From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Biggers Date: Thu, 03 Jan 2019 17:17:00 +0000 Subject: Re: Bug report: unaligned access with ext4 encryption Message-Id: <20190103171659.GA208343@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit List-Id: References: <20181230162906.GI27785@darkstar.musicnaut.iki.fi> In-Reply-To: <20181230162906.GI27785@darkstar.musicnaut.iki.fi> To: Aaro Koskinen , David Howells Cc: "Theodore Y. Ts'o" , Jaegeuk Kim , linux-fscrypt@vger.kernel.org, linux-kernel@vger.kernel.org, keyrings@vger.kernel.org On Sun, Dec 30, 2018 at 06:29:06PM +0200, Aaro Koskinen wrote: > Hi, > > When using ext4 encryption on SPARC, there's plenty of dmesg noise about > unaligned access: > > [ 167.269526] Kernel unaligned access at TPC[5497a0] find_and_lock_process_key+0x80/0x120 > [ 167.270152] Kernel unaligned access at TPC[5497a0] find_and_lock_process_key+0x80/0x120 > [ 181.087451] log_unaligned: 5 callbacks suppressed > [ 181.087511] Kernel unaligned access at TPC[5497a0] find_and_lock_process_key+0x80/0x120 > [ 181.092435] Kernel unaligned access at TPC[5497a0] find_and_lock_process_key+0x80/0x120 > [ 181.095816] Kernel unaligned access at TPC[5497a0] find_and_lock_process_key+0x80/0x120 > > And also seen on an ARM machine: > > $ cat /proc/cpu/alignment > User: 0 > System: 1028193 (find_and_lock_process_key+0x84/0x10c) > Skipped: 0 > Half: 0 > Word: 1028193 > DWord: 0 > Multi: 0 > User faults: 0 (ignored) > > Looks like user_key_payload layout is not optimal when data address > is used for fscrypt_key... I tried the below change and got rid of the > messages. Not sure what the proper fix should be? > > A. > > diff --git a/include/keys/user-type.h b/include/keys/user-type.h > index e098cbe27db5..6495ffcfe510 100644 > --- a/include/keys/user-type.h > +++ b/include/keys/user-type.h > @@ -31,7 +31,7 @@ > struct user_key_payload { > struct rcu_head rcu; /* RCU destructor */ > unsigned short datalen; /* length of this data */ > - char data[0]; /* actual data */ > + char data[0] __aligned(4); /* actual data */ > }; > > extern struct key_type key_type_user; > Hi Aaro, thanks for the bug report! I think you're on the right track; it makes much more sense to have the keyrings subsystem store the payload with better alignment, than to work around the 2-byte alignment in fscrypt. But how about '__aligned(__alignof__(u64))' instead? 4 bytes may not be enough. David, what do you think? - Eric From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:51882 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730554AbfACRRD (ORCPT ); Thu, 3 Jan 2019 12:17:03 -0500 Date: Thu, 3 Jan 2019 09:17:00 -0800 From: Eric Biggers Subject: Re: Bug report: unaligned access with ext4 encryption Message-ID: <20190103171659.GA208343@gmail.com> References: <20181230162906.GI27785@darkstar.musicnaut.iki.fi> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181230162906.GI27785@darkstar.musicnaut.iki.fi> Sender: linux-fscrypt-owner@vger.kernel.org To: Aaro Koskinen , David Howells Cc: "Theodore Y. Ts'o" , Jaegeuk Kim , linux-fscrypt@vger.kernel.org, linux-kernel@vger.kernel.org, keyrings@vger.kernel.org List-ID: On Sun, Dec 30, 2018 at 06:29:06PM +0200, Aaro Koskinen wrote: > Hi, > > When using ext4 encryption on SPARC, there's plenty of dmesg noise about > unaligned access: > > [ 167.269526] Kernel unaligned access at TPC[5497a0] find_and_lock_process_key+0x80/0x120 > [ 167.270152] Kernel unaligned access at TPC[5497a0] find_and_lock_process_key+0x80/0x120 > [ 181.087451] log_unaligned: 5 callbacks suppressed > [ 181.087511] Kernel unaligned access at TPC[5497a0] find_and_lock_process_key+0x80/0x120 > [ 181.092435] Kernel unaligned access at TPC[5497a0] find_and_lock_process_key+0x80/0x120 > [ 181.095816] Kernel unaligned access at TPC[5497a0] find_and_lock_process_key+0x80/0x120 > > And also seen on an ARM machine: > > $ cat /proc/cpu/alignment > User: 0 > System: 1028193 (find_and_lock_process_key+0x84/0x10c) > Skipped: 0 > Half: 0 > Word: 1028193 > DWord: 0 > Multi: 0 > User faults: 0 (ignored) > > Looks like user_key_payload layout is not optimal when data address > is used for fscrypt_key... I tried the below change and got rid of the > messages. Not sure what the proper fix should be? > > A. > > diff --git a/include/keys/user-type.h b/include/keys/user-type.h > index e098cbe27db5..6495ffcfe510 100644 > --- a/include/keys/user-type.h > +++ b/include/keys/user-type.h > @@ -31,7 +31,7 @@ > struct user_key_payload { > struct rcu_head rcu; /* RCU destructor */ > unsigned short datalen; /* length of this data */ > - char data[0]; /* actual data */ > + char data[0] __aligned(4); /* actual data */ > }; > > extern struct key_type key_type_user; > Hi Aaro, thanks for the bug report! I think you're on the right track; it makes much more sense to have the keyrings subsystem store the payload with better alignment, than to work around the 2-byte alignment in fscrypt. But how about '__aligned(__alignof__(u64))' instead? 4 bytes may not be enough. David, what do you think? - Eric