kasan, vmalloc: add vmalloc tagging for HW_TAGS

Add vmalloc tagging support to HW_TAGS KASAN.

The key difference between HW_TAGS and the other two KASAN modes when it
comes to vmalloc: HW_TAGS KASAN can only assign tags to physical memory.
The other two modes have shadow memory covering every mapped virtual
memory region.

Make __kasan_unpoison_vmalloc() for HW_TAGS KASAN:

 - Skip non-VM_ALLOC mappings as HW_TAGS KASAN can only tag a single
   mapping of normal physical memory; see the comment in the function.

 - Generate a random tag, tag the returned pointer and the allocation,
   and initialize the allocation at the same time.

 - Propagate the tag into the page stucts to allow accesses through
   page_address(vmalloc_to_page()).

The rest of vmalloc-related KASAN hooks are not needed:

 - The shadow-related ones are fully skipped.

 - __kasan_poison_vmalloc() is kept as a no-op with a comment.

Poisoning and zeroing of physical pages that are backing vmalloc()
allocations are skipped via __GFP_SKIP_KASAN_UNPOISON and
__GFP_SKIP_ZERO: __kasan_unpoison_vmalloc() does that instead.

Enabling CONFIG_KASAN_VMALLOC with HW_TAGS is not yet allowed.

Link: https://lkml.kernel.org/r/d19b2e9e59a9abc59d05b72dea8429dcaea739c6.1643047180.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Co-developed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Acked-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 101 insertions, 1 deletions

diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 76cf2b6229c7..21104fd51872 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -192,6 +192,98 @@ void __init kasan_init_hw_tags(void)
 		kasan_stack_collection_enabled() ? "on" : "off");
 }
 
+#ifdef CONFIG_KASAN_VMALLOC
+
+static void unpoison_vmalloc_pages(const void *addr, u8 tag)
+{
+	struct vm_struct *area;
+	int i;
+
+	/*
+	 * As hardware tag-based KASAN only tags VM_ALLOC vmalloc allocations
+	 * (see the comment in __kasan_unpoison_vmalloc), all of the pages
+	 * should belong to a single area.
+	 */
+	area = find_vm_area((void *)addr);
+	if (WARN_ON(!area))
+		return;
+
+	for (i = 0; i < area->nr_pages; i++) {
+		struct page *page = area->pages[i];
+
+		page_kasan_tag_set(page, tag);
+	}
+}
+
+void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
+				kasan_vmalloc_flags_t flags)
+{
+	u8 tag;
+	unsigned long redzone_start, redzone_size;
+
+	if (!is_vmalloc_or_module_addr(start))
+		return (void *)start;
+
+	/*
+	 * Skip unpoisoning and assigning a pointer tag for 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().
+	 *    As non-VM_ALLOC mappings can be mapped outside of vmalloc code,
+	 *    providing these bits would require tracking all non-VM_ALLOC
+	 *    mappers.
+	 *
+	 * Thus, for VM_ALLOC mappings, hardware tag-based KASAN only tags
+	 * the first virtual mapping, which is created by vmalloc().
+	 * Tagging the page_alloc memory backing that vmalloc() allocation is
+	 * skipped, see ___GFP_SKIP_KASAN_UNPOISON.
+	 *
+	 * For non-VM_ALLOC allocations, page_alloc memory is tagged as usual.
+	 */
+	if (!(flags & KASAN_VMALLOC_VM_ALLOC))
+		return (void *)start;
+
+	tag = kasan_random_tag();
+	start = set_tag(start, tag);
+
+	/* Unpoison and initialize memory up to size. */
+	kasan_unpoison(start, size, flags & KASAN_VMALLOC_INIT);
+
+	/*
+	 * Explicitly poison and initialize the in-page vmalloc() redzone.
+	 * Unlike software KASAN modes, hardware tag-based KASAN doesn't
+	 * unpoison memory when populating shadow for vmalloc() space.
+	 */
+	redzone_start = round_up((unsigned long)start + size,
+				 KASAN_GRANULE_SIZE);
+	redzone_size = round_up(redzone_start, PAGE_SIZE) - redzone_start;
+	kasan_poison((void *)redzone_start, redzone_size, KASAN_TAG_INVALID,
+		     flags & KASAN_VMALLOC_INIT);
+
+	/*
+	 * Set per-page tag flags to allow accessing physical memory for the
+	 * vmalloc() mapping through page_address(vmalloc_to_page()).
+	 */
+	unpoison_vmalloc_pages(start, tag);
+
+	return (void *)start;
+}
+
+void __kasan_poison_vmalloc(const void *start, unsigned long size)
+{
+	/*
+	 * No tagging here.
+	 * The physical pages backing the vmalloc() allocation are poisoned
+	 * through the usual page_alloc paths.
+	 */
+}
+
+#endif
+
 #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
 
 void kasan_enable_tagging_sync(void)
diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
index 5a866f6663fc..b958babc8fed 100644
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -475,8 +475,16 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
 	}
 }
 
-void *__kasan_unpoison_vmalloc(const void *start, unsigned long size)
+void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
+			       kasan_vmalloc_flags_t flags)
 {
+	/*
+	 * Software KASAN modes unpoison both VM_ALLOC and non-VM_ALLOC
+	 * mappings, so the KASAN_VMALLOC_VM_ALLOC flag is ignored.
+	 * Software KASAN modes can't optimize zeroing memory by combining it
+	 * with setting memory tags, so the KASAN_VMALLOC_INIT flag is ignored.
+	 */
+
 	if (!is_vmalloc_or_module_addr(start))
 		return (void *)start;