Commit 4e140f59 authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Kees Cook
Browse files

mm/usercopy: Check kmap addresses properly 



If you are copying to an address in the kmap region, you may not copy
across a page boundary, no matter what the size of the underlying
allocation.  You can't kmap() a slab page because slab pages always
come from low memory.

Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220110231530.665970-2-willy@infradead.org
parent a1994480

arch/x86/include/asm/highmem.h

+1 −0
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ 
#include <asm/tlbflush.h>

#include <asm/paravirt.h>

#include <asm/fixmap.h>

#include <asm/pgtable_areas.h>



/* declarations for highmem.c */

extern unsigned long highstart_pfn, highend_pfn;

include/linux/highmem-internal.h

+10 −0
Original line number Diff line number Diff line
@@ -149,6 +149,11 @@ static inline void totalhigh_pages_add(long count) 
	atomic_long_add(count, &_totalhigh_pages);

}



static inline bool is_kmap_addr(const void *x)

{

	unsigned long addr = (unsigned long)x;

	return addr >= PKMAP_ADDR(0) && addr < PKMAP_ADDR(LAST_PKMAP);

}

#else /* CONFIG_HIGHMEM */



static inline struct page *kmap_to_page(void *addr)
@@ -234,6 +239,11 @@ static inline void __kunmap_atomic(void *addr) 
static inline unsigned int nr_free_highpages(void) { return 0; }

static inline unsigned long totalhigh_pages(void) { return 0UL; }



static inline bool is_kmap_addr(const void *x)

{

	return false;

}



#endif /* CONFIG_HIGHMEM */



/*

mm/usercopy.c

+10 −6
Original line number Diff line number Diff line
@@ -229,12 +229,16 @@ static inline void check_heap_object(const void *ptr, unsigned long n, 
	if (!virt_addr_valid(ptr))

		return;



	/*

	 * When CONFIG_HIGHMEM=y, kmap_to_page() will give either the

	 * highmem page or fallback to virt_to_page(). The following

	 * is effectively a highmem-aware virt_to_slab().

	 */

	folio = page_folio(kmap_to_page((void *)ptr));

	if (is_kmap_addr(ptr)) {

		unsigned long page_end = (unsigned long)ptr | (PAGE_SIZE - 1);



		if ((unsigned long)ptr + n - 1 > page_end)

			usercopy_abort("kmap", NULL, to_user,

					offset_in_page(ptr), n);

		return;

	}



	folio = virt_to_folio(ptr);



	if (folio_test_slab(folio)) {

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