linux-kernel - Re: [PATCH] KVM: arm64: Fix 64 bit mmio handle

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Date:   Wed, 06 Jul 2022 19:29:58 +0800
From:   Schspa Shi <schspa@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Fix 64 bit mmio handle


Marc Zyngier <maz@...nel.org> writes:

> On Fri, 01 Jul 2022 15:22:51 +0100,
> Schspa Shi <schspa@...il.com> wrote:
>> 
>> 
>> Marc Zyngier <maz@...nel.org> writes:
>> 
>> >> 
>> >> I have running some static code analysis software upon 
>> >> Kernel code.
>> >> Seeing there is possible overflow.
>> >> 
>> >> maks << 1U << ((len * 8) -1);
>> >> 
>> >> The AI don't know, len is only the value of 1, 2, 4, and 
>> >> make this
>> >> a warnings
>> >> 
>> >> I tring to analysis this, but didn't realize the real 
>> >> scenario of
>> >> sign extension, and finally sent this problematic patch.
>> >> 
>> >> I do see some uninitialized memory reads (the values are not 
>> >> used
>> >> in the end, just as temporary space for API execution),
>> >> do we need to fix these?
>> > 
>> > You need to be more descriptive here. What uninitialised 
>> > reads? In
>> > general, pointing at the code and providing a full 
>> > description of
>> > what
>> > you think is incorrect would really help...
>> > 
>> > 	M.
>> One example is
>> int vgic_v3_has_attr_regs(struct kvm_device *dev, struct
>> kvm_device_attr *attr)
>> {
>> 	...
>>    case KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS: {
>> 		u64 reg, id;
>> 
>> 		id = (attr->attr & KVM_DEV_ARM_VGIC_SYSREG_INSTR_MASK);
>> 		return vgic_v3_has_cpu_sysregs_attr(vcpu, 0, id, &reg);
>> 	}
>> 
>> }
>> 
>> The funcion vgic_v3_has_cpu_sysregs_attr will read reg's value 
>> to
>> params without initialization. There should have no problems,
>> because the register value never used.
>
> Thanks for pointing this out.
>
> I spent some time looking at this, and this is only the tip of 
> the
> iceberg. The whole userspace interaction with the GIC sysregs is 
> ugly
> (at best), and needs some love.
>
> I've written a small series[1] cleaning things up, which needs 
> testing
> (I've just checked that it was compiling correctly). I'd 
> appreciate
> you running your tool on it.
>

I have run static code analysis software upon this branch, and the
warnings have gone.

> 	M.
>
> [1] 
> https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/sysreg-cleanup-5.20


-- 
BRs
Schspa Shi