Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759189AbdCVMRU (ORCPT ); Wed, 22 Mar 2017 08:17:20 -0400 Received: from mail-it0-f48.google.com ([209.85.214.48]:36610 "EHLO mail-it0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751590AbdCVMRG (ORCPT ); Wed, 22 Mar 2017 08:17:06 -0400 MIME-Version: 1.0 In-Reply-To: <1490182705-14243-1-git-send-email-sramana@codeaurora.org> References: <904FACBF-3DFE-4DDE-ACB5-7109A137D477@linaro.org> <1490182705-14243-1-git-send-email-sramana@codeaurora.org> From: Ard Biesheuvel Date: Wed, 22 Mar 2017 12:16:24 +0000 Message-ID: Subject: Re: [PATCH v2] arm64: kaslr: Fix up the kernel image alignment To: Srinivas Ramana Cc: Catalin Marinas , Will Deacon , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , linux-arm-msm@vger.kernel.org, Neeraj Upadhyay Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3520 Lines: 82 On 22 March 2017 at 11:38, Srinivas Ramana wrote: > From: Neeraj Upadhyay > > If kernel image extends across alignment boundary, existing > code increases the KASLR offset by size of kernel image. The > offset is masked after resizing. There are cases, where after > masking, we may still have kernel image extending across > boundary. This eventually results in only 2MB block getting > mapped while creating the page tables. This results in data aborts > while accessing unmapped regions during second relocation (with > kaslr offset) in __primary_switch. To fix this problem, round up the > kernel image size, by swapper block size, before adding it for > correction. > > For example consider below case, where kernel image still crosses > 1GB alignment boundary, after masking the offset, which is fixed > by rounding up kernel image size. > > SWAPPER_TABLE_SHIFT = 30 > Swapper using section maps with section size 2MB. > CONFIG_PGTABLE_LEVELS = 3 > VA_BITS = 39 > > _text : 0xffffff8008080000 > _end : 0xffffff800aa1b000 > offset : 0x1f35600000 > mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1) > > (_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7c > (_end + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7d > > offset after existing correction (before mask) = 0x1f37f9b000 > (_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7d > (_end + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7d > > offset (after mask) = 0x1f37e00000 > (_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7c > (_end + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7d > > new offset w/ rounding up = 0x1f38000000 > (_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7d > (_end + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7d > > Fixes: f80fb3a3d508 ("arm64: add support for kernel ASLR") > Signed-off-by: Neeraj Upadhyay > Signed-off-by: Srinivas Ramana Reviewed-by: Ard Biesheuvel ... and thanks for the excellent commit log message! > --- > arch/arm64/kernel/kaslr.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c > index 769f24ef628c..d7e90d97f5c4 100644 > --- a/arch/arm64/kernel/kaslr.c > +++ b/arch/arm64/kernel/kaslr.c > @@ -131,11 +131,15 @@ u64 __init kaslr_early_init(u64 dt_phys, u64 modulo_offset) > /* > * The kernel Image should not extend across a 1GB/32MB/512MB alignment > * boundary (for 4KB/16KB/64KB granule kernels, respectively). If this > - * happens, increase the KASLR offset by the size of the kernel image. > + * happens, increase the KASLR offset by the size of the kernel image > + * rounded up by SWAPPER_BLOCK_SIZE. > */ > if ((((u64)_text + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT) != > - (((u64)_end + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT)) > - offset = (offset + (u64)(_end - _text)) & mask; > + (((u64)_end + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT)) { > + u64 kimg_sz = _end - _text; > + offset = (offset + round_up(kimg_sz, SWAPPER_BLOCK_SIZE)) > + & mask; > + } > > if (IS_ENABLED(CONFIG_KASAN)) > /* > -- > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc., > is a member of Code Aurora Forum, a Linux Foundation Collaborative Project. >