Date: Thu, 6 Apr 2017 14:18:15 -0700 From: Kees Cook <keescook@...omium.org> To: kernel-hardening@...ts.openwall.com Cc: Kees Cook <keescook@...omium.org>, Michael Leibowitz <michael.leibowitz@...el.com> Subject: [PATCH 00/18] Introduce struct layout randomization plugin This series brings grsecurity's structure layout randomization plugin to upstream. The plugin randomizes the layout of selected structures at compile time, as a probabilistic defense against attacks that need to know the layout of structures within the kernel. While less useful for distribution kernels (where the randomization seed must be exposed for third party kernel module builds), it still has some value there since now all kernel builds would need to be tracked by an attacker. It is most useful to "in-house" kernel builds where the randomization seed is not available to an attacker. One requirement of the plugin is that randomized structures must use designated initializers. Many of these have been landing already as I've been sending them over the past couple months, but there are still some stragglers, which are included here. Another area to address are places where randomized structures are cast to other structures, since there may be implicit positional details that need to be addressed. Luckily, there are only a few of these false positives, and they have been worked around either by adjusting the source or whitelisting them in the plugin. The plugin selects structures in two ways: manually marked with the new __randomize_layout annotation, or automatically when a structure is found to consist entirely of function pointers (which can be opted out of with the new __no_randomize_layout annotation). A structure that is especially sensitive and regularly abused in exploits is task_struct, but randomizing it requires some special handling due to some fields needing to be at the start and end. To deal with this, an internal anonymous struct is used to mark the portion that will be randomized. I'd love feedback on whether I should bite the bullet and perform indenting or violate indenting rules to avoid a massive white-space change. As mentioned, the bulk of this feature is ported over from grsecurity. The implementation is almost entirely identical to the original code written by Brad Spengler and the PaX Team and Brad Spengler. The changes are addition of improved designated initializer markings, a whitelisting mechanism, and a different approach to handling the task_struct randomization. I've been doing boot tests with instrumentation showing successfully changing offsets within the task_struct, which ran overnight without problems. So far, the 0day builder hasn't alerted on anything, but it's probably still a bit early. This series is based on next-20170404. Patches are: [PATCH 01/18] gcc-plugins: Add the randstruct plugin The plugin itself, with struct auto-detection disabled. [PATCH 02/18] compiler: Add __designated_init annotation [PATCH 03/18] randstruct: Set designated_init attribute Adds marking of structures needing designated initialization. [PATCH 04/18] randstruct: Differentiate bad cast warnings Minor clarifications to bad cast warning output. [PATCH 05/18] af_unix: Use designated initializers Designated initializer fix for af_unix (taken for -next already) https://lkml.org/lkml/2017/4/6/846 [PATCH 06/18] NFS: Avoid cross-structure casting Avoids a false positive in casting (waiting for feedback) https://lkml.org/lkml/2017/4/5/530 [PATCH 07/18] randstruct: Whitelist struct security_hook_heads cast [PATCH 08/18] randstruct: Whitelist UNIXCB cast Whitelist two more false positive cases where source-level fixes aren't obvious/possible. [PATCH 09/18] randstruct: Mark various structs for randomization Adds the manual annotation for structures to randomize. [PATCH 10/18] scsi/bfa: use designated initializers [PATCH 11/18] scsi: qedi,qedf: Use designated initializers [PATCH 12/18] ovl: Use designated initializers The remaining designated initializer fixes for automatic struct randomization. [PATCH 13/18] randstruct: opt-out externally exposed function pointer Opt out of some externally-exposed structs that would be otherwise automatically randomized. [PATCH 14/18] randstruct: Disable randomization of ACPICA structs Temporary disabling of automatic randomization of ACPICA struct. [PATCH 15/18] randstruct: Enable function pointer struct detection Enables automatic struct randomization. [PATCH 16/18] task_struct: Allow randomized layout Adds selected portion of task_struct to be randomized. [PATCH 17/18] sgi-xp: Use designated initializers Enable randomization of sgi-xp struct, pending feedback. https://lkml.org/lkml/2017/3/29/808 [PATCH 18/18] ACPICA: Use designated initializers Enable randomization of ACPICA struct, pending feedback. https://github.com/acpica/acpica/pull/248/ Testing/feedback appreciated! -Kees
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