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

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

[lantianyu1986]

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.

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")
---
 arch/x86/hyperv/mmu.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c
index e65d7fe6489f..5208ba49c89a 100644
--- a/arch/x86/hyperv/mmu.c
+++ b/arch/x86/hyperv/mmu.c
@@ -37,12 +37,14 @@ static inline int fill_gva_list(u64 gva_list[], int offset,
 		 * Lower 12 bits encode the number of additional
 		 * pages to flush (in addition to the 'cur' page).
 		 */
-		if (diff >= HV_TLB_FLUSH_UNIT)
+		if (diff >= HV_TLB_FLUSH_UNIT) {
 			gva_list[gva_n] |= ~PAGE_MASK;
-		else if (diff)
+			cur += HV_TLB_FLUSH_UNIT;
+		}  else if (diff) {
 			gva_list[gva_n] |= (diff - 1) >> PAGE_SHIFT;
+			cur = end;
+		}
 
-		cur += HV_TLB_FLUSH_UNIT;
 		gva_n++;
 
 	} while (cur < end);
-- 
2.14.5

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

[Michael Kelley]

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

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

[Tianyu Lan]

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