[tip: x86/urgent] x86/hyper-v: Fix overflow bug in fill_gva_list()

[tip-bot2 for Tianyu Lan]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     4030b4c585c41eeefec7bd20ce3d0e100a0f2e4d
Gitweb:        https://git.kernel.org/tip/4030b4c585c41eeefec7bd20ce3d0e100a0f2e4d
Author:        Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
AuthorDate:    Mon, 02 Sep 2019 20:41:43 +08:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Mon, 02 Sep 2019 19:57:19 +02:00

x86/hyper-v: Fix overflow bug in fill_gva_list()

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@xxxxxxxxxxxx>
Signed-off-by: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Fixes: 2ffd9e33ce4a ("x86/hyper-v: Use hypercall for remote TLB flush")
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 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 e65d7fe..5208ba4 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);