Re: [PATCH v7 1/3 RESEND] block:sed-opal: SED Opal keystore

From: Nathan Chancellor <nathan@kernel.org>
To: gjoyce@linux.vnet.ibm.com
Cc: linux-block@vger.kernel.org, axboe@kernel.dk, jarkko@kernel.org,
	linuxppc-dev@lists.ozlabs.org, jonathan.derrick@linux.dev,
	brking@linux.vnet.ibm.com, msuchanek@suse.de, mpe@ellerman.id.au,
	nayna@linux.ibm.com, akpm@linux-foundation.org,
	keyrings@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH v7 1/3 RESEND] block:sed-opal: SED Opal keystore
Date: Wed, 13 Sep 2023 09:56:12 -0700	[thread overview]
Message-ID: <20230913165612.GA2213586@dev-arch.thelio-3990X> (raw)
In-Reply-To: <20230908153056.3503975-2-gjoyce@linux.vnet.ibm.com>

Hi Greg,

On Fri, Sep 08, 2023 at 10:30:54AM -0500, gjoyce@linux.vnet.ibm.com wrote:
> From: Greg Joyce <gjoyce@linux.vnet.ibm.com>
> 
> Add read and write functions that allow SED Opal keys to stored
> in a permanent keystore.
> 
> Signed-off-by: Greg Joyce <gjoyce@linux.vnet.ibm.com>
> Reviewed-by: Jonathan Derrick <jonathan.derrick@linux.dev>
> ---
>  block/Makefile               |  2 +-
>  block/sed-opal-key.c         | 24 ++++++++++++++++++++++++
>  include/linux/sed-opal-key.h | 15 +++++++++++++++
>  3 files changed, 40 insertions(+), 1 deletion(-)
>  create mode 100644 block/sed-opal-key.c
>  create mode 100644 include/linux/sed-opal-key.h
> 
> diff --git a/block/Makefile b/block/Makefile
> index 46ada9dc8bbf..ea07d80402a6 100644
> --- a/block/Makefile
> +++ b/block/Makefile
> @@ -34,7 +34,7 @@ obj-$(CONFIG_BLK_DEV_ZONED)	+= blk-zoned.o
>  obj-$(CONFIG_BLK_WBT)		+= blk-wbt.o
>  obj-$(CONFIG_BLK_DEBUG_FS)	+= blk-mq-debugfs.o
>  obj-$(CONFIG_BLK_DEBUG_FS_ZONED)+= blk-mq-debugfs-zoned.o
> -obj-$(CONFIG_BLK_SED_OPAL)	+= sed-opal.o
> +obj-$(CONFIG_BLK_SED_OPAL)	+= sed-opal.o sed-opal-key.o
>  obj-$(CONFIG_BLK_PM)		+= blk-pm.o
>  obj-$(CONFIG_BLK_INLINE_ENCRYPTION)	+= blk-crypto.o blk-crypto-profile.o \
>  					   blk-crypto-sysfs.o
> diff --git a/block/sed-opal-key.c b/block/sed-opal-key.c
> new file mode 100644
> index 000000000000..16f380164c44
> --- /dev/null
> +++ b/block/sed-opal-key.c
> @@ -0,0 +1,24 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * SED key operations.
> + *
> + * Copyright (C) 2022 IBM Corporation
> + *
> + * These are the accessor functions (read/write) for SED Opal
> + * keys. Specific keystores can provide overrides.
> + *
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/errno.h>
> +#include <linux/sed-opal-key.h>
> +
> +int __weak sed_read_key(char *keyname, char *key, u_int *keylen)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +int __weak sed_write_key(char *keyname, char *key, u_int keylen)
> +{
> +	return -EOPNOTSUPP;
> +}

This change causes a build failure for certain clang configurations due
to an unfortunate issue [1] with recordmcount, clang's integrated
assembler, and object files that contain a section with only weak
functions/symbols (in this case, the .text section in sed-opal-key.c),
resulting in

  Cannot find symbol for section 2: .text.
  block/sed-opal-key.o: failed

when building this file.

Is there any real reason to have a separate translation unit for these
two functions versus just having them living in sed-opal.c? Those two
object files share the same Kconfig dependency. I am happy to send a
patch if that is an acceptable approach.

[1]: https://github.com/ClangBuiltLinux/linux/issues/981

Cheers,
Nathan