)(void))
> > return;
> > }
> >
> > + if (!hv_vp_index)
> > + return;
> > +
>
> Arguably, we could've merged this with 'if (!hv_reenlightenment_available())'
> above to get a message printed:
>
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 24f4a06ac46a..4a2a091c2f0e 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -172,7 +172,7 @@ void set_hv_tscchange_cb(void (*cb)(void))
> };
> struct hv_tsc_emulation_control emu_ctrl = {.enabled = 1};
>
> - if (!hv_reenlightenment_available()) {
> + if (!hv_reenlightenment_available() || !hv_vp_index) {
> pr_warn("Hyper-V: reenlightenment support is unavailable\n");
> return;
> }
>
> just to have an indication that something is off.
>
> > hv_reenlightenment_cb = cb;
> >
> > /* Make sure callback is registered before we write to MSRs */
>
> With or without the change,
>
> Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Thanks Sean and Vitaly. Both patches look good to me. They will be taken
via hyperv-fixes after v5.16-rc1 is cut.
Wei.
>
> --
> Vitaly
>
