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

From: Kees Cook
Date: Tue Dec 05 2017 - 14:53:21 EST

On Mon, Dec 4, 2017 at 6:25 AM, Jinbum Park <jinb.park7@xxxxxxxxx> 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@xxxxxxxxx>
> ---
> 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