lib/test_kasan.c: add roundtrip tests

In several places we need to be able to operate on pointers which have
gone via a roundtrip:

	virt -> {phys,page} -> virt

With KASAN_SW_TAGS, we can't preserve the tag for SLUB objects, and the
{phys,page} -> virt conversion will use KASAN_TAG_KERNEL.

This patch adds tests to ensure that this works as expected, without
false positives which have recently been spotted [1,2] in testing.

[1] https://lore.kernel.org/linux-arm-kernel/[email protected]/
[2] https://lore.kernel.org/linux-arm-kernel/[email protected]/

[[email protected]: coding-style fixes]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Mark Rutland <[email protected]>
Reviewed-by: Andrey Konovalov <[email protected]>
Tested-by: Andrey Konovalov <[email protected]>
Acked-by: Andrey Ryabinin <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

lib/test_kasan.c

@@ -18,6 +18,9 @@
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/uaccess.h>
+#include <linux/io.h>
+
+#include <asm/page.h>
 
 /*
  * Note: test functions are marked noinline so that their names appear in
@@ -337,6 +340,42 @@ static noinline void __init kmalloc_uaf2(void)
 	kfree(ptr2);
 }
 
+static noinline void __init kfree_via_page(void)
+{
+	char *ptr;
+	size_t size = 8;
+	struct page *page;
+	unsigned long offset;
+
+	pr_info("invalid-free false positive (via page)\n");
+	ptr = kmalloc(size, GFP_KERNEL);
+	if (!ptr) {
+		pr_err("Allocation failed\n");
+		return;
+	}
+
+	page = virt_to_page(ptr);
+	offset = offset_in_page(ptr);
+	kfree(page_address(page) + offset);
+}
+
+static noinline void __init kfree_via_phys(void)
+{
+	char *ptr;
+	size_t size = 8;
+	phys_addr_t phys;
+
+	pr_info("invalid-free false positive (via phys)\n");
+	ptr = kmalloc(size, GFP_KERNEL);
+	if (!ptr) {
+		pr_err("Allocation failed\n");
+		return;
+	}
+
+	phys = virt_to_phys(ptr);
+	kfree(phys_to_virt(phys));
+}
+
 static noinline void __init kmem_cache_oob(void)
 {
 	char *p;
@@ -737,6 +776,8 @@ static int __init kmalloc_tests_init(void)
 	kmalloc_uaf();
 	kmalloc_uaf_memset();
 	kmalloc_uaf2();
+	kfree_via_page();
+	kfree_via_phys();
 	kmem_cache_oob();
 	memcg_accounted_kmem_cache();
 	kasan_stack_oob();