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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: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220110231530.665970-2-willy@infradead.org
This commit is contained in:
Matthew Wilcox (Oracle) 2022-01-10 23:15:27 +00:00 committed by Kees Cook
parent a19944809f
commit 4e140f59d2
3 changed files with 21 additions and 6 deletions
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1
arch/x86/include/asm/highmem.h
View File

@ -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;

10
include/linux/highmem-internal.h
View File

@ -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 */
/*

16
mm/usercopy.c
View File

@ -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. */