linux-kernel - [kbuild] arch/x86/kvm/x86.c:4988 kvm_arch_tsc_set_attr() warn: check for integer overflow 'offset'

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Date:   Mon, 10 Oct 2022 17:15:40 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     kbuild@...ts.01.org, Oliver Upton <oupton@...gle.com>
Cc:     lkp@...el.com, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: [kbuild] arch/x86/kvm/x86.c:4988 kvm_arch_tsc_set_attr() warn: check
 for integer overflow 'offset'

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git   master
head:   493ffd6605b2d3d4dc7008ab927dba319f36671f
commit: 828ca89628bfcb1b8f27535025f69dd00eb55207 KVM: x86: Expose TSC offset controls to userspace
config: x86_64-randconfig-m001-20221010
compiler: gcc-11 (Debian 11.3.0-5) 11.3.0

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@...el.com>
| Reported-by: Dan Carpenter <dan.carpenter@...cle.com>

smatch warnings:
arch/x86/kvm/x86.c:4988 kvm_arch_tsc_set_attr() warn: check for integer overflow 'offset'

vim +/offset +4988 arch/x86/kvm/x86.c

828ca89628bfcb Oliver Upton 2021-09-16  4962  static int kvm_arch_tsc_set_attr(struct kvm_vcpu *vcpu,
828ca89628bfcb Oliver Upton 2021-09-16  4963  				 struct kvm_device_attr *attr)
828ca89628bfcb Oliver Upton 2021-09-16  4964  {
828ca89628bfcb Oliver Upton 2021-09-16  4965  	u64 __user *uaddr = (u64 __user *)(unsigned long)attr->addr;
828ca89628bfcb Oliver Upton 2021-09-16  4966  	struct kvm *kvm = vcpu->kvm;
828ca89628bfcb Oliver Upton 2021-09-16  4967  	int r;
828ca89628bfcb Oliver Upton 2021-09-16  4968  
828ca89628bfcb Oliver Upton 2021-09-16  4969  	if ((u64)(unsigned long)uaddr != attr->addr)
828ca89628bfcb Oliver Upton 2021-09-16  4970  		return -EFAULT;
828ca89628bfcb Oliver Upton 2021-09-16  4971  
828ca89628bfcb Oliver Upton 2021-09-16  4972  	switch (attr->attr) {
828ca89628bfcb Oliver Upton 2021-09-16  4973  	case KVM_VCPU_TSC_OFFSET: {
828ca89628bfcb Oliver Upton 2021-09-16  4974  		u64 offset, tsc, ns;
828ca89628bfcb Oliver Upton 2021-09-16  4975  		unsigned long flags;
828ca89628bfcb Oliver Upton 2021-09-16  4976  		bool matched;
828ca89628bfcb Oliver Upton 2021-09-16  4977  
828ca89628bfcb Oliver Upton 2021-09-16  4978  		r = -EFAULT;
828ca89628bfcb Oliver Upton 2021-09-16  4979  		if (get_user(offset, uaddr))
828ca89628bfcb Oliver Upton 2021-09-16  4980  			break;
828ca89628bfcb Oliver Upton 2021-09-16  4981  
828ca89628bfcb Oliver Upton 2021-09-16  4982  		raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
828ca89628bfcb Oliver Upton 2021-09-16  4983  
828ca89628bfcb Oliver Upton 2021-09-16  4984  		matched = (vcpu->arch.virtual_tsc_khz &&
828ca89628bfcb Oliver Upton 2021-09-16  4985  			   kvm->arch.last_tsc_khz == vcpu->arch.virtual_tsc_khz &&
828ca89628bfcb Oliver Upton 2021-09-16  4986  			   kvm->arch.last_tsc_offset == offset);
828ca89628bfcb Oliver Upton 2021-09-16  4987  
828ca89628bfcb Oliver Upton 2021-09-16 @4988  		tsc = kvm_scale_tsc(vcpu, rdtsc(), vcpu->arch.l1_tsc_scaling_ratio) + offset;

Smatch hates obvious user triggerable integer overflows...  No checking
on offset.

828ca89628bfcb Oliver Upton 2021-09-16  4989  		ns = get_kvmclock_base_ns();
828ca89628bfcb Oliver Upton 2021-09-16  4990  
828ca89628bfcb Oliver Upton 2021-09-16  4991  		__kvm_synchronize_tsc(vcpu, offset, tsc, ns, matched);
828ca89628bfcb Oliver Upton 2021-09-16  4992  		raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
828ca89628bfcb Oliver Upton 2021-09-16  4993  
828ca89628bfcb Oliver Upton 2021-09-16  4994  		r = 0;
828ca89628bfcb Oliver Upton 2021-09-16  4995  		break;
828ca89628bfcb Oliver Upton 2021-09-16  4996  	}
828ca89628bfcb Oliver Upton 2021-09-16  4997  	default:
828ca89628bfcb Oliver Upton 2021-09-16  4998  		r = -ENXIO;
828ca89628bfcb Oliver Upton 2021-09-16  4999  	}
828ca89628bfcb Oliver Upton 2021-09-16  5000  
828ca89628bfcb Oliver Upton 2021-09-16  5001  	return r;
828ca89628bfcb Oliver Upton 2021-09-16  5002  }