From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:58716 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753645AbeDFNfS (ORCPT ); Fri, 6 Apr 2018 09:35:18 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg Kroah-Hartman , Will Deacon , Catalin Marinas , Greg Hackmann , Alex Shi , Mark Rutland Subject: [PATCH 4.9 064/102] arm64: use RET instruction for exiting the trampoline Date: Fri, 6 Apr 2018 15:23:45 +0200 Message-Id: <20180406084340.553370699@linuxfoundation.org> In-Reply-To: <20180406084331.507038179@linuxfoundation.org> References: <20180406084331.507038179@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Will Deacon commit be04a6d1126b upstream. Speculation attacks against the entry trampoline can potentially resteer the speculative instruction stream through the indirect branch and into arbitrary gadgets within the kernel. This patch defends against these attacks by forcing a misprediction through the return stack: a dummy BL instruction loads an entry into the stack, so that the predicted program flow of the subsequent RET instruction is to a branch-to-self instruction which is finally resolved as a branch to the kernel vectors with speculation suppressed. Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas Signed-off-by: Alex Shi [v4.9 backport] Signed-off-by: Mark Rutland [v4.9 backport] Tested-by: Will Deacon Tested-by: Greg Hackmann Signed-off-by: Greg Kroah-Hartman --- arch/arm64/kernel/entry.S | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -880,6 +880,14 @@ __ni_sys_trace: .if \regsize == 64 msr tpidrro_el0, x30 // Restored in kernel_ventry .endif + /* + * Defend against branch aliasing attacks by pushing a dummy + * entry onto the return stack and using a RET instruction to + * enter the full-fat kernel vectors. + */ + bl 2f + b . +2: tramp_map_kernel x30 #ifdef CONFIG_RANDOMIZE_BASE adr x30, tramp_vectors + PAGE_SIZE @@ -892,7 +900,7 @@ __ni_sys_trace: msr vbar_el1, x30 add x30, x30, #(1b - tramp_vectors) isb - br x30 + ret .endm .macro tramp_exit, regsize = 64