kasan: fix zeroing vmalloc memory with HW_TAGS

HW_TAGS KASAN skips zeroing page_alloc allocations backing vmalloc
mappings via __GFP_SKIP_ZERO.  Instead, these pages are zeroed via
kasan_unpoison_vmalloc() by passing the KASAN_VMALLOC_INIT flag.

The problem is that __kasan_unpoison_vmalloc() does not zero pages when
either kasan_vmalloc_enabled() or is_vmalloc_or_module_addr() fail.

Thus:

1. Change __vmalloc_node_range() to only set KASAN_VMALLOC_INIT when
   __GFP_SKIP_ZERO is set.

2. Change __kasan_unpoison_vmalloc() to always zero pages when the
   KASAN_VMALLOC_INIT flag is set.

3. Add WARN_ON() asserts to check that KASAN_VMALLOC_INIT cannot be set
   in other early return paths of __kasan_unpoison_vmalloc().

Also clean up the comment in __kasan_unpoison_vmalloc.

Link: https://lkml.kernel.org/r/4bc503537efdc539ffc3f461c1b70162eea31cf6.1654798516.git.andreyknvl@google.com
Fixes: 23689e91fb22 ("kasan, vmalloc: add vmalloc tagging for HW_TAGS")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 23 insertions, 9 deletions

diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 9e1b6544bfa8..9ad8eff71b28 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -257,27 +257,37 @@ static void unpoison_vmalloc_pages(const void *addr, u8 tag)
 	}
 }
 
+static void init_vmalloc_pages(const void *start, unsigned long size)
+{
+	const void *addr;
+
+	for (addr = start; addr < start + size; addr += PAGE_SIZE) {
+		struct page *page = virt_to_page(addr);
+
+		clear_highpage_kasan_tagged(page);
+	}
+}
+
 void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
 				kasan_vmalloc_flags_t flags)
 {
 	u8 tag;
 	unsigned long redzone_start, redzone_size;
 
-	if (!kasan_vmalloc_enabled())
-		return (void *)start;
-
-	if (!is_vmalloc_or_module_addr(start))
+	if (!kasan_vmalloc_enabled() || !is_vmalloc_or_module_addr(start)) {
+		if (flags & KASAN_VMALLOC_INIT)
+			init_vmalloc_pages(start, size);
 		return (void *)start;
+	}
 
 	/*
-	 * Skip unpoisoning and assigning a pointer tag for non-VM_ALLOC
-	 * mappings as:
+	 * Don't tag non-VM_ALLOC mappings, as:
 	 *
 	 * 1. Unlike the software KASAN modes, hardware tag-based KASAN only
 	 *    supports tagging physical memory. Therefore, it can only tag a
 	 *    single mapping of normal physical pages.
 	 * 2. Hardware tag-based KASAN can only tag memory mapped with special
-	 *    mapping protection bits, see arch_vmalloc_pgprot_modify().
+	 *    mapping protection bits, see arch_vmap_pgprot_tagged().
 	 *    As non-VM_ALLOC mappings can be mapped outside of vmalloc code,
 	 *    providing these bits would require tracking all non-VM_ALLOC
 	 *    mappers.
@@ -289,15 +299,19 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
 	 *
 	 * For non-VM_ALLOC allocations, page_alloc memory is tagged as usual.
 	 */
-	if (!(flags & KASAN_VMALLOC_VM_ALLOC))
+	if (!(flags & KASAN_VMALLOC_VM_ALLOC)) {
+		WARN_ON(flags & KASAN_VMALLOC_INIT);
 		return (void *)start;
+	}
 
 	/*
 	 * Don't tag executable memory.
 	 * The kernel doesn't tolerate having the PC register tagged.
 	 */
-	if (!(flags & KASAN_VMALLOC_PROT_NORMAL))
+	if (!(flags & KASAN_VMALLOC_PROT_NORMAL)) {
+		WARN_ON(flags & KASAN_VMALLOC_INIT);
 		return (void *)start;
+	}
 
 	tag = kasan_random_tag();
 	start = set_tag(start, tag);