Commit f6e39794 authored by Andrey Konovalov's avatar Andrey Konovalov Committed by Linus Torvalds
Browse files

kasan, vmalloc: only tag normal vmalloc allocations 

The kernel can use to allocate executable memory.  The only supported
way to do that is via __vmalloc_node_range() with the executable bit set
in the prot argument.  (vmap() resets the bit via pgprot_nx()).

Once tag-based KASAN modes start tagging vmalloc allocations, executing
code from such allocations will lead to the PC register getting a tag,
which is not tolerated by the kernel.

Only tag the allocations for normal kernel pages.

[andreyknvl@google.com: pass KASAN_VMALLOC_PROT_NORMAL to kasan_unpoison_vmalloc()]
  Link: https://lkml.kernel.org/r/9230ca3d3e40ffca041c133a524191fd71969a8d.1646233925.git.andreyknvl@google.com
[andreyknvl@google.com: support tagged vmalloc mappings]
  Link: https://lkml.kernel.org/r/2f6605e3a358cf64d73a05710cb3da356886ad29.1646233925.git.andreyknvl@google.com
[andreyknvl@google.com: don't unintentionally disabled poisoning]
  Link: https://lkml.kernel.org/r/de4587d6a719232e83c760113e46ed2d4d8da61e.1646757322.git.andreyknvl@google.com

Link: https://lkml.kernel.org/r/fbfd9939a4dc375923c9a5c6b9e7ab05c26b8c6b.1643047180.git.andreyknvl@google.com


Signed-off-by: default avatarAndrey Konovalov <andreyknvl@google.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: Vincenzo Frascino <vincenzo.frascino@arm.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 23689e91

include/linux/kasan.h

+4 −3
Original line number Diff line number Diff line
@@ -31,6 +31,7 @@ typedef unsigned int __bitwise kasan_vmalloc_flags_t; 
#define KASAN_VMALLOC_NONE		0x00u

#define KASAN_VMALLOC_INIT		0x01u

#define KASAN_VMALLOC_VM_ALLOC		0x02u

#define KASAN_VMALLOC_PROT_NORMAL	0x04u



#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)

kernel/scs.c

+8 −4
Original line number Diff line number Diff line
@@ -32,15 +32,19 @@ 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_VMALLOC_NONE);

			s = kasan_unpoison_vmalloc(s, SCS_SIZE,

						   KASAN_VMALLOC_PROT_NORMAL);

			memset(s, 0, SCS_SIZE);

			return s;

			goto out;

		}

	}



	return __vmalloc_node_range(SCS_SIZE, 1, VMALLOC_START, VMALLOC_END,

	s = __vmalloc_node_range(SCS_SIZE, 1, VMALLOC_START, VMALLOC_END,

				    GFP_SCS, PAGE_KERNEL, 0, node,

				    __builtin_return_address(0));



out:

	return kasan_reset_tag(s);

}



void *scs_alloc(int node)
@@ -78,7 +82,7 @@ void scs_free(void *s) 
		if (this_cpu_cmpxchg(scs_cache[i], 0, s) == NULL)

			return;



	kasan_unpoison_vmalloc(s, SCS_SIZE, KASAN_VMALLOC_NONE);

	kasan_unpoison_vmalloc(s, SCS_SIZE, KASAN_VMALLOC_PROT_NORMAL);

	vfree_atomic(s);

}

mm/kasan/hw_tags.c

+7 −0
Original line number Diff line number Diff line
@@ -247,6 +247,13 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size, 
	if (!(flags & KASAN_VMALLOC_VM_ALLOC))

		return (void *)start;



	/*

	 * Don't tag executable memory.

	 * The kernel doesn't tolerate having the PC register tagged.

	 */

	if (!(flags & KASAN_VMALLOC_PROT_NORMAL))

		return (void *)start;



	tag = kasan_random_tag();

	start = set_tag(start, tag);

mm/kasan/shadow.c

+8 −0
Original line number Diff line number Diff line
@@ -488,6 +488,14 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size, 
	if (!is_vmalloc_or_module_addr(start))

		return (void *)start;



	/*

	 * Don't tag executable memory with the tag-based mode.

	 * The kernel doesn't tolerate having the PC register tagged.

	 */

	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) &&

	    !(flags & KASAN_VMALLOC_PROT_NORMAL))

		return (void *)start;



	start = set_tag(start, kasan_random_tag());

	kasan_unpoison(start, size, false);

	return (void *)start;

mm/vmalloc.c

+29 −20
Original line number Diff line number Diff line
@@ -2242,7 +2242,7 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node) 
	 * 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);

	mem = kasan_unpoison_vmalloc(mem, size, KASAN_VMALLOC_PROT_NORMAL);



	return mem;

}
@@ -2481,7 +2481,7 @@ static struct vm_struct *__get_vm_area_node(unsigned long size, 
	 */

	if (!(flags & VM_ALLOC))

		area->addr = kasan_unpoison_vmalloc(area->addr, requested_size,

							KASAN_VMALLOC_NONE);

						    KASAN_VMALLOC_PROT_NORMAL);



	return area;

}
@@ -3091,7 +3091,7 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align, 
{

	struct vm_struct *area;

	void *ret;

	kasan_vmalloc_flags_t kasan_flags;

	kasan_vmalloc_flags_t kasan_flags = KASAN_VMALLOC_NONE;

	unsigned long real_size = size;

	unsigned long real_align = align;

	unsigned int shift = PAGE_SHIFT;
@@ -3144,23 +3144,30 @@ 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)) {

	/*

	 * Prepare arguments for __vmalloc_area_node() and

	 * kasan_unpoison_vmalloc().

	 */

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

		if (kasan_hw_tags_enabled()) {

			/*

			 * Modify protection bits to allow tagging.

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

			 * This must be done before mapping.

			 */

			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().

			 * 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;

		}



		/* Take note that the mapping is PAGE_KERNEL. */

		kasan_flags |= KASAN_VMALLOC_PROT_NORMAL;

	}



	/* Allocate physical pages and map them into vmalloc space. */

	ret = __vmalloc_area_node(area, gfp_mask, prot, shift, node);

	if (!ret)
@@ -3172,10 +3179,13 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align, 
	 * (except for the should_skip_init() check) to make sure that memory

	 * is initialized under the same conditions regardless of the enabled

	 * KASAN mode.

	 * Tag-based KASAN modes only assign tags to normal non-executable

	 * allocations, see __kasan_unpoison_vmalloc().

	 */

	kasan_flags = KASAN_VMALLOC_VM_ALLOC;

	kasan_flags |= KASAN_VMALLOC_VM_ALLOC;

	if (!want_init_on_free() && want_init_on_alloc(gfp_mask))

		kasan_flags |= KASAN_VMALLOC_INIT;

	/* KASAN_VMALLOC_PROT_NORMAL already set if required. */

	area->addr = kasan_unpoison_vmalloc(area->addr, real_size, kasan_flags);



	/*
@@ -3881,8 +3891,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets, 
	 */

	for (area = 0; area < nr_vms; area++)

		vms[area]->addr = kasan_unpoison_vmalloc(vms[area]->addr,

							 vms[area]->size,

							 KASAN_VMALLOC_NONE);

				vms[area]->size, KASAN_VMALLOC_PROT_NORMAL);



	kfree(vas);

	return vms;