From cd52858c73f9f7df859a08fb08496ca39b9b3d8d Mon Sep 17 00:00:00 2001
From: Nick Piggin <npiggin@suse.de>
Date: Tue, 6 Jan 2009 14:39:20 -0800
Subject: [PATCH] mm: vmalloc make lazy unmapping configurable
Lazy unmapping in the vmalloc code has now opened the possibility for use
after free bugs to go undetected. We can catch those by forcing an unmap
and flush (which is going to be slow, but that's what happens).
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
mm/vmalloc.c | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 78689cba178f0..c5db9a7264d98 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -434,6 +434,27 @@ static void unmap_vmap_area(struct vmap_area *va)
vunmap_page_range(va->va_start, va->va_end);
}
+static void vmap_debug_free_range(unsigned long start, unsigned long end)
+{
+ /*
+ * Unmap page tables and force a TLB flush immediately if
+ * CONFIG_DEBUG_PAGEALLOC is set. This catches use after free
+ * bugs similarly to those in linear kernel virtual address
+ * space after a page has been freed.
+ *
+ * All the lazy freeing logic is still retained, in order to
+ * minimise intrusiveness of this debugging feature.
+ *
+ * This is going to be *slow* (linear kernel virtual address
+ * debugging doesn't do a broadcast TLB flush so it is a lot
+ * faster).
+ */
+#ifdef CONFIG_DEBUG_PAGEALLOC
+ vunmap_page_range(start, end);
+ flush_tlb_kernel_range(start, end);
+#endif
+}
+
/*
* lazy_max_pages is the maximum amount of virtual address space we gather up
* before attempting to purge with a TLB flush.
@@ -914,6 +935,7 @@ void vm_unmap_ram(const void *mem, unsigned int count)
BUG_ON(addr & (PAGE_SIZE-1));
debug_check_no_locks_freed(mem, size);
+ vmap_debug_free_range(addr, addr+size);
if (likely(count <= VMAP_MAX_ALLOC))
vb_free(mem, size);
@@ -1130,6 +1152,8 @@ struct vm_struct *remove_vm_area(const void *addr)
if (va && va->flags & VM_VM_AREA) {
struct vm_struct *vm = va->private;
struct vm_struct *tmp, **p;
+
+ vmap_debug_free_range(va->va_start, va->va_end);
free_unmap_vmap_area(va);
vm->size -= PAGE_SIZE;
--
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