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Commit 8e1f74ea authored by Kees Cook's avatar Kees Cook
Browse files

usercopy: remove page-spanning test for now 

A custom allocator without __GFP_COMP that copies to userspace has been
found in vmw_execbuf_process[1], so this disables the page-span checker
by placing it behind a CONFIG for future work where such things can be
tracked down later.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1373326



Reported-by: default avatarVinson Lee <vlee@freedesktop.org>
Fixes: f5509cc1 ("mm: Hardened usercopy")
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent a85d6b82

mm/usercopy.c

+35 −26
Original line number Diff line number Diff line
@@ -134,30 +134,15 @@ static inline const char *check_bogus_address(const void *ptr, unsigned long n) 
	return NULL;

}



static inline const char *check_heap_object(const void *ptr, unsigned long n,

					    bool to_user)

/* Checks for allocs that are marked in some way as spanning multiple pages. */

static inline const char *check_page_span(const void *ptr, unsigned long n,

					  struct page *page, bool to_user)

{

	struct page *page, *endpage;

#ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN

	const void *end = ptr + n - 1;

	struct page *endpage;

	bool is_reserved, is_cma;



	/*

	 * Some architectures (arm64) return true for virt_addr_valid() on

	 * vmalloced addresses. Work around this by checking for vmalloc

	 * first.

	 */

	if (is_vmalloc_addr(ptr))

		return NULL;



	if (!virt_addr_valid(ptr))

		return NULL;



	page = virt_to_head_page(ptr);



	/* Check slab allocator for flags and size. */

	if (PageSlab(page))

		return __check_heap_object(ptr, n, page);



	/*

	 * Sometimes the kernel data regions are not marked Reserved (see

	 * check below). And sometimes [_sdata,_edata) does not cover
@@ -186,7 +171,7 @@ static inline const char *check_heap_object(const void *ptr, unsigned long n, 
		   ((unsigned long)end & (unsigned long)PAGE_MASK)))

		return NULL;



	/* Allow if start and end are inside the same compound page. */

	/* Allow if fully inside the same compound (__GFP_COMP) page. */

	endpage = virt_to_head_page(end);

	if (likely(endpage == page))

		return NULL;
@@ -199,20 +184,44 @@ static inline const char *check_heap_object(const void *ptr, unsigned long n, 
	is_reserved = PageReserved(page);

	is_cma = is_migrate_cma_page(page);

	if (!is_reserved && !is_cma)

		goto reject;

		return "<spans multiple pages>";



	for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {

		page = virt_to_head_page(ptr);

		if (is_reserved && !PageReserved(page))

			goto reject;

			return "<spans Reserved and non-Reserved pages>";

		if (is_cma && !is_migrate_cma_page(page))

			goto reject;

			return "<spans CMA and non-CMA pages>";

	}

#endif



	return NULL;

}



reject:

	return "<spans multiple pages>";

static inline const char *check_heap_object(const void *ptr, unsigned long n,

					    bool to_user)

{

	struct page *page;



	/*

	 * Some architectures (arm64) return true for virt_addr_valid() on

	 * vmalloced addresses. Work around this by checking for vmalloc

	 * first.

	 */

	if (is_vmalloc_addr(ptr))

		return NULL;



	if (!virt_addr_valid(ptr))

		return NULL;



	page = virt_to_head_page(ptr);



	/* Check slab allocator for flags and size. */

	if (PageSlab(page))

		return __check_heap_object(ptr, n, page);



	/* Verify object does not incorrectly span multiple pages. */

	return check_page_span(ptr, n, page, to_user);

}



/*

security/Kconfig

+11 −0
Original line number Diff line number Diff line
@@ -147,6 +147,17 @@ config HARDENED_USERCOPY 
	  or are part of the kernel text. This kills entire classes

	  of heap overflow exploits and similar kernel memory exposures.



config HARDENED_USERCOPY_PAGESPAN

	bool "Refuse to copy allocations that span multiple pages"

	depends on HARDENED_USERCOPY

	depends on !COMPILE_TEST

	help

	  When a multi-page allocation is done without __GFP_COMP,

	  hardened usercopy will reject attempts to copy it. There are,

	  however, several cases of this in the kernel that have not all

	  been removed. This config is intended to be used only while

	  trying to find such users.



source security/selinux/Kconfig

source security/smack/Kconfig

source security/tomoyo/Kconfig