Commit 23689e91 authored by Andrey Konovalov's avatar Andrey Konovalov Committed by Linus Torvalds
Browse files

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: default avatarAndrey Konovalov <andreyknvl@google.com>
Co-developed-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Acked-by: default avatarMarco 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 9353ffa6

include/linux/kasan.h

+32 −4
Original line number Diff line number Diff line
@@ -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);

static __always_inline void *kasan_unpoison_vmalloc(const void *start,

#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,

						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;

}

kernel/scs.c

+2 −2
Original line number Diff line number Diff line
@@ -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);

}

mm/kasan/hw_tags.c

+92 −0
Original line number Diff line number Diff line
@@ -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)

mm/kasan/shadow.c

+9 −1
Original line number Diff line number Diff line
@@ -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;

mm/vmalloc.c

+40 −11
Original line number Diff line number Diff line
@@ -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 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align, 
		goto fail;

	}



	/* Prepare arguments for __vmalloc_area_node(). */

	if (kasan_hw_tags_enabled() &&

	    pgprot_val(prot) == pgprot_val(PAGE_KERNEL)) {

		/*

		 * Modify protection bits to allow tagging.

	 * This must be done before mapping by __vmalloc_area_node().

		 * This must be done before mapping in __vmalloc_area_node().

		 */

	if (kasan_hw_tags_enabled() &&

	    pgprot_val(prot) == pgprot_val(PAGE_KERNEL))

		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 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets, 
	/*

	 * 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;