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@@ -0,0 +1,135 @@
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+/*
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+ * This code is used on x86_64 to create page table identity mappings on
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+ * demand by building up a new set of page tables (or appending to the
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+ * existing ones), and then switching over to them when ready.
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+ */
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+
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+/*
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+ * Since we're dealing with identity mappings, physical and virtual
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+ * addresses are the same, so override these defines which are ultimately
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+ * used by the headers in misc.h.
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+ */
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+#define __pa(x) ((unsigned long)(x))
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+#define __va(x) ((void *)((unsigned long)(x)))
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+
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+#include "misc.h"
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+
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+/* These actually do the work of building the kernel identity maps. */
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+#include <asm/init.h>
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+#include <asm/pgtable.h>
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+#include "../../mm/ident_map.c"
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+
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+/* Used by pgtable.h asm code to force instruction serialization. */
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+unsigned long __force_order;
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+
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+/* Used to track our page table allocation area. */
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+struct alloc_pgt_data {
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+ unsigned char *pgt_buf;
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+ unsigned long pgt_buf_size;
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+ unsigned long pgt_buf_offset;
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+};
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+
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+/*
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+ * Allocates space for a page table entry, using struct alloc_pgt_data
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+ * above. Besides the local callers, this is used as the allocation
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+ * callback in mapping_info below.
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+ */
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+static void *alloc_pgt_page(void *context)
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+{
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+ struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context;
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+ unsigned char *entry;
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+
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+ /* Validate there is space available for a new page. */
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+ if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
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+ debug_putstr("out of pgt_buf in " __FILE__ "!?\n");
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+ debug_putaddr(pages->pgt_buf_offset);
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+ debug_putaddr(pages->pgt_buf_size);
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+ return NULL;
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+ }
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+
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+ entry = pages->pgt_buf + pages->pgt_buf_offset;
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+ pages->pgt_buf_offset += PAGE_SIZE;
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+
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+ return entry;
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+}
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+
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+/* Used to track our allocated page tables. */
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+static struct alloc_pgt_data pgt_data;
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+
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+/* The top level page table entry pointer. */
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+static unsigned long level4p;
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+
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+/* Locates and clears a region for a new top level page table. */
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+static void prepare_level4(void)
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+{
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+ /*
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+ * It should be impossible for this not to already be true,
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+ * but since calling this a second time would rewind the other
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+ * counters, let's just make sure this is reset too.
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+ */
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+ pgt_data.pgt_buf_offset = 0;
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+
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+ /*
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+ * If we came here via startup_32(), cr3 will be _pgtable already
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+ * and we must append to the existing area instead of entirely
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+ * overwriting it.
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+ */
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+ level4p = read_cr3();
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+ if (level4p == (unsigned long)_pgtable) {
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+ debug_putstr("booted via startup_32()\n");
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+ pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
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+ pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
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+ memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
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+ } else {
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+ debug_putstr("booted via startup_64()\n");
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+ pgt_data.pgt_buf = _pgtable;
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+ pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
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+ memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
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+ level4p = (unsigned long)alloc_pgt_page(&pgt_data);
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+ }
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+}
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+
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+/*
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+ * Mapping information structure passed to kernel_ident_mapping_init().
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+ * Since this never changes, there's no reason to repeatedly fill it
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+ * in on the stack when calling add_identity_map().
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+ */
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+static struct x86_mapping_info mapping_info = {
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+ .alloc_pgt_page = alloc_pgt_page,
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+ .context = &pgt_data,
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+ .pmd_flag = __PAGE_KERNEL_LARGE_EXEC,
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+};
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+
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+/*
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+ * Adds the specified range to what will become the new identity mappings.
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+ * Once all ranges have been added, the new mapping is activated by calling
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+ * finalize_identity_maps() below.
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+ */
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+void add_identity_map(unsigned long start, unsigned long size)
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+{
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+ unsigned long end = start + size;
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+
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+ /* Make sure we have a top level page table ready to use. */
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+ if (!level4p)
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+ prepare_level4();
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+
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+ /* Align boundary to 2M. */
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+ start = round_down(start, PMD_SIZE);
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+ end = round_up(end, PMD_SIZE);
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+ if (start >= end)
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+ return;
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+
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+ /* Build the mapping. */
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+ kernel_ident_mapping_init(&mapping_info, (pgd_t *)level4p,
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+ start, end);
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+}
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+
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+/*
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+ * This switches the page tables to the new level4 that has been built
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+ * via calls to add_identity_map() above. If booted via startup_32(),
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+ * this is effectively a no-op.
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+ */
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+void finalize_identity_maps(void)
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+{
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+ write_cr3(level4p);
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+}
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Kees Cook