[PATCH 20/31] kasan, vmalloc: reset tags in vmalloc functions

[andrey.konovalov at linux.dev]

From: Andrey Konovalov <andreyknvl at google.com>

In preparation for adding vmalloc support to SW/HW_TAGS KASAN,
reset pointer tags in functions that use pointer values in
range checks.

vread() is a special case here. Resetting the pointer tag in its
prologue could technically lead to missing bad accesses to virtual
mappings in its implementation. However, vread() doesn't access the
virtual mappings cirectly. Instead, it recovers the physical address
via page_address(vmalloc_to_page()) and acceses that. And as
page_address() recovers the pointer tag, the accesses are checked.

Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
---
 mm/vmalloc.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index c5235e3e5857..a059b3100c0a 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -72,7 +72,7 @@ static const bool vmap_allow_huge = false;
 
 bool is_vmalloc_addr(const void *x)
 {
-	unsigned long addr = (unsigned long)x;
+	unsigned long addr = (unsigned long)kasan_reset_tag(x);
 
 	return addr >= VMALLOC_START && addr < VMALLOC_END;
 }
@@ -630,7 +630,7 @@ int is_vmalloc_or_module_addr(const void *x)
 	 * just put it in the vmalloc space.
 	 */
 #if defined(CONFIG_MODULES) && defined(MODULES_VADDR)
-	unsigned long addr = (unsigned long)x;
+	unsigned long addr = (unsigned long)kasan_reset_tag(x);
 	if (addr >= MODULES_VADDR && addr < MODULES_END)
 		return 1;
 #endif
@@ -804,6 +804,8 @@ static struct vmap_area *find_vmap_area_exceed_addr(unsigned long addr)
 	struct vmap_area *va = NULL;
 	struct rb_node *n = vmap_area_root.rb_node;
 
+	addr = (unsigned long)kasan_reset_tag((void *)addr);
+
 	while (n) {
 		struct vmap_area *tmp;
 
@@ -825,6 +827,8 @@ static struct vmap_area *__find_vmap_area(unsigned long addr)
 {
 	struct rb_node *n = vmap_area_root.rb_node;
 
+	addr = (unsigned long)kasan_reset_tag((void *)addr);
+
 	while (n) {
 		struct vmap_area *va;
 
@@ -2143,7 +2147,7 @@ EXPORT_SYMBOL_GPL(vm_unmap_aliases);
 void vm_unmap_ram(const void *mem, unsigned int count)
 {
 	unsigned long size = (unsigned long)count << PAGE_SHIFT;
-	unsigned long addr = (unsigned long)mem;
+	unsigned long addr = (unsigned long)kasan_reset_tag(mem);
 	struct vmap_area *va;
 
 	might_sleep();
@@ -3361,6 +3365,8 @@ long vread(char *buf, char *addr, unsigned long count)
 	unsigned long buflen = count;
 	unsigned long n;
 
+	addr = kasan_reset_tag(addr);
+
 	/* Don't allow overflow */
 	if ((unsigned long) addr + count < count)
 		count = -(unsigned long) addr;
-- 
2.25.1