[kernel-hardening][PATCH v3 1/3] arm: mm: dump: make page table dumping reusable

[kernel-hardening][PATCH v3 1/3] arm: mm: dump: make page table dumping reusable

[Jinbum Park]

This patch refactors the arm page table dumping code,
so multiple tables may be registered with the framework.

This patch refers below commits of arm64.
(4674fdb9f149 ("arm64: mm: dump: make page table dumping reusable"))
(4ddb9bf83349 ("arm64: dump: Make ptdump debugfs a separate option"))

Signed-off-by: Jinbum Park <jinb.park7@gmail.com>
---
v3: No changes

 arch/arm/Kconfig.debug        |  6 +++-
 arch/arm/include/asm/ptdump.h | 48 ++++++++++++++++++++++++++++++++
 arch/arm/mm/Makefile          |  3 +-
 arch/arm/mm/dump.c            | 65 +++++++++++++++++++------------------------
 arch/arm/mm/ptdump_debugfs.c  | 34 ++++++++++++++++++++++
 5 files changed, 117 insertions(+), 39 deletions(-)
 create mode 100644 arch/arm/include/asm/ptdump.h
 create mode 100644 arch/arm/mm/ptdump_debugfs.c

diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index 17685e1..e7b94db 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -3,10 +3,14 @@ menu "Kernel hacking"
 
 source "lib/Kconfig.debug"
 
-config ARM_PTDUMP
+config ARM_PTDUMP_CORE
+	def_bool n
+
+config ARM_PTDUMP_DEBUGFS
 	bool "Export kernel pagetable layout to userspace via debugfs"
 	depends on DEBUG_KERNEL
 	depends on MMU
+	select ARM_PTDUMP_CORE
 	select DEBUG_FS
 	---help---
 	  Say Y here if you want to show the kernel pagetable layout in a
diff --git a/arch/arm/include/asm/ptdump.h b/arch/arm/include/asm/ptdump.h
new file mode 100644
index 0000000..3a6c0b7
--- /dev/null
+++ b/arch/arm/include/asm/ptdump.h
@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2014 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef __ASM_PTDUMP_H
+#define __ASM_PTDUMP_H
+
+#ifdef CONFIG_ARM_PTDUMP_CORE
+
+#include <linux/mm_types.h>
+#include <linux/seq_file.h>
+
+struct addr_marker {
+	unsigned long start_address;
+	char *name;
+};
+
+struct ptdump_info {
+	struct mm_struct		*mm;
+	const struct addr_marker	*markers;
+	unsigned long			base_addr;
+};
+
+void ptdump_walk_pgd(struct seq_file *s, struct ptdump_info *info);
+#ifdef CONFIG_ARM_PTDUMP_DEBUGFS
+int ptdump_debugfs_register(struct ptdump_info *info, const char *name);
+#else
+static inline int ptdump_debugfs_register(struct ptdump_info *info,
+					const char *name)
+{
+	return 0;
+}
+#endif /* CONFIG_ARM_PTDUMP_DEBUGFS */
+
+#endif /* CONFIG_ARM_PTDUMP_CORE */
+
+#endif /* __ASM_PTDUMP_H */
diff --git a/arch/arm/mm/Makefile b/arch/arm/mm/Makefile
index 01bcc33..28be5f4 100644
--- a/arch/arm/mm/Makefile
+++ b/arch/arm/mm/Makefile
@@ -13,7 +13,8 @@ obj-y				+= nommu.o
 obj-$(CONFIG_ARM_MPU)		+= pmsa-v7.o
 endif
 
-obj-$(CONFIG_ARM_PTDUMP)	+= dump.o
+obj-$(CONFIG_ARM_PTDUMP_CORE)	+= dump.o
+obj-$(CONFIG_ARM_PTDUMP_DEBUGFS)	+= ptdump_debugfs.o
 obj-$(CONFIG_MODULES)		+= proc-syms.o
 obj-$(CONFIG_DEBUG_VIRTUAL)	+= physaddr.o
 
diff --git a/arch/arm/mm/dump.c b/arch/arm/mm/dump.c
index fc3b440..8dfe7c3 100644
--- a/arch/arm/mm/dump.c
+++ b/arch/arm/mm/dump.c
@@ -21,11 +21,7 @@
 #include <asm/fixmap.h>
 #include <asm/memory.h>
 #include <asm/pgtable.h>
-
-struct addr_marker {
-	unsigned long start_address;
-	const char *name;
-};
+#include <asm/ptdump.h>
 
 static struct addr_marker address_markers[] = {
 	{ MODULES_VADDR,	"Modules" },
@@ -335,50 +331,36 @@ static void walk_pud(struct pg_state *st, pgd_t *pgd, unsigned long start)
 	}
 }
 
-static void walk_pgd(struct seq_file *m)
+static void walk_pgd(struct pg_state *st, struct mm_struct *mm,
+			unsigned long start)
 {
-	pgd_t *pgd = swapper_pg_dir;
-	struct pg_state st;
-	unsigned long addr;
+	pgd_t *pgd = pgd_offset(mm, 0UL);
 	unsigned i;
-
-	memset(&st, 0, sizeof(st));
-	st.seq = m;
-	st.marker = address_markers;
+	unsigned long addr;
 
 	for (i = 0; i < PTRS_PER_PGD; i++, pgd++) {
-		addr = i * PGDIR_SIZE;
+		addr = start + i * PGDIR_SIZE;
 		if (!pgd_none(*pgd)) {
-			walk_pud(&st, pgd, addr);
+			walk_pud(st, pgd, addr);
 		} else {
-			note_page(&st, addr, 1, pgd_val(*pgd), NULL);
+			note_page(st, addr, 1, pgd_val(*pgd), NULL);
 		}
 	}
-
-	note_page(&st, 0, 0, 0, NULL);
 }
 
-static int ptdump_show(struct seq_file *m, void *v)
+void ptdump_walk_pgd(struct seq_file *m, struct ptdump_info *info)
 {
-	walk_pgd(m);
-	return 0;
-}
+	struct pg_state st = {
+		.seq = m,
+		.marker = info->markers,
+	};
 
-static int ptdump_open(struct inode *inode, struct file *file)
-{
-	return single_open(file, ptdump_show, NULL);
+	walk_pgd(&st, info->mm, info->base_addr);
+	note_page(&st, 0, 0, 0, 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)
+static void ptdump_initialize(void)
 {
-	struct dentry *pe;
 	unsigned i, j;
 
 	for (i = 0; i < ARRAY_SIZE(pg_level); i++)
@@ -387,9 +369,18 @@ static int ptdump_init(void)
 				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;
+static struct ptdump_info kernel_ptdump_info = {
+	.mm = &init_mm,
+	.markers = address_markers,
+	.base_addr = 0,
+};
+
+static int ptdump_init(void)
+{
+	ptdump_initialize();
+	return ptdump_debugfs_register(&kernel_ptdump_info,
+					"kernel_page_tables");
 }
 __initcall(ptdump_init);
diff --git a/arch/arm/mm/ptdump_debugfs.c b/arch/arm/mm/ptdump_debugfs.c
new file mode 100644
index 0000000..be8d87b
--- /dev/null
+++ b/arch/arm/mm/ptdump_debugfs.c
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+
+#include <asm/ptdump.h>
+
+static int ptdump_show(struct seq_file *m, void *v)
+{
+	struct ptdump_info *info = m->private;
+
+	ptdump_walk_pgd(m, info);
+	return 0;
+}
+
+static int ptdump_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, ptdump_show, inode->i_private);
+}
+
+static const struct file_operations ptdump_fops = {
+	.open		= ptdump_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+int ptdump_debugfs_register(struct ptdump_info *info, const char *name)
+{
+	struct dentry *pe;
+
+	pe = debugfs_create_file(name, 0400, NULL, info, &ptdump_fops);
+	return pe ? 0 : -ENOMEM;
+
+}
-- 
1.9.1

Re: [kernel-hardening][PATCH v3 1/3] arm: mm: dump: make page table dumping reusable

[Kees Cook]

On Mon, Dec 4, 2017 at 6:25 AM, Jinbum Park <jinb.park7@gmail.com> wrote:
> This patch refactors the arm page table dumping code,
> so multiple tables may be registered with the framework.
>
> This patch refers below commits of arm64.
> (4674fdb9f149 ("arm64: mm: dump: make page table dumping reusable"))
> (4ddb9bf83349 ("arm64: dump: Make ptdump debugfs a separate option"))
>
> Signed-off-by: Jinbum Park <jinb.park7@gmail.com>
> ---
> v3: No changes
>
>  arch/arm/Kconfig.debug        |  6 +++-
>  arch/arm/include/asm/ptdump.h | 48 ++++++++++++++++++++++++++++++++
>  arch/arm/mm/Makefile          |  3 +-
>  arch/arm/mm/dump.c            | 65 +++++++++++++++++++------------------------
>  arch/arm/mm/ptdump_debugfs.c  | 34 ++++++++++++++++++++++
>  5 files changed, 117 insertions(+), 39 deletions(-)
>  create mode 100644 arch/arm/include/asm/ptdump.h
>  create mode 100644 arch/arm/mm/ptdump_debugfs.c
>
> diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
> index 17685e1..e7b94db 100644
> --- a/arch/arm/Kconfig.debug
> +++ b/arch/arm/Kconfig.debug
> @@ -3,10 +3,14 @@ menu "Kernel hacking"
>
>  source "lib/Kconfig.debug"
>
> -config ARM_PTDUMP
> +config ARM_PTDUMP_CORE
> +       def_bool n
> +
> +config ARM_PTDUMP_DEBUGFS
>         bool "Export kernel pagetable layout to userspace via debugfs"
>         depends on DEBUG_KERNEL
>         depends on MMU
> +       select ARM_PTDUMP_CORE
>         select DEBUG_FS
>         ---help---
>           Say Y here if you want to show the kernel pagetable layout in a
> diff --git a/arch/arm/include/asm/ptdump.h b/arch/arm/include/asm/ptdump.h
> new file mode 100644
> index 0000000..3a6c0b7
> --- /dev/null
> +++ b/arch/arm/include/asm/ptdump.h
> @@ -0,0 +1,48 @@
> +/*
> + * Copyright (C) 2014 ARM Ltd.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +#ifndef __ASM_PTDUMP_H
> +#define __ASM_PTDUMP_H
> +
> +#ifdef CONFIG_ARM_PTDUMP_CORE

Is this #ifdef needed? I think this file is only included in dump.c
and ptdump_debugfs.c, both of which are only built when
CONFIG_ARM_PTDUMP_CORE is defined.

> +
> +#include <linux/mm_types.h>
> +#include <linux/seq_file.h>
> +
> +struct addr_marker {
> +       unsigned long start_address;
> +       char *name;
> +};
> +
> +struct ptdump_info {
> +       struct mm_struct                *mm;
> +       const struct addr_marker        *markers;
> +       unsigned long                   base_addr;
> +};
> +
> +void ptdump_walk_pgd(struct seq_file *s, struct ptdump_info *info);
> +#ifdef CONFIG_ARM_PTDUMP_DEBUGFS
> +int ptdump_debugfs_register(struct ptdump_info *info, const char *name);
> +#else
> +static inline int ptdump_debugfs_register(struct ptdump_info *info,
> +                                       const char *name)
> +{
> +       return 0;
> +}
> +#endif /* CONFIG_ARM_PTDUMP_DEBUGFS */
> +
> +#endif /* CONFIG_ARM_PTDUMP_CORE */
> +
> +#endif /* __ASM_PTDUMP_H */
> diff --git a/arch/arm/mm/Makefile b/arch/arm/mm/Makefile
> index 01bcc33..28be5f4 100644
> --- a/arch/arm/mm/Makefile
> +++ b/arch/arm/mm/Makefile
> @@ -13,7 +13,8 @@ obj-y                         += nommu.o
>  obj-$(CONFIG_ARM_MPU)          += pmsa-v7.o
>  endif
>
> -obj-$(CONFIG_ARM_PTDUMP)       += dump.o
> +obj-$(CONFIG_ARM_PTDUMP_CORE)  += dump.o
> +obj-$(CONFIG_ARM_PTDUMP_DEBUGFS)       += ptdump_debugfs.o
>  obj-$(CONFIG_MODULES)          += proc-syms.o
>  obj-$(CONFIG_DEBUG_VIRTUAL)    += physaddr.o
>
> diff --git a/arch/arm/mm/dump.c b/arch/arm/mm/dump.c
> index fc3b440..8dfe7c3 100644
> --- a/arch/arm/mm/dump.c
> +++ b/arch/arm/mm/dump.c
> @@ -21,11 +21,7 @@
>  #include <asm/fixmap.h>
>  #include <asm/memory.h>
>  #include <asm/pgtable.h>
> -
> -struct addr_marker {
> -       unsigned long start_address;
> -       const char *name;
> -};
> +#include <asm/ptdump.h>
>
>  static struct addr_marker address_markers[] = {
>         { MODULES_VADDR,        "Modules" },
> @@ -335,50 +331,36 @@ static void walk_pud(struct pg_state *st, pgd_t *pgd, unsigned long start)
>         }
>  }
>
> -static void walk_pgd(struct seq_file *m)
> +static void walk_pgd(struct pg_state *st, struct mm_struct *mm,
> +                       unsigned long start)
>  {
> -       pgd_t *pgd = swapper_pg_dir;
> -       struct pg_state st;
> -       unsigned long addr;
> +       pgd_t *pgd = pgd_offset(mm, 0UL);
>         unsigned i;
> -
> -       memset(&st, 0, sizeof(st));
> -       st.seq = m;
> -       st.marker = address_markers;
> +       unsigned long addr;
>
>         for (i = 0; i < PTRS_PER_PGD; i++, pgd++) {
> -               addr = i * PGDIR_SIZE;
> +               addr = start + i * PGDIR_SIZE;
>                 if (!pgd_none(*pgd)) {
> -                       walk_pud(&st, pgd, addr);
> +                       walk_pud(st, pgd, addr);
>                 } else {
> -                       note_page(&st, addr, 1, pgd_val(*pgd), NULL);
> +                       note_page(st, addr, 1, pgd_val(*pgd), NULL);
>                 }
>         }
> -
> -       note_page(&st, 0, 0, 0, NULL);
>  }
>
> -static int ptdump_show(struct seq_file *m, void *v)
> +void ptdump_walk_pgd(struct seq_file *m, struct ptdump_info *info)
>  {
> -       walk_pgd(m);
> -       return 0;
> -}
> +       struct pg_state st = {
> +               .seq = m,
> +               .marker = info->markers,
> +       };
>
> -static int ptdump_open(struct inode *inode, struct file *file)
> -{
> -       return single_open(file, ptdump_show, NULL);
> +       walk_pgd(&st, info->mm, info->base_addr);
> +       note_page(&st, 0, 0, 0, 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)
> +static void ptdump_initialize(void)
>  {
> -       struct dentry *pe;
>         unsigned i, j;
>
>         for (i = 0; i < ARRAY_SIZE(pg_level); i++)
> @@ -387,9 +369,18 @@ static int ptdump_init(void)
>                                 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;
> +static struct ptdump_info kernel_ptdump_info = {
> +       .mm = &init_mm,
> +       .markers = address_markers,
> +       .base_addr = 0,
> +};
> +
> +static int ptdump_init(void)
> +{
> +       ptdump_initialize();
> +       return ptdump_debugfs_register(&kernel_ptdump_info,
> +                                       "kernel_page_tables");

This changes the return value of ptdump_init. This should do similar
to what was done before:

return ptdump_debugfs_register(&kernel_ptdump_info,
"kernel_page_tables") ? 0 : -ENOMEM;


>  }
>  __initcall(ptdump_init);
> diff --git a/arch/arm/mm/ptdump_debugfs.c b/arch/arm/mm/ptdump_debugfs.c
> new file mode 100644
> index 0000000..be8d87b
> --- /dev/null
> +++ b/arch/arm/mm/ptdump_debugfs.c
> @@ -0,0 +1,34 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/debugfs.h>
> +#include <linux/seq_file.h>
> +
> +#include <asm/ptdump.h>
> +
> +static int ptdump_show(struct seq_file *m, void *v)
> +{
> +       struct ptdump_info *info = m->private;
> +
> +       ptdump_walk_pgd(m, info);
> +       return 0;
> +}
> +
> +static int ptdump_open(struct inode *inode, struct file *file)
> +{
> +       return single_open(file, ptdump_show, inode->i_private);
> +}
> +
> +static const struct file_operations ptdump_fops = {
> +       .open           = ptdump_open,
> +       .read           = seq_read,
> +       .llseek         = seq_lseek,
> +       .release        = single_release,
> +};
> +
> +int ptdump_debugfs_register(struct ptdump_info *info, const char *name)
> +{
> +       struct dentry *pe;
> +
> +       pe = debugfs_create_file(name, 0400, NULL, info, &ptdump_fops);
> +       return pe ? 0 : -ENOMEM;
> +
> +}
> --
> 1.9.1
>

-Kees

-- 
Kees Cook
Pixel Security

Re: [kernel-hardening][PATCH v3 1/3] arm: mm: dump: make page table dumping reusable

[Jinbum Park]

>> +#ifndef __ASM_PTDUMP_H
>> +#define __ASM_PTDUMP_H
>> +
>> +#ifdef CONFIG_ARM_PTDUMP_CORE
>
> Is this #ifdef needed? I think this file is only included in dump.c
> and ptdump_debugfs.c, both of which are only built when
> CONFIG_ARM_PTDUMP_CORE is defined.

Looking at next patch in this patch-set series ([PATCH v3 3/3] arm:
mm: dump: add checking for writable and executable pages),
Not only dump.c and ptdump_debugfs.c but also arch/arm/mm/init.c
include this file (ptdump.h) to call debug_checkwx().
mm/init.c is not built only when CONFIG_ARM_PTDUMP_CORE is defined.
So, This #ifdef seems not be needed for this patch, but is needed for
this patch-set series.


>> +static int ptdump_init(void)
>> +{
>> +       ptdump_initialize();
>> +       return ptdump_debugfs_register(&kernel_ptdump_info,
>> +                                       "kernel_page_tables");
>
> This changes the return value of ptdump_init. This should do similar
> to what was done before:
>
> return ptdump_debugfs_register(&kernel_ptdump_info,
> "kernel_page_tables") ? 0 : -ENOMEM;


ptdump_debugfs_register() already returns what you think.

>> +int ptdump_debugfs_register(struct ptdump_info *info, const char *name)
>> +{
>> +       struct dentry *pe;
>> +
>> +       pe = debugfs_create_file(name, 0400, NULL, info, &ptdump_fops);
>> +       return pe ? 0 : -ENOMEM;
>> +
>> +}

So "return ptdump_debugfs_register(~~)" is fine.


Thanks.
Jinbum Park.

Re: [kernel-hardening][PATCH v3 1/3] arm: mm: dump: make page table dumping reusable

[Kees Cook]

On Wed, Dec 6, 2017 at 1:45 AM, Jinbum Park <jinb.park7@gmail.com> wrote:
>>> +#ifndef __ASM_PTDUMP_H
>>> +#define __ASM_PTDUMP_H
>>> +
>>> +#ifdef CONFIG_ARM_PTDUMP_CORE
>>
>> Is this #ifdef needed? I think this file is only included in dump.c
>> and ptdump_debugfs.c, both of which are only built when
>> CONFIG_ARM_PTDUMP_CORE is defined.
>
> Looking at next patch in this patch-set series ([PATCH v3 3/3] arm:
> mm: dump: add checking for writable and executable pages),
> Not only dump.c and ptdump_debugfs.c but also arch/arm/mm/init.c
> include this file (ptdump.h) to call debug_checkwx().
> mm/init.c is not built only when CONFIG_ARM_PTDUMP_CORE is defined.
> So, This #ifdef seems not be needed for this patch, but is needed for
> this patch-set series.
>
>
>>> +static int ptdump_init(void)
>>> +{
>>> +       ptdump_initialize();
>>> +       return ptdump_debugfs_register(&kernel_ptdump_info,
>>> +                                       "kernel_page_tables");
>>
>> This changes the return value of ptdump_init. This should do similar
>> to what was done before:
>>
>> return ptdump_debugfs_register(&kernel_ptdump_info,
>> "kernel_page_tables") ? 0 : -ENOMEM;
>
>
> ptdump_debugfs_register() already returns what you think.
>
>>> +int ptdump_debugfs_register(struct ptdump_info *info, const char *name)
>>> +{
>>> +       struct dentry *pe;
>>> +
>>> +       pe = debugfs_create_file(name, 0400, NULL, info, &ptdump_fops);
>>> +       return pe ? 0 : -ENOMEM;
>>> +
>>> +}
>
> So "return ptdump_debugfs_register(~~)" is fine.

Ah! Yes, I totally missed the change from create_file to
debugfs_register. Sorry for the noise!

-Kees

-- 
Kees Cook
Pixel Security