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authorAndrey Konovalov <andreyknvl@google.com>2022-03-25 04:11:32 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2022-03-25 05:06:48 +0300
commit23689e91fb22c15b84ac6c22ad9942039792f3af (patch)
tree43d39324d73f7b154524c966a9d49ec552faf6d4 /mm
parent9353ffa6e9e90d2b6348209cf2b95a8ffee18711 (diff)
downloadlinux-23689e91fb22c15b84ac6c22ad9942039792f3af.tar.xz
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>
Diffstat (limited to 'mm')
-rw-r--r--mm/kasan/hw_tags.c92
-rw-r--r--mm/kasan/shadow.c10
-rw-r--r--mm/vmalloc.c51
3 files changed, 141 insertions, 12 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;
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 8da8501db942..185ab3e27d13 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -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;