From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751645AbcEJRzw (ORCPT ); Tue, 10 May 2016 13:55:52 -0400 Received: from mail-pa0-f44.google.com ([209.85.220.44]:34283 "EHLO mail-pa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751076AbcEJRzv (ORCPT ); Tue, 10 May 2016 13:55:51 -0400 Date: Tue, 10 May 2016 10:55:49 -0700 From: Kees Cook To: Catalin Marinas Cc: "Jon Medhurst (Tixy)" , Hector Marco , Nicolas Pitre , Will Deacon , AKASHI Takahiro , Lorenzo Pieralisi , Jisheng Zhang , Mark Rutland , James Morse , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH] arm64: kernel: Fix incorrect brk randomization Message-ID: <20160510175549.GA20496@www.outflux.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This fixes two issues with the arm64 brk randomziation. First, the STACK_RND_MASK was being used incorrectly. The original code was: unsigned long range_end = base + (STACK_RND_MASK << PAGE_SHIFT) + 1; STACK_RND_MASK is 0x7ff (32-bit) or 0x3ffff (64-bit), with 4K pages where PAGE_SHIFT is 12: #define STACK_RND_MASK (test_thread_flag(TIF_32BIT) ? \ 0x7ff >> (PAGE_SHIFT - 12) : \ 0x3ffff >> (PAGE_SHIFT - 12)) This means the resulting offset from base would be 0x7ff0001 or 0x3ffff0001, which is wrong since it creates an unaligned end address. It was likely intended to be: unsigned long range_end = base + ((STACK_RND_MASK + 1) << PAGE_SHIFT) Which would result in offsets of 0x800000 (32-bit) and 0x40000000 (64-bit). However, even this corrected 32-bit compat offset (0x00800000) is much smaller than native ARM's brk randomization value (0x02000000): unsigned long arch_randomize_brk(struct mm_struct *mm) { unsigned long range_end = mm->brk + 0x02000000; return randomize_range(mm->brk, range_end, 0) ? : mm->brk; } So, instead of basing arm64's brk randomization on mistaken STACK_RND_MASK calculations, just use specific corrected values for compat (0x2000000) and native arm64 (0x40000000). Signed-off-by: Kees Cook --- arch/arm64/kernel/process.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 80624829db61..0d0969bcd76d 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -382,13 +382,14 @@ unsigned long arch_align_stack(unsigned long sp) return sp & ~0xf; } -static unsigned long randomize_base(unsigned long base) -{ - unsigned long range_end = base + (STACK_RND_MASK << PAGE_SHIFT) + 1; - return randomize_range(base, range_end, 0) ? : base; -} - unsigned long arch_randomize_brk(struct mm_struct *mm) { - return randomize_base(mm->brk); + unsigned long range_end = mm->brk; + + if (test_thread_flag(TIF_32BIT)) + range_end += 0x02000000; + else + range_end += 0x40000000; + + return randomize_range(mm->brk, range_end, 0) ? : mm->brk; } -- 2.6.3 -- Kees Cook Chrome OS & Brillo Security