kasan, vmalloc: add vmalloc tagging for HW_TAGS
authorAndrey Konovalov <andreyknvl@google.com>
Fri, 25 Mar 2022 01:11:32 +0000 (18:11 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 25 Mar 2022 02:06:48 +0000 (19:06 -0700)
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>
include/linux/kasan.h
kernel/scs.c
mm/kasan/hw_tags.c
mm/kasan/shadow.c
mm/vmalloc.c

index d3efb6cbd0f51619b08b2b88115b49f89556c5ac..65fc5285bb59c3732d0bd3e2eec7e0321755a261 100644 (file)
@@ -26,6 +26,12 @@ struct kunit_kasan_expectation {
 
 #endif
 
+typedef unsigned int __bitwise kasan_vmalloc_flags_t;
+
+#define KASAN_VMALLOC_NONE     0x00u
+#define KASAN_VMALLOC_INIT     0x01u
+#define KASAN_VMALLOC_VM_ALLOC 0x02u
+
 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
 
 #include <linux/pgtable.h>
@@ -397,18 +403,39 @@ 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);
 
-void *__kasan_unpoison_vmalloc(const void *start, unsigned long size);
+#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 *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
+                              kasan_vmalloc_flags_t flags);
 static __always_inline void *kasan_unpoison_vmalloc(const void *start,
-                                                   unsigned long size)
+                                               unsigned long size,
+                                               kasan_vmalloc_flags_t flags)
 {
        if (kasan_enabled())
-               return __kasan_unpoison_vmalloc(start, size);
+               return __kasan_unpoison_vmalloc(start, size, flags);
        return (void *)start;
 }
 
@@ -435,7 +462,8 @@ static inline void kasan_release_vmalloc(unsigned long start,
                                         unsigned long free_region_end) { }
 
 static inline void *kasan_unpoison_vmalloc(const void *start,
-                                          unsigned long size)
+                                          unsigned long size,
+                                          kasan_vmalloc_flags_t flags)
 {
        return (void *)start;
 }
index 579841be88646c531621e1a444afb7dd32839d68..b83bc9251f996ee3d5d109b7eebd0af041e1ae92 100644 (file)
@@ -32,7 +32,7 @@ static void *__scs_alloc(int node)
        for (i = 0; i < NR_CACHED_SCS; i++) {
                s = this_cpu_xchg(scs_cache[i], NULL);
                if (s) {
-                       kasan_unpoison_vmalloc(s, SCS_SIZE);
+                       kasan_unpoison_vmalloc(s, SCS_SIZE, KASAN_VMALLOC_NONE);
                        memset(s, 0, SCS_SIZE);
                        return s;
                }
@@ -78,7 +78,7 @@ void scs_free(void *s)
                if (this_cpu_cmpxchg(scs_cache[i], 0, s) == NULL)
                        return;
 
-       kasan_unpoison_vmalloc(s, SCS_SIZE);
+       kasan_unpoison_vmalloc(s, SCS_SIZE, KASAN_VMALLOC_NONE);
        vfree_atomic(s);
 }
 
index 76cf2b6229c799b53142153669edd4aaef5f35db..21104fd518727ca2e39c4c57336c202a34987a8e 100644 (file)
@@ -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)
index 5a866f6663fc039e25bb89dc0e8f3df4fb84d0c3..b958babc8feda345070fd9c4ec1289e217ecc79c 100644 (file)
@@ -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;
 
index 8da8501db942f38d834a09a3dbaf72766755bd9e..185ab3e27d1306773ed602afa73e0a0afda21f3f 100644 (file)
@@ -2237,8 +2237,12 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node)
                return NULL;
        }
 
-       /* Mark the pages as accessible, now that they are mapped. */
-       mem = kasan_unpoison_vmalloc(mem, size);
+       /*
+        * Mark the pages as accessible, now that they are mapped.
+        * With hardware tag-based KASAN, marking is skipped for
+        * non-VM_ALLOC mappings, see __kasan_unpoison_vmalloc().
+        */
+       mem = kasan_unpoison_vmalloc(mem, size, KASAN_VMALLOC_NONE);
 
        return mem;
 }
@@ -2472,9 +2476,12 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
         * best-effort approach, as they can be mapped outside of vmalloc code.
         * For VM_ALLOC mappings, the pages are marked as accessible after
         * getting mapped in __vmalloc_node_range().
+        * With hardware tag-based KASAN, marking is skipped for
+        * non-VM_ALLOC mappings, see __kasan_unpoison_vmalloc().
         */
        if (!(flags & VM_ALLOC))
-               area->addr = kasan_unpoison_vmalloc(area->addr, requested_size);
+               area->addr = kasan_unpoison_vmalloc(area->addr, requested_size,
+                                                       KASAN_VMALLOC_NONE);
 
        return area;
 }
@@ -3084,6 +3091,7 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 {
        struct vm_struct *area;
        void *ret;
+       kasan_vmalloc_flags_t kasan_flags;
        unsigned long real_size = size;
        unsigned long real_align = align;
        unsigned int shift = PAGE_SHIFT;
@@ -3136,21 +3144,39 @@ again:
                goto fail;
        }
 
-       /*
-        * Modify protection bits to allow tagging.
-        * This must be done before mapping by __vmalloc_area_node().
-        */
+       /* Prepare arguments for __vmalloc_area_node(). */
        if (kasan_hw_tags_enabled() &&
-           pgprot_val(prot) == pgprot_val(PAGE_KERNEL))
+           pgprot_val(prot) == pgprot_val(PAGE_KERNEL)) {
+               /*
+                * Modify protection bits to allow tagging.
+                * This must be done before mapping in __vmalloc_area_node().
+                */
                prot = arch_vmap_pgprot_tagged(prot);
 
+               /*
+                * Skip page_alloc poisoning and zeroing for physical pages
+                * backing VM_ALLOC mapping. Memory is instead poisoned and
+                * zeroed by kasan_unpoison_vmalloc().
+                */
+               gfp_mask |= __GFP_SKIP_KASAN_UNPOISON | __GFP_SKIP_ZERO;
+       }
+
        /* Allocate physical pages and map them into vmalloc space. */
        ret = __vmalloc_area_node(area, gfp_mask, prot, shift, node);
        if (!ret)
                goto fail;
 
-       /* Mark the pages as accessible, now that they are mapped. */
-       area->addr = kasan_unpoison_vmalloc(area->addr, real_size);
+       /*
+        * 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.
+        */
+       kasan_flags = KASAN_VMALLOC_VM_ALLOC;
+       if (!want_init_on_free() && want_init_on_alloc(gfp_mask))
+               kasan_flags |= KASAN_VMALLOC_INIT;
+       area->addr = kasan_unpoison_vmalloc(area->addr, real_size, kasan_flags);
 
        /*
         * In this function, newly allocated vm_struct has VM_UNINITIALIZED
@@ -3850,10 +3876,13 @@ retry:
        /*
         * Mark allocated areas as accessible. Do it now as a best-effort
         * approach, as they can be mapped outside of vmalloc code.
+        * With hardware tag-based KASAN, marking is skipped for
+        * non-VM_ALLOC mappings, see __kasan_unpoison_vmalloc().
         */
        for (area = 0; area < nr_vms; area++)
                vms[area]->addr = kasan_unpoison_vmalloc(vms[area]->addr,
-                                                        vms[area]->size);
+                                                        vms[area]->size,
+                                                        KASAN_VMALLOC_NONE);
 
        kfree(vas);
        return vms;