Commit 6c2f761d authored by Andrey Konovalov's avatar Andrey Konovalov Committed by Andrew Morton
Browse files

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: 23689e91 ("kasan, vmalloc: add vmalloc tagging for HW_TAGS")
Signed-off-by: default avatarAndrey 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent d9da8f6c

mm/kasan/hw_tags.c

+23 −9
Original line number Diff line number Diff line
@@ -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);

mm/vmalloc.c

+5 −5
Original line number Diff line number Diff line
@@ -3161,15 +3161,15 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align, 


	/*

	 * 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);