linux-kernel - Re: [PATCH v4 1/4] SROP Mitigation: Architecture independent code for signal cookies

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Date:	Thu, 31 Mar 2016 15:25:16 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Scott Bauer <sbauer@....utah.edu>
Cc:	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	x86@...nel.org, ak@...ux.intel.com, luto@...capital.net,
	mingo@...hat.com, tglx@...utronix.de, wmealing@...hat.com,
	torvalds@...ux-foundation.org,
	Abhiram Balasubramanian <abhiram@...utah.edu>,
	Scott Bauer <sbauer@...donthack.me>
Subject: Re: [PATCH v4 1/4] SROP Mitigation: Architecture independent code for signal cookies

Scott Bauer <sbauer@....utah.edu> writes:

> This patch adds a per-process secret to the task struct which
> will be used during signal delivery and during a sigreturn.
> Also, logic is added in signal.c to generate, place, extract,
> clear and verify the signal cookie.
>
> Cc: Abhiram Balasubramanian <abhiram@...utah.edu>
> Signed-off-by: Scott Bauer <sbauer@...donthack.me>
> Signed-off-by: Scott Bauer <sbauer@....utah.edu>

> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 60bba7e..1828fb8 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1502,6 +1502,13 @@ struct task_struct {
>  	unsigned long stack_canary;
>  #endif
>  	/*
> +	 * Canary value for signal frames placed on user stack.
> +	 * This helps mitigate "Signal Return oriented program"
> +	 * exploits in userland.
> +	 */
> +	unsigned long sig_cookie;


I suspect we want this to be a per-mm attribute rather than a per-thread
attribute.

Otherwise you are breaking anything that uses a N-M threading model.
Which I suspect means that this implementation choice breaks all go
programs on linux.

> +	/*
>  	 * pointers to (original) parent process, youngest child, younger sibling,
>  	 * older sibling, respectively.  (p->father can be replaced with
>  	 * p->real_parent->pid)

Eric