2011-02-22 19:33:28

by Kees Cook

[permalink] [raw]
Subject: [PATCH] acpi: create CONFIG item for debugfs custom_method

Since /sys/kernel/debug/acpi/custom_method can be used to write arbitrary
kernel memory (http://jon.oberheide.org/files/american-sign-language.c),
it should be able to be left out of the kernel for system owners that
want to be as defensive as possible to potential attacks, even from the
root user. See as examples: CONFIG_DEVKMEM, CONFIG_STRICT_DEVMEM, and
/proc/sys/kernel/modules_disabled.

Signed-off-by: Kees Cook <[email protected]>
---
drivers/acpi/Kconfig | 10 ++++++++++
drivers/acpi/debugfs.c | 2 ++
2 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 2aa042a..726b7ea 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -381,6 +381,16 @@ config ACPI_HED
which is used to report some hardware errors notified via
SCI, mainly the corrected errors.

+config ACPI_DEBUG_CUSTOM_METHOD
+ bool "Debugging: Custom Method Insertion"
+ depends on DEBUG_FS
+ default n
+ help
+ This creates the debugfs interface file "acpi/custom_method"
+ used for loading custom ACPI methods. Note that this allows
+ arbitrary kernel memory writing by the root user and is not
+ recommended for normal systems.
+
source "drivers/acpi/apei/Kconfig"

endif # ACPI
diff --git a/drivers/acpi/debugfs.c b/drivers/acpi/debugfs.c
index 5df67f1..0240b15 100644
--- a/drivers/acpi/debugfs.c
+++ b/drivers/acpi/debugfs.c
@@ -20,6 +20,7 @@ module_param_named(aml_debug_output, acpi_gbl_enable_aml_debug_object,
MODULE_PARM_DESC(aml_debug_output,
"To enable/disable the ACPI Debug Object output.");

+#ifdef CONFIG_ACPI_DEBUG_CUSTOM_METHOD
/* /sys/kernel/debug/acpi/custom_method */

static ssize_t cm_write(struct file *file, const char __user * user_buf,
@@ -92,3 +93,4 @@ err:
debugfs_remove(acpi_dir);
return -EINVAL;
}
+#endif
--
1.7.2.3

--
Kees Cook
Ubuntu Security Team


2011-04-13 00:21:55

by Kees Cook

[permalink] [raw]
Subject: Re: [PATCH] acpi: create CONFIG item for debugfs custom_method

Hi,

Any news on this? I think it's a no-brainer to let this be CONFIG-able.

Thanks!

-Kees

On Tue, Feb 22, 2011 at 11:32:50AM -0800, Kees Cook wrote:
> Since /sys/kernel/debug/acpi/custom_method can be used to write arbitrary
> kernel memory (http://jon.oberheide.org/files/american-sign-language.c),
> it should be able to be left out of the kernel for system owners that
> want to be as defensive as possible to potential attacks, even from the
> root user. See as examples: CONFIG_DEVKMEM, CONFIG_STRICT_DEVMEM, and
> /proc/sys/kernel/modules_disabled.
>
> Signed-off-by: Kees Cook <[email protected]>
> ---
> drivers/acpi/Kconfig | 10 ++++++++++
> drivers/acpi/debugfs.c | 2 ++
> 2 files changed, 12 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> index 2aa042a..726b7ea 100644
> --- a/drivers/acpi/Kconfig
> +++ b/drivers/acpi/Kconfig
> @@ -381,6 +381,16 @@ config ACPI_HED
> which is used to report some hardware errors notified via
> SCI, mainly the corrected errors.
>
> +config ACPI_DEBUG_CUSTOM_METHOD
> + bool "Debugging: Custom Method Insertion"
> + depends on DEBUG_FS
> + default n
> + help
> + This creates the debugfs interface file "acpi/custom_method"
> + used for loading custom ACPI methods. Note that this allows
> + arbitrary kernel memory writing by the root user and is not
> + recommended for normal systems.
> +
> source "drivers/acpi/apei/Kconfig"
>
> endif # ACPI
> diff --git a/drivers/acpi/debugfs.c b/drivers/acpi/debugfs.c
> index 5df67f1..0240b15 100644
> --- a/drivers/acpi/debugfs.c
> +++ b/drivers/acpi/debugfs.c
> @@ -20,6 +20,7 @@ module_param_named(aml_debug_output, acpi_gbl_enable_aml_debug_object,
> MODULE_PARM_DESC(aml_debug_output,
> "To enable/disable the ACPI Debug Object output.");
>
> +#ifdef CONFIG_ACPI_DEBUG_CUSTOM_METHOD
> /* /sys/kernel/debug/acpi/custom_method */
>
> static ssize_t cm_write(struct file *file, const char __user * user_buf,
> @@ -92,3 +93,4 @@ err:
> debugfs_remove(acpi_dir);
> return -EINVAL;
> }
> +#endif
> --
> 1.7.2.3
>
> --
> Kees Cook
> Ubuntu Security Team
--
Kees Cook
Ubuntu Security Team

2011-05-28 04:19:37

by Kees Cook

[permalink] [raw]
Subject: [PATCH] acpi: create CONFIG item for debugfs custom_method

Since /sys/kernel/debug/acpi/custom_method can be used to write arbitrary
kernel memory (http://jon.oberheide.org/files/american-sign-language.c),
it should be able to be left out of the kernel for system owners that
want to be as defensive as possible to potential attacks, even from the
root user. See as examples: CONFIG_DEVKMEM, CONFIG_STRICT_DEVMEM, and
/proc/sys/kernel/modules_disabled.

Signed-off-by: Kees Cook <[email protected]>
---
Third time sending this, no response...
https://lkml.org/lkml/2011/2/22/369

drivers/acpi/Kconfig | 10 ++++++++++
drivers/acpi/debugfs.c | 2 ++
2 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 2aa042a..726b7ea 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -381,6 +381,16 @@ config ACPI_HED
which is used to report some hardware errors notified via
SCI, mainly the corrected errors.

+config ACPI_DEBUG_CUSTOM_METHOD
+ bool "Debugging: Custom Method Insertion"
+ depends on DEBUG_FS
+ default n
+ help
+ This creates the debugfs interface file "acpi/custom_method"
+ used for loading custom ACPI methods. Note that this allows
+ arbitrary kernel memory writing by the root user and is not
+ recommended for normal systems.
+
source "drivers/acpi/apei/Kconfig"

endif # ACPI
diff --git a/drivers/acpi/debugfs.c b/drivers/acpi/debugfs.c
index 5df67f1..0240b15 100644
--- a/drivers/acpi/debugfs.c
+++ b/drivers/acpi/debugfs.c
@@ -20,6 +20,7 @@ module_param_named(aml_debug_output, acpi_gbl_enable_aml_debug_object,
MODULE_PARM_DESC(aml_debug_output,
"To enable/disable the ACPI Debug Object output.");

+#ifdef CONFIG_ACPI_DEBUG_CUSTOM_METHOD
/* /sys/kernel/debug/acpi/custom_method */

static ssize_t cm_write(struct file *file, const char __user * user_buf,
@@ -92,3 +93,4 @@ err:
debugfs_remove(acpi_dir);
return -EINVAL;
}
+#endif
--
1.7.2.3

--
Kees Cook
Ubuntu Security Team

2011-05-28 09:02:56

by Rafael J. Wysocki

[permalink] [raw]
Subject: Re: [PATCH] acpi: create CONFIG item for debugfs custom_method

On Saturday, May 28, 2011, Kees Cook wrote:
> Since /sys/kernel/debug/acpi/custom_method can be used to write arbitrary
> kernel memory (http://jon.oberheide.org/files/american-sign-language.c),
> it should be able to be left out of the kernel for system owners that
> want to be as defensive as possible to potential attacks, even from the
> root user. See as examples: CONFIG_DEVKMEM, CONFIG_STRICT_DEVMEM, and
> /proc/sys/kernel/modules_disabled.

I believe Thomas Renninger sent patches to address this issue too.

Thanks,
Rafael


> Signed-off-by: Kees Cook <[email protected]>
> ---
> Third time sending this, no response...
> https://lkml.org/lkml/2011/2/22/369
>
> drivers/acpi/Kconfig | 10 ++++++++++
> drivers/acpi/debugfs.c | 2 ++
> 2 files changed, 12 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> index 2aa042a..726b7ea 100644
> --- a/drivers/acpi/Kconfig
> +++ b/drivers/acpi/Kconfig
> @@ -381,6 +381,16 @@ config ACPI_HED
> which is used to report some hardware errors notified via
> SCI, mainly the corrected errors.
>
> +config ACPI_DEBUG_CUSTOM_METHOD
> + bool "Debugging: Custom Method Insertion"
> + depends on DEBUG_FS
> + default n
> + help
> + This creates the debugfs interface file "acpi/custom_method"
> + used for loading custom ACPI methods. Note that this allows
> + arbitrary kernel memory writing by the root user and is not
> + recommended for normal systems.
> +
> source "drivers/acpi/apei/Kconfig"
>
> endif # ACPI
> diff --git a/drivers/acpi/debugfs.c b/drivers/acpi/debugfs.c
> index 5df67f1..0240b15 100644
> --- a/drivers/acpi/debugfs.c
> +++ b/drivers/acpi/debugfs.c
> @@ -20,6 +20,7 @@ module_param_named(aml_debug_output, acpi_gbl_enable_aml_debug_object,
> MODULE_PARM_DESC(aml_debug_output,
> "To enable/disable the ACPI Debug Object output.");
>
> +#ifdef CONFIG_ACPI_DEBUG_CUSTOM_METHOD
> /* /sys/kernel/debug/acpi/custom_method */
>
> static ssize_t cm_write(struct file *file, const char __user * user_buf,
> @@ -92,3 +93,4 @@ err:
> debugfs_remove(acpi_dir);
> return -EINVAL;
> }
> +#endif
>

2011-05-29 05:40:07

by Len Brown

[permalink] [raw]
Subject: Re: [PATCH] acpi: create CONFIG item for debugfs custom_method

applied

thanks,
Len Brown, Intel Open Source Technology Center

2011-05-29 05:51:31

by Len Brown

[permalink] [raw]
Subject: Re: [PATCH] acpi: create CONFIG item for debugfs custom_method

> applied

un-applied - forgot I had Thomas' version already pending.

> thanks,
> Len Brown, Intel Open Source Technology Center