Re: Security fix for remapping of page 0 (was [PATCH] Change ZERO_SIZE_PTR to point at unmapped space)

James Morris
2009-06-04T02:41:46Z

On Wed, 3 Jun 2009, Christoph Lameter wrote:

> Use mmap_min_addr indepedently of security models
>
> This patch removes the dependency of mmap_min_addr on CONFIG_SECURITY.
> It also sets a default mmap_min_addr of 4096.
>
> mmapping of addresses below 4096 will only be possible for processes
> with CAP_SYS_RAWIO.
>
>
> Signed-off-by: Christoph Lameter <cl@linux-foundation.org>

Applied to
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6#next

>
> ---
> include/linux/mm.h | 2 --
> include/linux/security.h | 2 ++
> kernel/sysctl.c | 2 --
> mm/Kconfig | 19 +++++++++++++++++++
> mm/mmap.c | 3 +++
> security/Kconfig | 20 --------------------
> security/security.c | 3 ---
> 7 files changed, 24 insertions(+), 27 deletions(-)
>
> Index: linux-2.6/include/linux/mm.h
> ===================================================================
> --- linux-2.6.orig/include/linux/mm.h 2009-06-03 15:00:54.000000000 -0500
> +++ linux-2.6/include/linux/mm.h 2009-06-03 15:00:56.000000000 -0500
> @@ -580,12 +580,10 @@ static inline void set_page_links(struct
> */
> static inline unsigned long round_hint_to_min(unsigned long hint)
> {
> -#ifdef CONFIG_SECURITY
> hint &= PAGE_MASK;
> if (((void *)hint != NULL) &&
> (hint < mmap_min_addr))
> return PAGE_ALIGN(mmap_min_addr);
> -#endif
> return hint;
> }
>
> Index: linux-2.6/kernel/sysctl.c
> ===================================================================
> --- linux-2.6.orig/kernel/sysctl.c 2009-06-03 15:00:54.000000000 -0500
> +++ linux-2.6/kernel/sysctl.c 2009-06-03 15:00:56.000000000 -0500
> @@ -1225,7 +1225,6 @@ static struct ctl_table vm_table[] = {
> .strategy = &sysctl_jiffies,
> },
> #endif
> -#ifdef CONFIG_SECURITY
> {
> .ctl_name = CTL_UNNUMBERED,
> .procname = "mmap_min_addr",
> @@ -1234,7 +1233,6 @@ static struct ctl_table vm_table[] = {
> .mode = 0644,
> .proc_handler = &proc_doulongvec_minmax,
> },
> -#endif
> #ifdef CONFIG_NUMA
> {
> .ctl_name = CTL_UNNUMBERED,
> Index: linux-2.6/mm/mmap.c
> ===================================================================
> --- linux-2.6.orig/mm/mmap.c 2009-06-03 15:00:54.000000000 -0500
> +++ linux-2.6/mm/mmap.c 2009-06-03 15:01:18.000000000 -0500
> @@ -87,6 +87,9 @@ int sysctl_overcommit_ratio = 50; /* def
> int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
> struct percpu_counter vm_committed_as;
>
> +/* amount of vm to protect from userspace access */
> +unsigned long mmap_min_addr = CONFIG_DEFAULT_MMAP_MIN_ADDR;
> +
> /*
> * Check that a process has enough memory to allocate a new virtual
> * mapping. 0 means there is enough memory for the allocation to
> Index: linux-2.6/security/security.c
> ===================================================================
> --- linux-2.6.orig/security/security.c 2009-06-03 15:00:54.000000000 -0500
> +++ linux-2.6/security/security.c 2009-06-03 15:00:56.000000000 -0500
> @@ -26,9 +26,6 @@ extern void security_fixup_ops(struct se
>
> struct security_operations *security_ops; /* Initialized to NULL */
>
> -/* amount of vm to protect from userspace access */
> -unsigned long mmap_min_addr = CONFIG_SECURITY_DEFAULT_MMAP_MIN_ADDR;
> -
> static inline int verify(struct security_operations *ops)
> {
> /* verify the security_operations structure exists */
> Index: linux-2.6/mm/Kconfig
> ===================================================================
> --- linux-2.6.orig/mm/Kconfig 2009-06-03 15:00:54.000000000 -0500
> +++ linux-2.6/mm/Kconfig 2009-06-03 15:00:56.000000000 -0500
> @@ -226,6 +226,25 @@ config HAVE_MLOCKED_PAGE_BIT
> config MMU_NOTIFIER
> bool
>
> +config DEFAULT_MMAP_MIN_ADDR
> + int "Low address space to protect from user allocation"
> + default 4096
> + help
> + This is the portion of low virtual memory which should be protected
> + from userspace allocation. Keeping a user from writing to low pages
> + can help reduce the impact of kernel NULL pointer bugs.
> +
> + For most ia64, ppc64 and x86 users with lots of address space
> + a value of 65536 is reasonable and should cause no problems.
> + On arm and other archs it should not be higher than 32768.
> + Programs which use vm86 functionality would either need additional
> + permissions from either the LSM or the capabilities module or have
> + this protection disabled.
> +
> + This value can be changed after boot using the
> + /proc/sys/vm/mmap_min_addr tunable.
> +
> +
> config NOMMU_INITIAL_TRIM_EXCESS
> int "Turn on mmap() excess space trimming before booting"
> depends on !MMU
> Index: linux-2.6/security/Kconfig
> ===================================================================
> --- linux-2.6.orig/security/Kconfig 2009-06-03 15:00:54.000000000 -0500
> +++ linux-2.6/security/Kconfig 2009-06-03 15:00:56.000000000 -0500
> @@ -113,26 +113,6 @@ config SECURITY_ROOTPLUG
>
> If you are unsure how to answer this question, answer N.
>
> -config SECURITY_DEFAULT_MMAP_MIN_ADDR
> - int "Low address space to protect from user allocation"
> - depends on SECURITY
> - default 0
> - help
> - This is the portion of low virtual memory which should be protected
> - from userspace allocation. Keeping a user from writing to low pages
> - can help reduce the impact of kernel NULL pointer bugs.
> -
> - For most ia64, ppc64 and x86 users with lots of address space
> - a value of 65536 is reasonable and should cause no problems.
> - On arm and other archs it should not be higher than 32768.
> - Programs which use vm86 functionality would either need additional
> - permissions from either the LSM or the capabilities module or have
> - this protection disabled.
> -
> - This value can be changed after boot using the
> - /proc/sys/vm/mmap_min_addr tunable.
> -
> -
> source security/selinux/Kconfig
> source security/smack/Kconfig
> source security/tomoyo/Kconfig
> Index: linux-2.6/include/linux/security.h
> ===================================================================
> --- linux-2.6.orig/include/linux/security.h 2009-06-03 15:01:28.000000000 -0500
> +++ linux-2.6/include/linux/security.h 2009-06-03 15:01:42.000000000 -0500
> @@ -2197,6 +2197,8 @@ static inline int security_file_mmap(str
> unsigned long addr,
> unsigned long addr_only)
> {
> + if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
> + return -EACCES;
> return 0;
> }
>
> --
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--
James Morris
<jmorris@namei.org>