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[1/4] mm/usercopy: Check kmap addresses properly

Message ID 20220110231530.665970-2-willy@infradead.org (mailing list archive)
State New
Headers show
Series Assorted improvements to usercopy | expand

Commit Message

Matthew Wilcox (Oracle) Jan. 10, 2022, 11:15 p.m. UTC 
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>
---
 arch/x86/include/asm/highmem.h   |  1 +
 include/linux/highmem-internal.h | 10 ++++++++++
 mm/usercopy.c                    | 16 ++++++++++------
 3 files changed, 21 insertions(+), 6 deletions(-)

Comments

Andrew Morton May 10, 2022, 3:37 a.m. UTC | #1 
On Mon, 10 Jan 2022 23:15:27 +0000 "Matthew Wilcox (Oracle)" <willy@infradead.org> wrote:

> If you are copying to an address in the kmap region, you may not copy
> across a page boundary,

In the source, the destination or in both, and why may we not?

> no matter what the size of the underlying
> allocation.  You can't kmap() a slab page because slab pages always
> come from low memory.

Why not?  kmap() does

	if (!PageHighMem(page))
		addr = page_address(page);
	else
		addr = kmap_high(page);
Kees Cook May 10, 2022, 10:01 p.m. UTC | #2 
On Mon, May 09, 2022 at 08:37:42PM -0700, Andrew Morton wrote:
> On Mon, 10 Jan 2022 23:15:27 +0000 "Matthew Wilcox (Oracle)" <willy@infradead.org> wrote:
> 
> > If you are copying to an address in the kmap region, you may not copy
> > across a page boundary,
> 
> In the source, the destination or in both, and why may we not?

This depends on direction. For copying to userspace, the source (kmap).
For copying from userspace, the destination (kmap).

> > no matter what the size of the underlying
> > allocation.  You can't kmap() a slab page because slab pages always
> > come from low memory.

As in it'll be processed as a slab page instead of kmap by the usercopy
checks?
diff mbox series

Patch

diff --git a/arch/x86/include/asm/highmem.h b/arch/x86/include/asm/highmem.h
index 032e020853aa..731ee7cc40a5 100644
--- a/arch/x86/include/asm/highmem.h
+++ b/arch/x86/include/asm/highmem.h
@@ -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;
diff --git a/include/linux/highmem-internal.h b/include/linux/highmem-internal.h
index 0a0b2b09b1b8..01fb76d101b0 100644
--- a/include/linux/highmem-internal.h
+++ b/include/linux/highmem-internal.h
@@ -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 */
 
 /*
diff --git a/mm/usercopy.c b/mm/usercopy.c
index d0d268135d96..2d13bc3bd83b 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -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. */