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Re: [PATCH v2 04/20] gcc-plugins: Add the randstruct plugin

Message ID CAGXu5j+P7Sj99DdYE0mL1fjzVUoK6qntJXhSLk-vnKhHjejd7g@mail.gmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

Kees Cook June 30, 2017, 12:04 a.m. UTC 
On Thu, Jun 29, 2017 at 3:53 PM, Kees Cook <keescook@chromium.org> wrote:
> I see a few possible solutions:

Or this ugly hack:



I suspect updating the ARM assembly (CONFIG-conditionally) to accept
>4095 offsets is probably the best solution.

-Kees
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Patch

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e2ad3531e7fe..5d131f9f1dac 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -749,6 +749,19 @@  struct task_struct {
        /* Namespaces: */
        struct nsproxy                  *nsproxy;

+#ifdef CONFIG_ARM
+       /*
+        * Since task_struct is gigantic, some asmoffset locations
+        * (e.g. TSK_STACK_CANARY) for a randomized field may exceed
+        * an architecture's instruction immediate values. As a
+        * work-around to avoid changing the performance characteristics
+        * of the assembly, split the randomization into two groups,
+        * keeping the "early" fields within range of the immediates.
+        */
+       randomized_struct_fields_end
+       randomized_struct_fields_start
+#endif
+
        /* Signal handlers: */
        struct signal_struct            *signal;
        struct sighand_struct           *sighand;