[PATCH] docs: add documentation on printing kernel addresses
- Date: Thu, 7 Dec 2017 11:26:38 +1100
- From: "Tobin C. Harding" <me@xxxxxxxx>
- Subject: [PATCH] docs: add documentation on printing kernel addresses
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
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 '[*]'
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
@@ -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).
+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.