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Date: Wed, 25 Nov 2015 15:31:22 -0800
From: Kees Cook <>
Cc: Kees Cook <>, Andy Lutomirski <>,
        "H. Peter Anvin" <>,
        Michael Ellerman <>,
        Mathias Krause <>,
        Ingo Molnar <>, Thomas Gleixner <>,, Arnd Bergmann <>,
        PaX Team <>, Emese Revfy <>,,
        linux-arch <>
Subject: [PATCH v2 0/4] introduce post-init read-only memory

One of the easiest ways to protect the kernel from attack is to reduce
the internal attack surface exposed when a "write" flaw is available. By
making as much of the kernel read-only as possible, we reduce the
attack surface.

Many things are written to only during __init, and never changed
again. These cannot be made "const" since the compiler will do the wrong
thing (we do actually need to write to them). Instead, move these items
into a memory region that will be made read-only during mark_rodata_ro()
which happens after all kernel __init code has finished.

This introduces __ro_after_init as a way to mark such memory, and uses
it on the x86 vDSO to kill an extant kernel exploitation method. Also
adds a new kernel parameter to help debug future use and adds an lkdtm
test to check the results.


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