Re: [PATCH] kvm: use PIT channel index in hpet_legacy_start mode

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+-- On Thu, 7 Jan 2016, Paolo Bonzini wrote --+
| > Will this trigger the same issue like CVE-2015-7513 ?
| > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=0185604c2d82c560dab2f2933a18f797e74ab5a8
| 
| I am not sure (--verbose please :))

  IIUC, it shouldn't, because pit_load_count() does

    /*
     * The largest possible initial count is 0; this is equivalent
     * to 216 for binary counting and 104 for BCD counting.
     */
    if (val == 0)
        val = 0x10000;


| but the right fix is to change the caller like this:
 
| diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
| @@ -420,6 +420,7 @@ void kvm_pit_load_count(struct kvm *kvm, int channel, u32 val, int hpet_legacy_s
|  	u8 saved_mode;
|  	if (hpet_legacy_start) {
|  		/* save existing mode for later reenablement */
| +		WARN_ON(channel != 0);
|  		saved_mode = kvm->arch.vpit->pit_state.channels[0].mode;
|  		kvm->arch.vpit->pit_state.channels[0].mode = 0xff; /* disable timer */
|  		pit_load_count(kvm, channel, val);

  In that case I guess, 'pit_load_count' could be called as

+               pit_load_count(kvm, 0, val); 


Thank you.
--
 - P J P
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F
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