[PATCH 1/2] mm: kmsan: handle alloc failures in kmsan_vmap_pages_range_noflush()

[Alexander Potapenko]

As reported by Dipanjan Das, when KMSAN is used together with kernel
fault injection (or, generally, even without the latter), calls to
kcalloc() or __vmap_pages_range_noflush() may fail, leaving the
metadata mappings for the virtual mapping in an inconsistent state.
When these metadata mappings are accessed later, the kernel crashes.

To address the problem, we return a non-zero error code from
kmsan_vmap_pages_range_noflush() in the case of any allocation/mapping
failure inside it, and make vmap_pages_range_noflush() return an error
if KMSAN fails to allocate the metadata.

This patch also removes KMSAN_WARN_ON() from vmap_pages_range_noflush(),
as these allocation failures are not fatal anymore.

Reported-by: Dipanjan Das <mail.dipanjan.das@xxxxxxxxx>
Link: https://lore.kernel.org/linux-mm/CANX2M5ZRrRA64k0hOif02TjmY9kbbO2aCBPyq79es34RXZ=cAw@xxxxxxxxxxxxxx/
Fixes: b073d7f8aee4 ("mm: kmsan: maintain KMSAN metadata for page operations")
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
---
 include/linux/kmsan.h | 19 ++++++++++---------
 mm/kmsan/shadow.c     | 27 ++++++++++++++++++---------
 mm/vmalloc.c          |  6 +++++-
 3 files changed, 33 insertions(+), 19 deletions(-)

diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h
index e38ae3c346184..a0769d4aad1c8 100644
--- a/include/linux/kmsan.h
+++ b/include/linux/kmsan.h
@@ -134,11 +134,12 @@ void kmsan_kfree_large(const void *ptr);
  * @page_shift:	page_shift passed to vmap_range_noflush().
  *
  * KMSAN maps shadow and origin pages of @pages into contiguous ranges in
- * vmalloc metadata address range.
+ * vmalloc metadata address range. Returns 0 on success, callers must check
+ * for non-zero return value.
  */
-void kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,
-				    pgprot_t prot, struct page **pages,
-				    unsigned int page_shift);
+int kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,
+				   pgprot_t prot, struct page **pages,
+				   unsigned int page_shift);
 
 /**
  * kmsan_vunmap_kernel_range_noflush() - Notify KMSAN about a vunmap.
@@ -281,11 +282,11 @@ static inline void kmsan_kfree_large(const void *ptr)
 {
 }
 
-static inline void kmsan_vmap_pages_range_noflush(unsigned long start,
-						  unsigned long end,
-						  pgprot_t prot,
-						  struct page **pages,
-						  unsigned int page_shift)
+static inline int kmsan_vmap_pages_range_noflush(unsigned long start,
+						 unsigned long end,
+						 pgprot_t prot,
+						 struct page **pages,
+						 unsigned int page_shift)
 {
 }
 
diff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c
index a787c04e9583c..b8bb95eea5e3d 100644
--- a/mm/kmsan/shadow.c
+++ b/mm/kmsan/shadow.c
@@ -216,27 +216,29 @@ void kmsan_free_page(struct page *page, unsigned int order)
 	kmsan_leave_runtime();
 }
 
-void kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,
-				    pgprot_t prot, struct page **pages,
-				    unsigned int page_shift)
+int kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,
+				   pgprot_t prot, struct page **pages,
+				   unsigned int page_shift)
 {
 	unsigned long shadow_start, origin_start, shadow_end, origin_end;
 	struct page **s_pages, **o_pages;
-	int nr, mapped;
+	int nr, mapped, err = 0;
 
 	if (!kmsan_enabled)
-		return;
+		return 0;
 
 	shadow_start = vmalloc_meta((void *)start, KMSAN_META_SHADOW);
 	shadow_end = vmalloc_meta((void *)end, KMSAN_META_SHADOW);
 	if (!shadow_start)
-		return;
+		return 0;
 
 	nr = (end - start) / PAGE_SIZE;
 	s_pages = kcalloc(nr, sizeof(*s_pages), GFP_KERNEL);
 	o_pages = kcalloc(nr, sizeof(*o_pages), GFP_KERNEL);
-	if (!s_pages || !o_pages)
+	if (!s_pages || !o_pages) {
+		err = -ENOMEM;
 		goto ret;
+	}
 	for (int i = 0; i < nr; i++) {
 		s_pages[i] = shadow_page_for(pages[i]);
 		o_pages[i] = origin_page_for(pages[i]);
@@ -249,10 +251,16 @@ void kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,
 	kmsan_enter_runtime();
 	mapped = __vmap_pages_range_noflush(shadow_start, shadow_end, prot,
 					    s_pages, page_shift);
-	KMSAN_WARN_ON(mapped);
+	if (mapped) {
+		err = mapped;
+		goto ret;
+	}
 	mapped = __vmap_pages_range_noflush(origin_start, origin_end, prot,
 					    o_pages, page_shift);
-	KMSAN_WARN_ON(mapped);
+	if (mapped) {
+		err = mapped;
+		goto ret;
+	}
 	kmsan_leave_runtime();
 	flush_tlb_kernel_range(shadow_start, shadow_end);
 	flush_tlb_kernel_range(origin_start, origin_end);
@@ -262,6 +270,7 @@ void kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,
 ret:
 	kfree(s_pages);
 	kfree(o_pages);
+	return err;
 }
 
 /* Allocate metadata for pages allocated at boot time. */
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a50072066221a..1355d95cce1ca 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -605,7 +605,11 @@ int __vmap_pages_range_noflush(unsigned long addr, unsigned long end,
 int vmap_pages_range_noflush(unsigned long addr, unsigned long end,
 		pgprot_t prot, struct page **pages, unsigned int page_shift)
 {
-	kmsan_vmap_pages_range_noflush(addr, end, prot, pages, page_shift);
+	int ret = kmsan_vmap_pages_range_noflush(addr, end, prot, pages,
+						 page_shift);
+
+	if (ret)
+		return ret;
 	return __vmap_pages_range_noflush(addr, end, prot, pages, page_shift);
 }
 
-- 
2.40.0.577.gac1e443424-goog