From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 398E9CCA47E for ; Fri, 3 Jun 2022 18:11:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347888AbiFCSLQ (ORCPT ); Fri, 3 Jun 2022 14:11:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50708 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345998AbiFCR5m (ORCPT ); Fri, 3 Jun 2022 13:57:42 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6B23A222A5; Fri, 3 Jun 2022 10:54:25 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id C8884CE247C; Fri, 3 Jun 2022 17:54:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 93E5AC385A9; Fri, 3 Jun 2022 17:54:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1654278862; bh=CrskhCGudGloMsjS6L0WZPfEK9Z6nD6+NYPtc/n9nTA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UxAvskvl9ucuTj8Tompsh9LcHdRlSht+DXi1D2IAckZoEGnjeNn8Wu52J9m7+Q5ZR ESyFxhxaP1EpFEmXWepIPBM++cB4i5t4tpxs6Bp4Cb6htlXqHjrPrri/qtnqAH0T1E BCXeM+Jh01h8bI65aQpEfyokrBQ4kVRIB1hKvlh4= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mikulas Patocka , Milan Broz , Mike Snitzer Subject: [PATCH 5.17 50/75] dm crypt: make printing of the key constant-time Date: Fri, 3 Jun 2022 19:43:34 +0200 Message-Id: <20220603173823.164330819@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220603173821.749019262@linuxfoundation.org> References: <20220603173821.749019262@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Mikulas Patocka commit 567dd8f34560fa221a6343729474536aa7ede4fd upstream. The device mapper dm-crypt target is using scnprintf("%02x", cc->key[i]) to report the current key to userspace. However, this is not a constant-time operation and it may leak information about the key via timing, via cache access patterns or via the branch predictor. Change dm-crypt's key printing to use "%c" instead of "%02x". Also introduce hex2asc() that carefully avoids any branching or memory accesses when converting a number in the range 0 ... 15 to an ascii character. Cc: stable@vger.kernel.org Signed-off-by: Mikulas Patocka Tested-by: Milan Broz Signed-off-by: Mike Snitzer Signed-off-by: Greg Kroah-Hartman --- drivers/md/dm-crypt.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) --- a/drivers/md/dm-crypt.c +++ b/drivers/md/dm-crypt.c @@ -3449,6 +3449,11 @@ static int crypt_map(struct dm_target *t return DM_MAPIO_SUBMITTED; } +static char hex2asc(unsigned char c) +{ + return c + '0' + ((unsigned)(9 - c) >> 4 & 0x27); +} + static void crypt_status(struct dm_target *ti, status_type_t type, unsigned status_flags, char *result, unsigned maxlen) { @@ -3467,9 +3472,12 @@ static void crypt_status(struct dm_targe if (cc->key_size > 0) { if (cc->key_string) DMEMIT(":%u:%s", cc->key_size, cc->key_string); - else - for (i = 0; i < cc->key_size; i++) - DMEMIT("%02x", cc->key[i]); + else { + for (i = 0; i < cc->key_size; i++) { + DMEMIT("%c%c", hex2asc(cc->key[i] >> 4), + hex2asc(cc->key[i] & 0xf)); + } + } } else DMEMIT("-");