Messages in this thread Patch in this message | | | From | "Tobin C. Harding" <> | Subject | [PATCH] docs: add documentation on printing kernel addresses | Date | Thu, 7 Dec 2017 11:26:38 +1100 |
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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. + Unique identifiers ------------------ -- 2.7.4
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