[PATCH 3.19.y-ckt 025/107] cxl: Fix off by one error allowing subsequent mmap page to be accessed

[Kamal Mostafa]

3.19.8-ckt5 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ian Munsie <imunsie at au1.ibm.com>

commit 10a5894f2dedd8a26b3132497445b314c0d952c4 upstream.

It was discovered that if a process mmaped their problem state area they
were able to access one page more than expected, potentially allowing
them to access the problem state area of an unrelated process.

This was due to a simple off by one error in the mmap fault handler
introduced in 0712dc7e73e59d79bcead5d5520acf4e9e917e87 ("cxl: Fix issues
when unmapping contexts"), which is fixed in this patch.

Fixes: 0712dc7e73e5 ("cxl: Fix issues when unmapping contexts")
Signed-off-by: Ian Munsie <imunsie at au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/misc/cxl/context.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/cxl/context.c b/drivers/misc/cxl/context.c
index d1b55fe..e4dc8cd 100644
--- a/drivers/misc/cxl/context.c
+++ b/drivers/misc/cxl/context.c
@@ -113,11 +113,11 @@ static int cxl_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 
 	if (ctx->afu->current_mode == CXL_MODE_DEDICATED) {
 		area = ctx->afu->psn_phys;
-		if (offset > ctx->afu->adapter->ps_size)
+		if (offset >= ctx->afu->adapter->ps_size)
 			return VM_FAULT_SIGBUS;
 	} else {
 		area = ctx->psn_phys;
-		if (offset > ctx->psn_size)
+		if (offset >= ctx->psn_size)
 			return VM_FAULT_SIGBUS;
 	}
 
-- 
1.9.1