On Sat, Aug 31, 2019 at 1:41 AM Michael Kelley <mikel...@microsoft.com> wrote:
>
> From: lantianyu1...@gmail.com Sent: Thursday, August 29, 2019 11:16 PM
> >
> > From: Tianyu Lan <tianyu....@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.jongh...@yonsei.ac.kr>
> > Signed-off-by: Tianyu Lan <tianyu....@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
