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From: Dan Carpenter <dan.carpenter@oracle.com>
To: kbuild@lists.01.org
Subject: Re: arch/x86/kvm/x86.c:4988 kvm_arch_tsc_set_attr() warn: check for integer overflow 'offset'
Date: Wed, 12 Oct 2022 09:34:18 +0300	[thread overview]
Message-ID: <Y0Zf6g7ahY2b7MBK@kadam> (raw)
In-Reply-To: <2c36799c-af38-fed5-3f31-a8bde25368d7@redhat.com>

[-- Attachment #1: Type: text/plain, Size: 1064 bytes --]

On Tue, Oct 11, 2022 at 03:02:28PM +0200, Paolo Bonzini wrote:
> On 10/10/22 20:39, Sean Christopherson wrote:
> > > 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.
> > 
> > This is ok, and even necessary, e.g. if the host TSC > guest TSC.
> 
> (which in fact is the common case).  Also this is unsigned which is fine
> according to the C standard, though I understand that static analyzers want
> to be stricter.
> 
> > Is there anything
> > we can do in KVM to help Smatch avoid false positives?  Or do you/Smatch already
> > maintain a list of known false positives?
> 
> Seconded.

Thanks for your feedback.

I could probably make a rule to ignore clock related stuff.  That's
honestly been a known source of false positives for a while.  I kind of
have the infrastructure so it's not super hard to do actually... I'll do
that.

regards,
dan carpenter

WARNING: multiple messages have this Message-ID (diff)
From: Dan Carpenter <dan.carpenter@oracle.com>
To: kbuild-all@lists.01.org
Subject: Re: [kbuild] arch/x86/kvm/x86.c:4988 kvm_arch_tsc_set_attr() warn: check for integer overflow 'offset'
Date: Wed, 12 Oct 2022 09:34:18 +0300	[thread overview]
Message-ID: <Y0Zf6g7ahY2b7MBK@kadam> (raw)
In-Reply-To: <2c36799c-af38-fed5-3f31-a8bde25368d7@redhat.com>

[-- Attachment #1: Type: text/plain, Size: 1064 bytes --]

On Tue, Oct 11, 2022 at 03:02:28PM +0200, Paolo Bonzini wrote:
> On 10/10/22 20:39, Sean Christopherson wrote:
> > > 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.
> > 
> > This is ok, and even necessary, e.g. if the host TSC > guest TSC.
> 
> (which in fact is the common case).  Also this is unsigned which is fine
> according to the C standard, though I understand that static analyzers want
> to be stricter.
> 
> > Is there anything
> > we can do in KVM to help Smatch avoid false positives?  Or do you/Smatch already
> > maintain a list of known false positives?
> 
> Seconded.

Thanks for your feedback.

I could probably make a rule to ignore clock related stuff.  That's
honestly been a known source of false positives for a while.  I kind of
have the infrastructure so it's not super hard to do actually... I'll do
that.

regards,
dan carpenter

WARNING: multiple messages have this Message-ID (diff)
From: Dan Carpenter <dan.carpenter@oracle.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
	kbuild@lists.01.org, Oliver Upton <oupton@google.com>,
	lkp@intel.com, kbuild-all@lists.01.org,
	linux-kernel@vger.kernel.org
Subject: Re: [kbuild] arch/x86/kvm/x86.c:4988 kvm_arch_tsc_set_attr() warn: check for integer overflow 'offset'
Date: Wed, 12 Oct 2022 09:34:18 +0300	[thread overview]
Message-ID: <Y0Zf6g7ahY2b7MBK@kadam> (raw)
In-Reply-To: <2c36799c-af38-fed5-3f31-a8bde25368d7@redhat.com>

On Tue, Oct 11, 2022 at 03:02:28PM +0200, Paolo Bonzini wrote:
> On 10/10/22 20:39, Sean Christopherson wrote:
> > > 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.
> > 
> > This is ok, and even necessary, e.g. if the host TSC > guest TSC.
> 
> (which in fact is the common case).  Also this is unsigned which is fine
> according to the C standard, though I understand that static analyzers want
> to be stricter.
> 
> > Is there anything
> > we can do in KVM to help Smatch avoid false positives?  Or do you/Smatch already
> > maintain a list of known false positives?
> 
> Seconded.

Thanks for your feedback.

I could probably make a rule to ignore clock related stuff.  That's
honestly been a known source of false positives for a while.  I kind of
have the infrastructure so it's not super hard to do actually... I'll do
that.

regards,
dan carpenter


  reply	other threads:[~2022-10-12  6:34 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-10 13:56 arch/x86/kvm/x86.c:4988 kvm_arch_tsc_set_attr() warn: check for integer overflow 'offset' kernel test robot
2022-10-10 14:15 ` [kbuild] " Dan Carpenter
2022-10-10 14:15 ` Dan Carpenter
2022-10-10 18:39 ` Sean Christopherson
2022-10-10 18:39   ` Sean Christopherson
2022-10-11 13:02   ` Paolo Bonzini
2022-10-11 13:02     ` Paolo Bonzini
2022-10-12  6:34     ` Dan Carpenter [this message]
2022-10-12  6:34       ` Dan Carpenter
2022-10-12  6:34       ` Dan Carpenter
  -- strict thread matches above, loose matches on Subject: below --
2022-08-10  6:18 kernel test robot
2022-08-09  3:21 kernel test robot
2022-08-08 14:20 kernel test robot

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