[PATCH] genwqe: Take R/W permissions into account when dealing with memory pages

["Guilherme G. Piccoli" <gpiccoli@linux.vnet.ibm.com>]

Currently we assume userspace pages are always writable when doing
memory pinning. This is not true, specially since userspace applications
may allocate their memory the way they want, we have no control over it.
If a read-only page is set for pinning, currently the driver fails due
to get_user_pages_fast() refusing to map read-only pages as writable.

This patch changes this behavior, by taking the permission flags of the
pages into account in both pinning/unpinning process, as well as in the
DMA data copy-back to userpace (which we shouldn't try to do blindly,
since it will fail in case of read-only-pages).

Signed-off-by: Frank Haverkamp <haver@linux.vnet.ibm.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
---

Arnd/Greg, we found this bug recently, although not critical,
it's really a boring issue affecting driver functionality.
If it's possible to take this patch still on v4.14, we'd be
really thankful!
But we know it's late, so if not possible, v4.15 is cool.

Thanks in advance!

 drivers/misc/genwqe/card_base.h  |  7 ++++++-
 drivers/misc/genwqe/card_dev.c   |  6 +++++-
 drivers/misc/genwqe/card_utils.c | 43 +++++++++++++++++++++++++---------------
 3 files changed, 38 insertions(+), 18 deletions(-)

diff --git a/drivers/misc/genwqe/card_base.h b/drivers/misc/genwqe/card_base.h
index 5813b5f25006..3743c87f8ab9 100644
--- a/drivers/misc/genwqe/card_base.h
+++ b/drivers/misc/genwqe/card_base.h
@@ -182,6 +182,7 @@ struct dma_mapping {
 
 	struct list_head card_list;	/* list of usr_maps for card */
 	struct list_head pin_list;	/* list of pinned memory for dev */
+	int write;			/* writable map? useful in unmapping */
 };
 
 static inline void genwqe_mapping_init(struct dma_mapping *m,
@@ -189,6 +190,7 @@ static inline void genwqe_mapping_init(struct dma_mapping *m,
 {
 	memset(m, 0, sizeof(*m));
 	m->type = type;
+	m->write = 1; /* Assume the maps we create are R/W */
 }
 
 /**
@@ -347,6 +349,7 @@ enum genwqe_requ_state {
  * @user_size:      size of user-space memory area
  * @page:           buffer for partial pages if needed
  * @page_dma_addr:  dma address partial pages
+ * @write:          should we write it back to userspace?
  */
 struct genwqe_sgl {
 	dma_addr_t sgl_dma_addr;
@@ -356,6 +359,8 @@ struct genwqe_sgl {
 	void __user *user_addr; /* user-space base-address */
 	size_t user_size;       /* size of memory area */
 
+	int write;
+
 	unsigned long nr_pages;
 	unsigned long fpage_offs;
 	size_t fpage_size;
@@ -369,7 +374,7 @@ struct genwqe_sgl {
 };
 
 int genwqe_alloc_sync_sgl(struct genwqe_dev *cd, struct genwqe_sgl *sgl,
-			  void __user *user_addr, size_t user_size);
+			  void __user *user_addr, size_t user_size, int write);
 
 int genwqe_setup_sgl(struct genwqe_dev *cd, struct genwqe_sgl *sgl,
 		     dma_addr_t *dma_list);
diff --git a/drivers/misc/genwqe/card_dev.c b/drivers/misc/genwqe/card_dev.c
index dd4617764f14..3ecfa35457e0 100644
--- a/drivers/misc/genwqe/card_dev.c
+++ b/drivers/misc/genwqe/card_dev.c
@@ -942,6 +942,10 @@ static int ddcb_cmd_fixups(struct genwqe_file *cfile, struct ddcb_requ *req)
 
 				genwqe_mapping_init(m,
 						    GENWQE_MAPPING_SGL_TEMP);
+
+				if (ats_flags == ATS_TYPE_SGL_RD)
+					m->write = 0;
+
 				rc = genwqe_user_vmap(cd, m, (void *)u_addr,
 						      u_size, req);
 				if (rc != 0)
@@ -954,7 +958,7 @@ static int ddcb_cmd_fixups(struct genwqe_file *cfile, struct ddcb_requ *req)
 			/* create genwqe style scatter gather list */
 			rc = genwqe_alloc_sync_sgl(cd, &req->sgls[i],
 						   (void __user *)u_addr,
-						   u_size);
+						   u_size, m->write);
 			if (rc != 0)
 				goto err_out;
 
diff --git a/drivers/misc/genwqe/card_utils.c b/drivers/misc/genwqe/card_utils.c
index 147b83011b58..5c0d917636f7 100644
--- a/drivers/misc/genwqe/card_utils.c
+++ b/drivers/misc/genwqe/card_utils.c
@@ -296,7 +296,7 @@ static int genwqe_sgl_size(int num_pages)
  * from user-space into the cached pages.
  */
 int genwqe_alloc_sync_sgl(struct genwqe_dev *cd, struct genwqe_sgl *sgl,
-			  void __user *user_addr, size_t user_size)
+			  void __user *user_addr, size_t user_size, int write)
 {
 	int rc;
 	struct pci_dev *pci_dev = cd->pci_dev;
@@ -312,6 +312,7 @@ int genwqe_alloc_sync_sgl(struct genwqe_dev *cd, struct genwqe_sgl *sgl,
 
 	sgl->user_addr = user_addr;
 	sgl->user_size = user_size;
+	sgl->write = write;
 	sgl->sgl_size = genwqe_sgl_size(sgl->nr_pages);
 
 	if (get_order(sgl->sgl_size) > MAX_ORDER) {
@@ -476,14 +477,20 @@ int genwqe_setup_sgl(struct genwqe_dev *cd, struct genwqe_sgl *sgl,
 int genwqe_free_sync_sgl(struct genwqe_dev *cd, struct genwqe_sgl *sgl)
 {
 	int rc = 0;
+	size_t offset;
+	unsigned long res;
 	struct pci_dev *pci_dev = cd->pci_dev;
 
 	if (sgl->fpage) {
-		if (copy_to_user(sgl->user_addr, sgl->fpage + sgl->fpage_offs,
-				 sgl->fpage_size)) {
-			dev_err(&pci_dev->dev, "[%s] err: copying fpage!\n",
-				__func__);
-			rc = -EFAULT;
+		if (sgl->write) {
+			res = copy_to_user(sgl->user_addr,
+				sgl->fpage + sgl->fpage_offs, sgl->fpage_size);
+			if (res) {
+				dev_err(&pci_dev->dev,
+					"[%s] err: copying fpage! (res=%lu)\n",
+					__func__, res);
+				rc = -EFAULT;
+			}
 		}
 		__genwqe_free_consistent(cd, PAGE_SIZE, sgl->fpage,
 					 sgl->fpage_dma_addr);
@@ -491,12 +498,16 @@ int genwqe_free_sync_sgl(struct genwqe_dev *cd, struct genwqe_sgl *sgl)
 		sgl->fpage_dma_addr = 0;
 	}
 	if (sgl->lpage) {
-		if (copy_to_user(sgl->user_addr + sgl->user_size -
-				 sgl->lpage_size, sgl->lpage,
-				 sgl->lpage_size)) {
-			dev_err(&pci_dev->dev, "[%s] err: copying lpage!\n",
-				__func__);
-			rc = -EFAULT;
+		if (sgl->write) {
+			offset = sgl->user_size - sgl->lpage_size;
+			res = copy_to_user(sgl->user_addr + offset, sgl->lpage,
+					   sgl->lpage_size);
+			if (res) {
+				dev_err(&pci_dev->dev,
+					"[%s] err: copying lpage! (res=%lu)\n",
+					__func__, res);
+				rc = -EFAULT;
+			}
 		}
 		__genwqe_free_consistent(cd, PAGE_SIZE, sgl->lpage,
 					 sgl->lpage_dma_addr);
@@ -599,14 +610,14 @@ int genwqe_user_vmap(struct genwqe_dev *cd, struct dma_mapping *m, void *uaddr,
 	/* pin user pages in memory */
 	rc = get_user_pages_fast(data & PAGE_MASK, /* page aligned addr */
 				 m->nr_pages,
-				 1,		/* write by caller */
+				 m->write,		/* readable/writable */
 				 m->page_list);	/* ptrs to pages */
 	if (rc < 0)
 		goto fail_get_user_pages;
 
 	/* assumption: get_user_pages can be killed by signals. */
 	if (rc < m->nr_pages) {
-		free_user_pages(m->page_list, rc, 0);
+		free_user_pages(m->page_list, rc, m->write);
 		rc = -EFAULT;
 		goto fail_get_user_pages;
 	}
@@ -618,7 +629,7 @@ int genwqe_user_vmap(struct genwqe_dev *cd, struct dma_mapping *m, void *uaddr,
 	return 0;
 
  fail_free_user_pages:
-	free_user_pages(m->page_list, m->nr_pages, 0);
+	free_user_pages(m->page_list, m->nr_pages, m->write);
 
  fail_get_user_pages:
 	kfree(m->page_list);
@@ -651,7 +662,7 @@ int genwqe_user_vunmap(struct genwqe_dev *cd, struct dma_mapping *m,
 		genwqe_unmap_pages(cd, m->dma_list, m->nr_pages);
 
 	if (m->page_list) {
-		free_user_pages(m->page_list, m->nr_pages, 1);
+		free_user_pages(m->page_list, m->nr_pages, m->write);
 
 		kfree(m->page_list);
 		m->page_list = NULL;
-- 
2.15.0.rc0