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>

diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 9e1b6544bfa8e6263fc6a9db58d68b345692e591..9ad8eff71b28ddcc607441ad940ec0cb37889df8 100644 (file)
--- 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);

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5977b178694d202dce3b71d26c78c98c89911d15..37939f96d2f4921164fe49ebde2220a2c5649464 100644 (file)
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3161,15 +3161,15 @@ again:
 
        /*
         * Mark the pages as accessible, now that they are mapped.
-        * The init condition should match the one in post_alloc_hook()
-        * (except for the should_skip_init() check) to make sure that memory
-        * is initialized under the same conditions regardless of the enabled
-        * KASAN mode.
+        * The condition for setting KASAN_VMALLOC_INIT should complement the
+        * one in post_alloc_hook() with regards to the __GFP_SKIP_ZERO check
+        * to make sure that memory is initialized under the same conditions.
         * Tag-based KASAN modes only assign tags to normal non-executable
         * allocations, see __kasan_unpoison_vmalloc().
         */
        kasan_flags |= KASAN_VMALLOC_VM_ALLOC;
-       if (!want_init_on_free() && want_init_on_alloc(gfp_mask))
+       if (!want_init_on_free() && want_init_on_alloc(gfp_mask) &&
+           (gfp_mask & __GFP_SKIP_ZERO))
                kasan_flags |= KASAN_VMALLOC_INIT;
        /* KASAN_VMALLOC_PROT_NORMAL already set if required. */
        area->addr = kasan_unpoison_vmalloc(area->addr, real_size, kasan_flags);