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SubjectRe: [PATCH] docs: add documentation on printing kernel addresses
Please drop this patch, needs amendment (commented inline).

On Thu, Dec 07, 2017 at 11:26:38AM +1100, Tobin C. Harding 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@tobin.cc>
> ---
>
> Is there a proffered method for subscripts in sphinx kernel docs? Here
> we use '[*]'
>
> thanks,
> Tobin.
>
> 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.

[*] If KALLSYMS is enabled and symbol lookup fails, the raw address is
currently printed. If KALLSYMS is not enabled the address is printed.

thanks,
Tobin.

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