Messages in this thread | | | From | Michael Kelley <> | Subject | RE: [PATCH] x86/Hyper-V: Fix overflow issue in the fill_gva_list() | Date | Fri, 30 Aug 2019 17:41:06 +0000 |
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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.
Michael
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