IB/hfi1: Remove overly conservative VM_EXEC flag check

This change “IB/hfi1: Remove overly conservative VM_EXEC flag check” in Linux kernel is authored by Michael J. Ruhl <michael.j.ruhl [at] intel.com> on Thu Jan 17 12:42:04 2019 -0800.

IB/hfi1: Remove overly conservative VM_EXEC flag check

Applications that use the stack for execution purposes cause userspace PSM
jobs to fail during mmap().

Both Fortran (non-standard format parsing) and C (callback functions
located in the stack) applications can be written such that stack
execution is required. The linker notes this via the gnu_stack ELF flag.

This causes READ_IMPLIES_EXEC to be set which forces all PROT_READ mmaps
to have PROT_EXEC for the process.

Checking for VM_EXEC bit and failing the request with EPERM is overly
conservative and will break any PSM application using executable stacks.

Cc: <stable@vger.kernel.org> #v4.14+
Fixes: 12220267645c ("IB/hfi: Protect against writable mmap")
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit 7709b0d.

There are 2 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/infiniband/hw/hfi1/file_ops.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/infiniband/hw/hfi1/file_ops.c b/drivers/infiniband/hw/hfi1/file_ops.c
index c22ebc7..f9a7e9d 100644
--- a/drivers/infiniband/hw/hfi1/file_ops.c
+++ b/drivers/infiniband/hw/hfi1/file_ops.c
@@ -488,7 +488,7 @@ static int hfi1_file_mmap(struct file *fp, struct vm_area_struct *vma)
 		vmf = 1;
 		break;
 	case STATUS:
-		if (flags & (unsigned long)(VM_WRITE | VM_EXEC)) {
+		if (flags & VM_WRITE) {
 			ret = -EPERM;
 			goto done;
 		}

The commit for this change in Linux stable tree is 7709b0d (patch).

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