Mailing List Archive: [PATCH 5/6] notifiers: Use CHECK_DATA

[PATCH 5/6] notifiers: Use CHECK_DATA_CORRUPTION() on checks

Mar 6, 2017, 12:20 PM

Post #1 of 4 (12 views)

When performing notifier function pointer sanity checking, allow
CONFIG_BUG_ON_DATA_CORRUPTION to upgrade from a WARN to a BUG.
Additionally enables CONFIG_DEBUG_NOTIFIERS when selecting
CONFIG_BUG_ON_DATA_CORRUPTION.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
kernel/notifier.c | 5 +++--
lib/Kconfig.debug | 3 ++-
2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/notifier.c b/kernel/notifier.c
index 6196af8a8223..58cc14958d92 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -84,8 +84,9 @@ static int notifier_call_chain(struct notifier_block **nl,
next_nb = rcu_dereference_raw(nb->next);

#ifdef CONFIG_DEBUG_NOTIFIERS
- if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
- WARN(1, "Invalid notifier called!");
+ if (CHECK_DATA_CORRUPTION(
+ !func_ptr_is_kernel_text(nb->notifier_call),
+ "Invalid notifier called!")) {
nb = next_nb;
continue;
}
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 42c61cfe7d19..70e9f2c1bb30 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1277,7 +1277,7 @@ config DEBUG_SG

config DEBUG_NOTIFIERS
bool "Debug notifier call chains"
- depends on DEBUG_KERNEL
+ depends on DEBUG_KERNEL || BUG_ON_DATA_CORRUPTION
help
Enable this to turn on sanity checking for notifier call chains.
This is most useful for kernel developers to make sure that
@@ -1995,6 +1995,7 @@ config BUG_ON_DATA_CORRUPTION
bool "Trigger a BUG when data corruption is detected"
select DEBUG_CREDENTIALS
select DEBUG_LIST
+ select DEBUG_NOTIFIERS
select DEBUG_SG
help
This option enables several inexpensive data corruption checks.
--
2.7.4

Re: [PATCH 5/6] notifiers: Use CHECK_DATA_CORRUPTION() on checks [ In reply to ]

keescook at chromium

Mar 22, 2017, 2:20 PM

Post #2 of 4 (12 views)

Permalink

On Mon, Mar 6, 2017 at 11:09 AM, Kees Cook <keescook@chromium.org> wrote:
> When performing notifier function pointer sanity checking, allow
> CONFIG_BUG_ON_DATA_CORRUPTION to upgrade from a WARN to a BUG.
> Additionally enables CONFIG_DEBUG_NOTIFIERS when selecting
> CONFIG_BUG_ON_DATA_CORRUPTION.

Any feedback on this change? By default, this retains the existing
WARN behavior...

-Kees

>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> kernel/notifier.c | 5 +++--
> lib/Kconfig.debug | 3 ++-
> 2 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/notifier.c b/kernel/notifier.c
> index 6196af8a8223..58cc14958d92 100644
> --- a/kernel/notifier.c
> +++ b/kernel/notifier.c
> @@ -84,8 +84,9 @@ static int notifier_call_chain(struct notifier_block **nl,
> next_nb = rcu_dereference_raw(nb->next);
>
> #ifdef CONFIG_DEBUG_NOTIFIERS
> - if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
> - WARN(1, "Invalid notifier called!");
> + if (CHECK_DATA_CORRUPTION(
> + !func_ptr_is_kernel_text(nb->notifier_call),
> + "Invalid notifier called!")) {
> nb = next_nb;
> continue;
> }
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 42c61cfe7d19..70e9f2c1bb30 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1277,7 +1277,7 @@ config DEBUG_SG
>
> config DEBUG_NOTIFIERS
> bool "Debug notifier call chains"
> - depends on DEBUG_KERNEL
> + depends on DEBUG_KERNEL || BUG_ON_DATA_CORRUPTION
> help
> Enable this to turn on sanity checking for notifier call chains.
> This is most useful for kernel developers to make sure that
> @@ -1995,6 +1995,7 @@ config BUG_ON_DATA_CORRUPTION
> bool "Trigger a BUG when data corruption is detected"
> select DEBUG_CREDENTIALS
> select DEBUG_LIST
> + select DEBUG_NOTIFIERS
> select DEBUG_SG
> help
> This option enables several inexpensive data corruption checks.
> --
> 2.7.4
>

--
Kees Cook
Pixel Security

Re: [PATCH 5/6] notifiers: Use CHECK_DATA_CORRUPTION() on checks [ In reply to ]

arjan at linux

Mar 22, 2017, 2:20 PM

Post #3 of 4 (12 views)

Permalink

On 3/22/2017 12:29 PM, Kees Cook wrote:
>> When performing notifier function pointer sanity checking, allow
>> CONFIG_BUG_ON_DATA_CORRUPTION to upgrade from a WARN to a BUG.
>> Additionally enables CONFIG_DEBUG_NOTIFIERS when selecting
>> CONFIG_BUG_ON_DATA_CORRUPTION.

> Any feedback on this change? By default, this retains the existing
> WARN behavior...

if you're upgrading, is the end point really a panic() ?
e.g. do you assume people to also set panic-on-oops?

Re: [PATCH 5/6] notifiers: Use CHECK_DATA_CORRUPTION() on checks [ In reply to ]

keescook at chromium

Mar 22, 2017, 2:20 PM

Post #4 of 4 (12 views)

Permalink

On Wed, Mar 22, 2017 at 12:32 PM, Arjan van de Ven
<arjan@linux.intel.com> wrote:
> On 3/22/2017 12:29 PM, Kees Cook wrote:
>>>
>>> When performing notifier function pointer sanity checking, allow
>>> CONFIG_BUG_ON_DATA_CORRUPTION to upgrade from a WARN to a BUG.
>>> Additionally enables CONFIG_DEBUG_NOTIFIERS when selecting
>>> CONFIG_BUG_ON_DATA_CORRUPTION.
>
>
>> Any feedback on this change? By default, this retains the existing
>> WARN behavior...
>
>
> if you're upgrading, is the end point really a panic() ?
> e.g. do you assume people to also set panic-on-oops?

That's one option, yes. With the BUG, the process associated is killed
(which is the first level of defense upgrade), and if a system is also
set to panic-on-oops, the entire system will panic (and usually such
systems also retain their crash consoles in some fashion for later
analysis, etc).

-Kees

--
Kees Cook
Pixel Security