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.

This patch makes __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.

This patch allows enabling CONFIG_KASAN_VMALLOC with HW_TAGS
and adjusts CONFIG_KASAN_VMALLOC description:

- Mention HW_TAGS support.
- Remove unneeded internal details: they have no place in Kconfig
  description and are already explained in the documentation.

Signed-off-by: Andrey Konovalov <redacted>
Co-developed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

---

Changes v1->v2:
- Allow enabling CONFIG_KASAN_VMALLOC with HW_TAGS in this patch.
- Move memory init for page_alloc pages backing vmalloc() into
  kasan_unpoison_vmalloc().
---
 include/linux/kasan.h | 30 +++++++++++++--
 lib/Kconfig.kasan     | 20 +++++-----
 mm/kasan/hw_tags.c    | 89 +++++++++++++++++++++++++++++++++++++++++++
 mm/kasan/shadow.c     | 11 +++++-
 mm/vmalloc.c          | 32 +++++++++++++---
 5 files changed, 162 insertions(+), 20 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 6a2619759e93..0bdc2b824b9c 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h

@@ -417,19 +417,40 @@ static inline void kasan_init_hw_tags(void) { }
 
 #ifdef CONFIG_KASAN_VMALLOC
 
+#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
+
 void kasan_populate_early_vm_area_shadow(void *start, unsigned long size);
 int kasan_populate_vmalloc(unsigned long addr, unsigned long size);
 void kasan_release_vmalloc(unsigned long start, unsigned long end,
 			   unsigned long free_region_start,
 			   unsigned long free_region_end);
 
+#else /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
+
+static inline void kasan_populate_early_vm_area_shadow(void *start,
+						       unsigned long size)
+{ }
+static inline int kasan_populate_vmalloc(unsigned long start,
+					unsigned long size)
+{
+	return 0;
+}
+static inline void kasan_release_vmalloc(unsigned long start,
+					 unsigned long end,
+					 unsigned long free_region_start,
+					 unsigned long free_region_end) { }
+
+#endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
+
 void * __must_check __kasan_unpoison_vmalloc(const void *start,
-					     unsigned long size);
+					     unsigned long size,
+					     bool vm_alloc, bool init);
 static __always_inline void * __must_check kasan_unpoison_vmalloc(
-					const void *start, unsigned long size)
+					const void *start, unsigned long size,
+					bool vm_alloc, bool init)