From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="Yxvzotlq" Received: from smtp-fw-80006.amazon.com (smtp-fw-80006.amazon.com [99.78.197.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E65ACD5C; Wed, 6 Dec 2023 13:33:27 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1701898408; x=1733434408; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=olXMY6IT8d9dmgacsnRgFeTZm0WgXJ1U7yVx5NNY3To=; b=YxvzotlqmijvJgPVVPwxfkQbUystmXG3eLx/7xmblqPL4tGk6E3KCrU8 JvuqXH2aDvDVhsVM0EnYOYjFvWpinKe4sP8HCtVMrC3HG7SJBbhrOGU9X HfRPRyI3681O3GRWMnMgLRdwyZA6RUyTqsI/VC3Hur4Gydyq3kNxgX6nj s=; X-IronPort-AV: E=Sophos;i="6.04,256,1695686400"; d="scan'208";a="257298916" Received: from pdx4-co-svc-p1-lb2-vlan3.amazon.com (HELO email-inbound-relay-pdx-2b-m6i4x-ed19f671.us-west-2.amazon.com) ([10.25.36.214]) by smtp-border-fw-80006.pdx80.corp.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Dec 2023 21:33:28 +0000 Received: from smtpout.prod.us-west-2.prod.farcaster.email.amazon.dev (pdx2-ws-svc-p26-lb5-vlan3.pdx.amazon.com [10.39.38.70]) by email-inbound-relay-pdx-2b-m6i4x-ed19f671.us-west-2.amazon.com (Postfix) with ESMTPS id 32CEA82660; Wed, 6 Dec 2023 21:33:27 +0000 (UTC) Received: from EX19MTAUWA002.ant.amazon.com [10.0.7.35:14806] by smtpin.naws.us-west-2.prod.farcaster.email.amazon.dev [10.0.56.214:2525] with esmtp (Farcaster) id 9e65d653-7053-45d0-8def-e5b76986597e; Wed, 6 Dec 2023 21:33:26 +0000 (UTC) X-Farcaster-Flow-ID: 9e65d653-7053-45d0-8def-e5b76986597e Received: from EX19D020UWC004.ant.amazon.com (10.13.138.149) by EX19MTAUWA002.ant.amazon.com (10.250.64.202) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.40; Wed, 6 Dec 2023 21:33:26 +0000 Received: from dev-dsk-graf-1a-5ce218e4.eu-west-1.amazon.com (10.253.83.51) by EX19D020UWC004.ant.amazon.com (10.13.138.149) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.40; Wed, 6 Dec 2023 21:33:25 +0000 From: Alexander Graf To: CC: , Andrew Morton , Jonathan Corbet , Greg Kroah-Hartman , =?UTF-8?q?Jan=20H=20=2E=20Sch=C3=B6nherr?= , James Gowans Subject: [PATCH v2] initramfs: Expose retained initrd as sysfs file Date: Wed, 6 Dec 2023 21:33:23 +0000 Message-ID: <20231206213323.78233-1-graf@amazon.com> X-Mailer: git-send-email 2.40.1 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: EX19D036UWB004.ant.amazon.com (10.13.139.170) To EX19D020UWC004.ant.amazon.com (10.13.138.149) Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit When the kernel command line option "retain_initrd" is set, we do not free the initrd memory. However, we also don't expose it to anyone for consumption. That leaves us in a weird situation where the only user of this feature is ppc64 and arm64 specific kexec tooling. To make it more generally useful, this patch adds a kobject to the firmware object that contains the initrd context when "retain_initrd" is set. That way, we can access the initrd any time after boot from user space and for example hand it into kexec as --initrd parameter if we want to reboot the same initrd. Or inspect it directly locally. With this patch applied, there is a new /sys/firmware/initrd file when the kernel was booted with an initrd and "retain_initrd" command line option is set. Signed-off-by: Alexander Graf --- v1 -> v2: - Reword commit message to explain the new file path - Add a Documentation/ABI/testing/sysfs-firmware-initrd file --- .../ABI/testing/sysfs-firmware-initrd | 8 ++++++++ .../admin-guide/kernel-parameters.txt | 5 +++-- init/initramfs.c | 18 +++++++++++++++++- 3 files changed, 28 insertions(+), 3 deletions(-) create mode 100644 Documentation/ABI/testing/sysfs-firmware-initrd diff --git a/Documentation/ABI/testing/sysfs-firmware-initrd b/Documentation/ABI/testing/sysfs-firmware-initrd new file mode 100644 index 000000000000..20bf7cf77a19 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-firmware-initrd @@ -0,0 +1,8 @@ +What: /sys/firmware/initrd +Date: December 2023 +Contact: Alexander Graf +Description: + When the kernel was booted with an initrd and the + "retain_initrd" option is set on the kernel command + line, /sys/firmware/initrd contains the contents of the + initrd that the kernel was booted with. diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 65731b060e3f..51575cd31741 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2438,7 +2438,7 @@ between unregistering the boot console and initializing the real console. - keepinitrd [HW,ARM] + keepinitrd [HW,ARM] See retain_initrd. kernelcore= [KNL,X86,IA-64,PPC] Format: nn[KMGTPE] | nn% | "mirror" @@ -5580,7 +5580,8 @@ Useful for devices that are detected asynchronously (e.g. USB and MMC devices). - retain_initrd [RAM] Keep initrd memory after extraction + retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will + be accessible via /sys/firmware/initrd. retbleed= [X86] Control mitigation of RETBleed (Arbitrary Speculative Code Execution with Return Instructions) diff --git a/init/initramfs.c b/init/initramfs.c index 8d0fd946cdd2..25244e2a5739 100644 --- a/init/initramfs.c +++ b/init/initramfs.c @@ -574,6 +574,16 @@ extern unsigned long __initramfs_size; #include #include +static ssize_t raw_read(struct file *file, struct kobject *kobj, + struct bin_attribute *attr, char *buf, + loff_t pos, size_t count) +{ + memcpy(buf, attr->private + pos, count); + return count; +} + +static BIN_ATTR(initrd, 0440, raw_read, NULL, 0); + void __init reserve_initrd_mem(void) { phys_addr_t start; @@ -715,8 +725,14 @@ static void __init do_populate_rootfs(void *unused, async_cookie_t cookie) * If the initrd region is overlapped with crashkernel reserved region, * free only memory that is not part of crashkernel region. */ - if (!do_retain_initrd && initrd_start && !kexec_free_initrd()) + if (!do_retain_initrd && initrd_start && !kexec_free_initrd()) { free_initrd_mem(initrd_start, initrd_end); + } else if (do_retain_initrd) { + bin_attr_initrd.size = initrd_end - initrd_start; + bin_attr_initrd.private = (void *)initrd_start; + if (sysfs_create_bin_file(firmware_kobj, &bin_attr_initrd)) + pr_err("Failed to create initrd sysfs file"); + } initrd_start = 0; initrd_end = 0; -- 2.40.1 Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879