[PATCH v2 2/4] mm: kmsan: handle alloc failures in kmsan_ioremap_page_range()

[Alexander Potapenko <glider@google.com>]

Similarly to kmsan_vmap_pages_range_noflush(),
kmsan_ioremap_page_range() must also properly handle allocation/mapping
failures. In the case of such, it must clean up the already created
metadata mappings and return an error code, so that the error can be
propagated to ioremap_page_range(). Without doing so, KMSAN may silently
fail to bring the metadata for the page range into a consistent state,
which will result in user-visible crashes when trying to access them.

Reported-by: Dipanjan Das <mail.dipanjan.das@gmail.com>
Link: https://lore.kernel.org/linux-mm/CANX2M5ZRrRA64k0hOif02TjmY9kbbO2aCBPyq79es34RXZ=cAw@mail.gmail.com/
Fixes: b073d7f8aee4 ("mm: kmsan: maintain KMSAN metadata for page operations")
Signed-off-by: Alexander Potapenko <glider@google.com>

---
v2:
 -- updated patch description as requested by Andrew Morton
 -- check the return value of __vmap_pages_range_noflush(), as suggested by Dipanjan Das
 -- return 0 from the inline version of kmsan_ioremap_page_range()
    (spotted by kernel test robot <lkp@intel.com>)
---
 include/linux/kmsan.h | 19 ++++++++-------
 mm/kmsan/hooks.c      | 55 ++++++++++++++++++++++++++++++++++++-------
 mm/vmalloc.c          |  4 ++--
 3 files changed, 59 insertions(+), 19 deletions(-)

diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h
index c7ff3aefc5a13..30b17647ce3c7 100644
--- a/include/linux/kmsan.h
+++ b/include/linux/kmsan.h
@@ -160,11 +160,12 @@ void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end);
  * @page_shift:	page_shift argument passed to vmap_range_noflush().
  *
  * KMSAN creates new metadata pages for the physical pages mapped into the
- * virtual memory.
+ * virtual memory. Returns 0 on success, callers must check for non-zero return
+ * value.
  */
-void kmsan_ioremap_page_range(unsigned long addr, unsigned long end,
-			      phys_addr_t phys_addr, pgprot_t prot,
-			      unsigned int page_shift);
+int kmsan_ioremap_page_range(unsigned long addr, unsigned long end,
+			     phys_addr_t phys_addr, pgprot_t prot,
+			     unsigned int page_shift);
 
 /**
  * kmsan_iounmap_page_range() - Notify KMSAN about a iounmap_page_range() call.
@@ -296,12 +297,12 @@ static inline void kmsan_vunmap_range_noflush(unsigned long start,
 {
 }
 
-static inline void kmsan_ioremap_page_range(unsigned long start,
-					    unsigned long end,
-					    phys_addr_t phys_addr,
-					    pgprot_t prot,
-					    unsigned int page_shift)
+static inline int kmsan_ioremap_page_range(unsigned long start,
+					   unsigned long end,
+					   phys_addr_t phys_addr, pgprot_t prot,
+					   unsigned int page_shift)
 {
+	return 0;
 }
 
 static inline void kmsan_iounmap_page_range(unsigned long start,
diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
index 3807502766a3e..ec0da72e65aa0 100644
--- a/mm/kmsan/hooks.c
+++ b/mm/kmsan/hooks.c
@@ -148,35 +148,74 @@ void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end)
  * into the virtual memory. If those physical pages already had shadow/origin,
  * those are ignored.
  */
-void kmsan_ioremap_page_range(unsigned long start, unsigned long end,
-			      phys_addr_t phys_addr, pgprot_t prot,
-			      unsigned int page_shift)
+int kmsan_ioremap_page_range(unsigned long start, unsigned long end,
+			     phys_addr_t phys_addr, pgprot_t prot,
+			     unsigned int page_shift)
 {
 	gfp_t gfp_mask = GFP_KERNEL | __GFP_ZERO;
 	struct page *shadow, *origin;
 	unsigned long off = 0;
-	int nr;
+	int nr, err = 0, clean = 0, mapped;
 
 	if (!kmsan_enabled || kmsan_in_runtime())
-		return;
+		return 0;
 
 	nr = (end - start) / PAGE_SIZE;
 	kmsan_enter_runtime();
-	for (int i = 0; i < nr; i++, off += PAGE_SIZE) {
+	for (int i = 0; i < nr; i++, off += PAGE_SIZE, clean = i) {
 		shadow = alloc_pages(gfp_mask, 1);
 		origin = alloc_pages(gfp_mask, 1);
-		__vmap_pages_range_noflush(
+		if (!shadow || !origin) {
+			err = -ENOMEM;
+			goto ret;
+		}
+		mapped = __vmap_pages_range_noflush(
 			vmalloc_shadow(start + off),
 			vmalloc_shadow(start + off + PAGE_SIZE), prot, &shadow,
 			PAGE_SHIFT);
-		__vmap_pages_range_noflush(
+		if (mapped) {
+			err = mapped;
+			goto ret;
+		}
+		shadow = NULL;
+		mapped = __vmap_pages_range_noflush(
 			vmalloc_origin(start + off),
 			vmalloc_origin(start + off + PAGE_SIZE), prot, &origin,
 			PAGE_SHIFT);
+		if (mapped) {
+			__vunmap_range_noflush(
+				vmalloc_shadow(start + off),
+				vmalloc_shadow(start + off + PAGE_SIZE));
+			err = mapped;
+			goto ret;
+		}
+		origin = NULL;
+	}
+	/* Page mapping loop finished normally, nothing to clean up. */
+	clean = 0;
+
+ret:
+	if (clean > 0) {
+		/*
+		 * Something went wrong. Clean up shadow/origin pages allocated
+		 * on the last loop iteration, then delete mappings created
+		 * during the previous iterations.
+		 */
+		if (shadow)
+			__free_pages(shadow, 1);
+		if (origin)
+			__free_pages(origin, 1);
+		__vunmap_range_noflush(
+			vmalloc_shadow(start),
+			vmalloc_shadow(start + clean * PAGE_SIZE));
+		__vunmap_range_noflush(
+			vmalloc_origin(start),
+			vmalloc_origin(start + clean * PAGE_SIZE));
 	}
 	flush_cache_vmap(vmalloc_shadow(start), vmalloc_shadow(end));
 	flush_cache_vmap(vmalloc_origin(start), vmalloc_origin(end));
 	kmsan_leave_runtime();
+	return err;
 }
 
 void kmsan_iounmap_page_range(unsigned long start, unsigned long end)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 1355d95cce1ca..31ff782d368b0 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -313,8 +313,8 @@ int ioremap_page_range(unsigned long addr, unsigned long end,
 				 ioremap_max_page_shift);
 	flush_cache_vmap(addr, end);
 	if (!err)
-		kmsan_ioremap_page_range(addr, end, phys_addr, prot,
-					 ioremap_max_page_shift);
+		err = kmsan_ioremap_page_range(addr, end, phys_addr, prot,
+					       ioremap_max_page_shift);
 	return err;
 }
 
-- 
2.40.0.577.gac1e443424-goog