Re: [PATCH] docs: add documentation on printing kernel addresses
- Date: Wed, 6 Dec 2017 16:43:40 -0800
- From: Kees Cook <keescook@xxxxxxxxxxxx>
- Subject: Re: [PATCH] docs: add documentation on printing kernel addresses
On Wed, Dec 6, 2017 at 4:26 PM, Tobin C. Harding <me@xxxxxxxx> wrote:
> Hashing addresses printed with printk specifier %p was implemented
> recently. During development a number of issues were raised regarding
> leaking kernel addresses to userspace. We should update the
> documentation appropriately.
> Add documentation regarding printing kernel addresses.
> Signed-off-by: Tobin C. Harding <me@xxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Is there a proffered method for subscripts in sphinx kernel docs? Here
> we use '[*]'
Great question... I can't find an answer to this. :P
> Documentation/security/self-protection.rst | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
> diff --git a/Documentation/security/self-protection.rst b/Documentation/security/self-protection.rst
> index 60c8bd8b77bf..e711280cfdd7 100644
> --- a/Documentation/security/self-protection.rst
> +++ b/Documentation/security/self-protection.rst
> @@ -270,6 +270,20 @@ attacks, it is important to defend against exposure of both kernel memory
> addresses and kernel memory contents (since they may contain kernel
> addresses or other sensitive things like canary values).
> +Kernel addresses
> +Printing kernel addresses to userspace leaks sensitive information about
> +the kernel memory layout. Care should be exercised when using any printk
> +specifier that prints the raw address, currently %px, %p[ad], (and %p[sSb]
> +in certain circumstances [*]). Any file written to using one of these
> +specifiers should be readable only by privileged processes.
> +Kernels 4.14 and older printed the raw address using %p. As of 4.15-rc1
> +addresses printed with the specifier %p are hashed before printing.
> +[*] If symbol lookup fails, the raw address is currently printed.
Is there a plan to adjust this case?
> Unique identifiers