linux-kernel - Re: [PATCH] x86/Hyper-V: Fix overflow issue in the fill_gva

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Message-ID: <CAOLK0pwEMg7kSsRNfKa6=uQ1eVGa-HdNG=qMBernoe7XwS-0_w@mail.gmail.com>
Date:   Mon, 2 Sep 2019 20:46:15 +0800
From:   Tianyu Lan <lantianyu1986@...il.com>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH] x86/Hyper-V: Fix overflow issue in the fill_gva_list()

On Sat, Aug 31, 2019 at 1:41 AM Michael Kelley <mikelley@...rosoft.com> wrote:
>
> From: lantianyu1986@...il.com  Sent: Thursday, August 29, 2019 11:16 PM
> >
> > From: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> >
> > fill_gva_list() populates gva list and adds offset
> > HV_TLB_FLUSH_UNIT(0x1000000) to variable "cur"
> > in the each loop. When diff between "end" and "cur" is
> > less than HV_TLB_FLUSH_UNIT, the gva entry should
> > be the last one and the loop should be end.
> >
> > If cur is equal or greater than 0xFF000000 on 32-bit
> > mode, "cur" will be overflow after adding HV_TLB_FLUSH_UNIT.
> > Its value will be wrapped and less than "end". fill_gva_list()
> > falls into an infinite loop and fill gva list out of
> > border finally.
> >
> > Set "cur" to be "end" to make loop end when diff is
> > less than HV_TLB_FLUSH_UNIT and add HV_TLB_FLUSH_UNIT to
> > "cur" when diff is equal or greater than HV_TLB_FLUSH_UNIT.
> > Fix the overflow issue.
>
> Let me suggest simplifying the commit message a bit.  It
> doesn't need to describe every line of the code change.   I think
> it should also make clear that the same problem could occur on
> 64-bit systems with the right "start" address.  My suggestion:
>
> When the 'start' parameter is >=  0xFF000000 on 32-bit
> systems, or >= 0xFFFFFFFF'FF000000 on 64-bit systems,
> fill_gva_list gets into an infinite loop.  With such inputs,
> 'cur' overflows after adding HV_TLB_FLUSH_UNIT and always
> compares as less than end.  Memory is filled with guest virtual
> addresses until the system crashes
>
> Fix this by never incrementing 'cur' to be larger than 'end'.
>
> >
> > Reported-by: Jong Hyun Park <park.jonghyun@...sei.ac.kr>
> > Signed-off-by: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> > Fixes: 2ffd9e33ce4a ("x86/hyper-v: Use hypercall for remote
> > TLB flush")
>
> The "Fixes:" line needs to not wrap.  It's exempt from the
> "wrap at 75 columns" rule in order to simplify parsing scripts.
>
> The code itself looks good.

Hi Michael:
       Thanks for suggestion. Update commit log in V2.
-- 
Best regards
Tianyu Lan