ARM: add support to dump the kernel page tables

This patch allows the kernel page tables to be dumped via a debugfs file,
allowing kernel developers to check the layout of the kernel page tables
and the verify the various permissions and type settings.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/Kconfig.debug

@@ -2,6 +2,18 @@ menu "Kernel hacking"
 
 source "lib/Kconfig.debug"
 
+config ARM_PTDUMP
+	bool "Export kernel pagetable layout to userspace via debugfs"
+	depends on DEBUG_KERNEL
+	select DEBUG_FS
+	---help---
+	  Say Y here if you want to show the kernel pagetable layout in a
+	  debugfs file. This information is only useful for kernel developers
+	  who are working in architecture specific areas of the kernel.
+	  It is probably not a good idea to enable this feature in a production
+	  kernel.
+	  If in doubt, say "N"
+
 config STRICT_DEVMEM
 	bool "Filter access to /dev/mem"
 	depends on MMU

arch/arm/include/asm/pgtable-2level.h

@@ -160,6 +160,7 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
 	return (pmd_t *)pud;
 }
 
+#define pmd_large(pmd)		(pmd_val(pmd) & 2)
 #define pmd_bad(pmd)		(pmd_val(pmd) & 2)
 
 #define copy_pmd(pmdpd,pmdps)		\

arch/arm/include/asm/pgtable-3level.h

@@ -142,6 +142,7 @@
 						 PMD_TYPE_TABLE)
 #define pmd_sect(pmd)		((pmd_val(pmd) & PMD_TYPE_MASK) == \
 						 PMD_TYPE_SECT)
+#define pmd_large(pmd)		pmd_sect(pmd)
 
 #define pud_clear(pudp)			\
 	do {				\

arch/arm/mm/Makefile

@@ -12,6 +12,7 @@ ifneq ($(CONFIG_MMU),y)
 obj-y				+= nommu.o
 endif
 
+obj-$(CONFIG_ARM_PTDUMP)	+= dump.o
 obj-$(CONFIG_MODULES)		+= proc-syms.o
 
 obj-$(CONFIG_ALIGNMENT_TRAP)	+= alignment.o

arch/arm/mm/dump.c

+/*
+ * Debug helper to dump the current kernel pagetables of the system
+ * so that we can see what the various memory ranges are set to.
+ *
+ * Derived from x86 implementation:
+ * (C) Copyright 2008 Intel Corporation
+ *
+ * Author: Arjan van de Ven <arjan@linux.intel.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; version 2
+ * of the License.
+ */
+#include <linux/debugfs.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/seq_file.h>
+
+#include <asm/fixmap.h>
+#include <asm/pgtable.h>
+
+struct addr_marker {
+	unsigned long start_address;
+	const char *name;
+};
+
+static struct addr_marker address_markers[] = {
+	{ MODULES_VADDR,	"Modules" },
+	{ PAGE_OFFSET,		"Kernel Mapping" },
+	{ 0,			"vmalloc() Area" },
+	{ VMALLOC_END,		"vmalloc() End" },
+	{ FIXADDR_START,	"Fixmap Area" },
+	{ CONFIG_VECTORS_BASE,	"Vectors" },
+	{ CONFIG_VECTORS_BASE + PAGE_SIZE * 2, "Vectors End" },
+	{ -1,			NULL },
+};
+
+struct pg_state {
+	struct seq_file *seq;
+	const struct addr_marker *marker;
+	unsigned long start_address;
+	unsigned level;
+	u64 current_prot;
+};
+
+struct prot_bits {
+	u64		mask;
+	u64		val;
+	const char	*set;
+	const char	*clear;
+};
+
+static const struct prot_bits pte_bits[] = {
+	{
+		.mask	= L_PTE_USER,
+		.val	= L_PTE_USER,
+		.set	= "USR",
+		.clear	= "   ",
+	}, {
+		.mask	= L_PTE_RDONLY,
+		.val	= L_PTE_RDONLY,
+		.set	= "ro",
+		.clear	= "RW",
+	}, {
+		.mask	= L_PTE_XN,
+		.val	= L_PTE_XN,
+		.set	= "NX",
+		.clear	= "x ",
+	}, {
+		.mask	= L_PTE_SHARED,
+		.val	= L_PTE_SHARED,
+		.set	= "SHD",
+		.clear	= "   ",
+	}, {
+		.mask	= L_PTE_MT_MASK,
+		.val	= L_PTE_MT_UNCACHED,
+		.set	= "SO/UNCACHED",
+	}, {
+		.mask	= L_PTE_MT_MASK,
+		.val	= L_PTE_MT_BUFFERABLE,
+		.set	= "MEM/BUFFERABLE/WC",
+	}, {
+		.mask	= L_PTE_MT_MASK,
+		.val	= L_PTE_MT_WRITETHROUGH,
+		.set	= "MEM/CACHED/WT",
+	}, {
+		.mask	= L_PTE_MT_MASK,
+		.val	= L_PTE_MT_WRITEBACK,
+		.set	= "MEM/CACHED/WBRA",
+#ifndef CONFIG_ARM_LPAE
+	}, {
+		.mask	= L_PTE_MT_MASK,
+		.val	= L_PTE_MT_MINICACHE,
+		.set	= "MEM/MINICACHE",
+#endif
+	}, {
+		.mask	= L_PTE_MT_MASK,
+		.val	= L_PTE_MT_WRITEALLOC,
+		.set	= "MEM/CACHED/WBWA",
+	}, {
+		.mask	= L_PTE_MT_MASK,
+		.val	= L_PTE_MT_DEV_SHARED,
+		.set	= "DEV/SHARED",
+#ifndef CONFIG_ARM_LPAE
+	}, {
+		.mask	= L_PTE_MT_MASK,
+		.val	= L_PTE_MT_DEV_NONSHARED,
+		.set	= "DEV/NONSHARED",
+#endif
+	}, {
+		.mask	= L_PTE_MT_MASK,
+		.val	= L_PTE_MT_DEV_WC,
+		.set	= "DEV/WC",
+	}, {
+		.mask	= L_PTE_MT_MASK,
+		.val	= L_PTE_MT_DEV_CACHED,
+		.set	= "DEV/CACHED",
+	},
+};
+
+static const struct prot_bits section_bits[] = {
+#ifndef CONFIG_ARM_LPAE
+	/* These are approximate */
+	{
+		.mask	= PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
+		.val	= 0,
+		.set	= "    ro",
+	}, {
+		.mask	= PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
+		.val	= PMD_SECT_AP_WRITE,
+		.set	= "    RW",
+	}, {
+		.mask	= PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
+		.val	= PMD_SECT_AP_READ,
+		.set	= "USR ro",
+	}, {
+		.mask	= PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
+		.val	= PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
+		.set	= "USR RW",
+#else
+	{
+		.mask	= PMD_SECT_USER,
+		.val	= PMD_SECT_USER,
+		.set	= "USR",
+	}, {
+		.mask	= PMD_SECT_RDONLY,
+		.val	= PMD_SECT_RDONLY,
+		.set	= "ro",
+		.clear	= "RW",
+#endif
+	}, {
+		.mask	= PMD_SECT_XN,
+		.val	= PMD_SECT_XN,
+		.set	= "NX",
+		.clear	= "x ",
+	}, {
+		.mask	= PMD_SECT_S,
+		.val	= PMD_SECT_S,
+		.set	= "SHD",
+		.clear	= "   ",
+	},
+};
+
+struct pg_level {
+	const struct prot_bits *bits;
+	size_t num;
+	u64 mask;
+};
+
+static struct pg_level pg_level[] = {
+	{
+	}, { /* pgd */
+	}, { /* pud */
+	}, { /* pmd */
+		.bits	= section_bits,
+		.num	= ARRAY_SIZE(section_bits),
+	}, { /* pte */
+		.bits	= pte_bits,
+		.num	= ARRAY_SIZE(pte_bits),
+	},
+};
+
+static void dump_prot(struct pg_state *st, const struct prot_bits *bits, size_t num)
+{
+	unsigned i;
+
+	for (i = 0; i < num; i++, bits++) {
+		const char *s;
+
+		if ((st->current_prot & bits->mask) == bits->val)
+			s = bits->set;
+		else
+			s = bits->clear;
+
+		if (s)
+			seq_printf(st->seq, " %s", s);
+	}
+}
+
+static void note_page(struct pg_state *st, unsigned long addr, unsigned level, u64 val)
+{
+	static const char units[] = "KMGTPE";
+	u64 prot = val & pg_level[level].mask;
+
+	if (addr < USER_PGTABLES_CEILING)
+		return;
+
+	if (!st->level) {
+		st->level = level;
+		st->current_prot = prot;
+		seq_printf(st->seq, "---[ %s ]---\n", st->marker->name);
+	} else if (prot != st->current_prot || level != st->level ||
+		   addr >= st->marker[1].start_address) {
+		const char *unit = units;
+		unsigned long delta;
+
+		if (st->current_prot) {
+			seq_printf(st->seq, "0x%08lx-0x%08lx   ",
+				   st->start_address, addr);
+
+			delta = (addr - st->start_address) >> 10;
+			while (!(delta & 1023) && unit[1]) {
+				delta >>= 10;
+				unit++;
+			}
+			seq_printf(st->seq, "%9lu%c", delta, *unit);
+			if (pg_level[st->level].bits)
+				dump_prot(st, pg_level[st->level].bits, pg_level[st->level].num);
+			seq_printf(st->seq, "\n");
+		}
+
+		if (addr >= st->marker[1].start_address) {
+			st->marker++;
+			seq_printf(st->seq, "---[ %s ]---\n", st->marker->name);
+		}
+		st->start_address = addr;
+		st->current_prot = prot;
+		st->level = level;
+	}
+}
+
+static void walk_pte(struct pg_state *st, pmd_t *pmd, unsigned long start)
+{
+	pte_t *pte = pte_offset_kernel(pmd, 0);
+	unsigned long addr;
+	unsigned i;
+
+	for (i = 0; i < PTRS_PER_PTE; i++, pte++) {
+		addr = start + i * PAGE_SIZE;
+		note_page(st, addr, 4, pte_val(*pte));
+	}
+}
+
+static void walk_pmd(struct pg_state *st, pud_t *pud, unsigned long start)
+{
+	pmd_t *pmd = pmd_offset(pud, 0);
+	unsigned long addr;
+	unsigned i;
+
+	for (i = 0; i < PTRS_PER_PMD; i++, pmd++) {
+		addr = start + i * PMD_SIZE;
+		if (pmd_none(*pmd) || pmd_large(*pmd) || !pmd_present(*pmd))
+			note_page(st, addr, 3, pmd_val(*pmd));
+		else
+			walk_pte(st, pmd, addr);
+	}
+}
+
+static void walk_pud(struct pg_state *st, pgd_t *pgd, unsigned long start)
+{
+	pud_t *pud = pud_offset(pgd, 0);
+	unsigned long addr;
+	unsigned i;
+
+	for (i = 0; i < PTRS_PER_PUD; i++, pud++) {
+		addr = start + i * PUD_SIZE;
+		if (!pud_none(*pud)) {
+			walk_pmd(st, pud, addr);
+		} else {
+			note_page(st, addr, 2, pud_val(*pud));
+		}
+	}
+}
+
+static void walk_pgd(struct seq_file *m)
+{
+	pgd_t *pgd = swapper_pg_dir;
+	struct pg_state st;
+	unsigned long addr;
+	unsigned i, pgdoff = USER_PGTABLES_CEILING / PGDIR_SIZE;
+
+	memset(&st, 0, sizeof(st));
+	st.seq = m;
+	st.marker = address_markers;
+
+	pgd += pgdoff;
+
+	for (i = pgdoff; i < PTRS_PER_PGD; i++, pgd++) {
+		addr = i * PGDIR_SIZE;
+		if (!pgd_none(*pgd)) {
+			walk_pud(&st, pgd, addr);
+		} else {
+			note_page(&st, addr, 1, pgd_val(*pgd));
+		}
+	}
+
+	note_page(&st, 0, 0, 0);
+}
+
+static int ptdump_show(struct seq_file *m, void *v)
+{
+	walk_pgd(m);
+	return 0;
+}
+
+static int ptdump_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, ptdump_show, NULL);
+}
+
+static const struct file_operations ptdump_fops = {
+	.open		= ptdump_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static int ptdump_init(void)
+{
+	struct dentry *pe;
+	unsigned i, j;
+
+	for (i = 0; i < ARRAY_SIZE(pg_level); i++)
+		if (pg_level[i].bits)
+			for (j = 0; j < pg_level[i].num; j++)
+				pg_level[i].mask |= pg_level[i].bits[j].mask;
+
+	address_markers[2].start_address = VMALLOC_START;
+
+	pe = debugfs_create_file("kernel_page_tables", 0400, NULL, NULL,
+				 &ptdump_fops);
+	return pe ? 0 : -ENOMEM;
+}
+__initcall(ptdump_init);