Date: Wed, 20 Dec 2017 08:17:17 +1100 From: "Tobin C. Harding" <me@...in.cc> To: Jonathan Corbet <corbet@....net> Cc: "Tobin C. Harding" <me@...in.cc>, Randy Dunlap <rdunlap@...radead.org>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>, Alexander Popov <alex.popov@...ux.com>, Joe Perches <joe@...ches.com>, kernel-hardening@...ts.openwall.com Subject: [PATCH v4 3/3] doc: 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. Other documentation was updated but security/self-protection missed out. Add self-protection documentation regarding printing kernel addresses. Signed-off-by: Tobin C. Harding <me@...in.cc> --- Documentation/security/self-protection.rst | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/Documentation/security/self-protection.rst b/Documentation/security/self-protection.rst index 60c8bd8b77bf..0f53826c78b9 100644 --- a/Documentation/security/self-protection.rst +++ b/Documentation/security/self-protection.rst @@ -270,6 +270,21 @@ 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 KALLSYMS is enabled and symbol lookup fails, the raw address is +printed. If KALLSYMS is not enabled the raw address is printed. + Unique identifiers ------------------ -- 2.7.4
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