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>
--
Vitaly
