Re: [PATCH] x86/Hyper-V: Fix overflow issue in the fill_gva_list()

From: Tianyu Lan <lantianyu1986@gmail.com>
To: Michael Kelley <mikelley@microsoft.com>
Cc: KY Srinivasan <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	"sashal@kernel.org" <sashal@kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"bp@alien8.de" <bp@alien8.de>, "hpa@zytor.com" <hpa@zytor.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	"cohuck@redhat.com" <cohuck@redhat.com>,
	Tianyu Lan <Tianyu.Lan@microsoft.com>,
	"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: [PATCH] x86/Hyper-V: Fix overflow issue in the fill_gva_list()
Date: Mon, 2 Sep 2019 20:46:15 +0800	[thread overview]
Message-ID: <CAOLK0pwEMg7kSsRNfKa6=uQ1eVGa-HdNG=qMBernoe7XwS-0_w@mail.gmail.com> (raw)
In-Reply-To: <DM5PR21MB0137B7C2AAD0FC65CB3E1306D7BD0@DM5PR21MB0137.namprd21.prod.outlook.com>

On Sat, Aug 31, 2019 at 1:41 AM Michael Kelley <mikelley@microsoft.com> wrote:
>
> From: lantianyu1986@gmail.com  Sent: Thursday, August 29, 2019 11:16 PM
> >
> > From: Tianyu Lan <Tianyu.Lan@microsoft.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@yonsei.ac.kr>
> > Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.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