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> --- 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. + Unique identifiers ------------------ -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
