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

[lantianyu1986@gmail.com]

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