[PATCH v2 25/34] kasan, vmalloc: don't unpoison VM_ALLOC pages before mapping

[andrey.konovalov@linux.dev]

From: Andrey Konovalov <andreyknvl@google.com>

This patch makes KASAN unpoison vmalloc mappings after that have been
mapped in when it's possible: for vmalloc() (indentified via VM_ALLOC)
and vm_map_ram().

The reasons for this are:

- For vmalloc() and vm_map_ram(): pages don't get unpoisoned in case
  mapping them fails.
- For vmalloc(): HW_TAGS KASAN needs pages to be mapped to set tags via
  kasan_unpoison_vmalloc().

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/vmalloc.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index f37d0ed99bf9..82ef1e27e2e4 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2208,14 +2208,15 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node)
 		mem = (void *)addr;
 	}
 
-	mem = kasan_unpoison_vmalloc(mem, size);
-
 	if (vmap_pages_range(addr, addr + size, PAGE_KERNEL,
 				pages, PAGE_SHIFT) < 0) {
 		vm_unmap_ram(mem, count);
 		return NULL;
 	}
 
+	/* Mark the pages as accessible after they were mapped in. */
+	mem = kasan_unpoison_vmalloc(mem, size);
+
 	return mem;
 }
 EXPORT_SYMBOL(vm_map_ram);
@@ -2443,7 +2444,14 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
 
 	setup_vmalloc_vm(area, va, flags, caller);
 
-	area->addr = kasan_unpoison_vmalloc(area->addr, requested_size);
+	/*
+	 * For VM_ALLOC mappings, __vmalloc_node_range() mark the pages as
+	 * accessible after they are mapped in.
+	 * Otherwise, as the pages can be mapped outside of vmalloc code,
+	 * mark them now as a best-effort approach.
+	 */
+	if (!(flags & VM_ALLOC))
+		area->addr = kasan_unpoison_vmalloc(area->addr, requested_size);
 
 	return area;
 }
@@ -3072,6 +3080,12 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 	if (!addr)
 		goto fail;
 
+	/*
+	 * Mark the pages for VM_ALLOC mappings as accessible after they were
+	 * mapped in.
+	 */
+	addr = kasan_unpoison_vmalloc(addr, real_size);
+
 	/*
 	 * In this function, newly allocated vm_struct has VM_UNINITIALIZED
 	 * flag. It means that vm_struct is not fully initialized.
@@ -3766,7 +3780,11 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 	}
 	spin_unlock(&vmap_area_lock);
 
-	/* mark allocated areas as accessible */
+	/*
+	 * Mark allocated areas as accessible.
+	 * As the pages are mapped outside of vmalloc code,
+	 * mark them now as a best-effort approach.
+	 */
 	for (area = 0; area < nr_vms; area++)
 		vms[area]->addr = kasan_unpoison_vmalloc(vms[area]->addr,
 							 vms[area]->size);
-- 
2.25.1