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Date: Thu, 29 Jun 2017 17:04:46 -0700
From: Kees Cook <keescook@...omium.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>, Laura Abbott <labbott@...hat.com>,
"the arch/x86 maintainers" <x86@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 04/20] gcc-plugins: Add the randstruct plugin
On Thu, Jun 29, 2017 at 3:53 PM, Kees Cook <keescook@...omium.org> wrote:
> I see a few possible solutions:
Or this ugly hack:
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;
I suspect updating the ARM assembly (CONFIG-conditionally) to accept
>4095 offsets is probably the best solution.
-Kees
--
Kees Cook
Pixel Security
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