From patchwork Tue Nov 1 18:48:07 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Guilherme G. Piccoli" X-Patchwork-Id: 13027325 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 8CBF3C433FE for ; Tue, 1 Nov 2022 18:48:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230302AbiKASsc (ORCPT ); Tue, 1 Nov 2022 14:48:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58436 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230136AbiKASsb (ORCPT ); Tue, 1 Nov 2022 14:48:31 -0400 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4FD8517E23; Tue, 1 Nov 2022 11:48:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:MIME-Version:Message-Id:Date:Subject: Cc:To:From:Sender:Reply-To:Content-Type:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: In-Reply-To:References:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=KiM8NF3I5HDTZGKG8OKbQBwCPXdwKmsbyN9xYuphi7Y=; b=N1pyzw2l7vEf5w1x4PLENi7pre PsKQZp4roXBXYz4FPYwca1L4/BmSSk7IqfT/hs5lT5iPYtSwsUnxmviA4k0RjMD6BVtNelG+xO+Zv S0hX4hs4+hS+QtuV/dJBi3is1rCy2lkvrdUOleWZOtDWly3t3IYyNlJ3ksmuck9SVMJH8IchEXhfQ B4PXqzl30zZ26srn1JSjxrAJfWzukknBJPXEn0Oh19FKLDWeWlejxf4DDLg1s7pFdbAGUwvWOYLt1 JcVTak1XjXp4Z/PV9wlKhxfOOMCga0xHqKzyXFLZn8rtRTd6wFMKNxou579SA0TfaDgKwUd+OAmwH bq+cDykg==; Received: from [177.102.148.33] (helo=localhost) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_SECP256R1__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1opwJE-00ASTb-ES; Tue, 01 Nov 2022 19:48:25 +0100 From: "Guilherme G. Piccoli" To: linux-hardening@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-efi@vger.kernel.org, kernel-dev@igalia.com, kernel@gpiccoli.net, keescook@chromium.org, anton@enomsg.org, ccross@android.com, tony.luck@intel.com, "Guilherme G. Piccoli" , Ard Biesheuvel Subject: [PATCH V3] efi: pstore: Add module parameter for setting the record size Date: Tue, 1 Nov 2022 15:48:07 -0300 Message-Id: <20221101184808.80747-1-gpiccoli@igalia.com> X-Mailer: git-send-email 2.38.0 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org By default, the efi-pstore backend hardcode the UEFI variable size as 1024 bytes. The historical reasons for that were discussed by Ard in threads [0][1]: "there is some cargo cult from prehistoric EFI times going on here, it seems. Or maybe just misinterpretation of the maximum size for the variable *name* vs the variable itself.". "OVMF has OvmfPkg/OvmfPkgX64.dsc: gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000 OvmfPkg/OvmfPkgX64.dsc: gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x8400 where the first one is without secure boot and the second with secure boot. Interestingly, the default is gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x400 so this is probably where this 1k number comes from." With that, and since there is not such a limit in the UEFI spec, we have the confidence to hereby add a module parameter to enable advanced users to change the UEFI record size for efi-pstore data collection, this way allowing a much easier reading of the collected log, which wouldn't be scattered anymore among many small files. Through empirical analysis we observed that extreme low values (like 8 bytes) could eventually cause writing issues, so given that and the OVMF default discussed, we limited the minimum value to 1024 bytes, which also is still the default. [0] https://lore.kernel.org/lkml/CAMj1kXF4UyRMh2Y_KakeNBHvkHhTtavASTAxXinDO1rhPe_wYg@mail.gmail.com/ [1] https://lore.kernel.org/lkml/CAMj1kXFy-2KddGu+dgebAdU9v2sindxVoiHLWuVhqYw+R=kqng@mail.gmail.com/ Cc: Ard Biesheuvel Signed-off-by: Guilherme G. Piccoli --- V3: - Stick with 1024 to the varname size (thanks Ard!). - Rebased to v6.1-rc3. Hey folks, I've tested multiple record_size values, using lz4, zstd, deflate and no compression. For smaller ones ( up to 4k), all cases worked (for deflate, there was some failures even with 1024, and even with this patch reverted). For bigger sizes, no compression/deflate fails for 8k+, lz4 for values bigger than 16k and zstd only for values more then 20k. I've instrumented the function efivar_set_variable_locked() to get the return value during panic, and when it fails, usually it gives 0x8000000000000002 (EFI_INVALID_PARAMETER it seems?). It's not related to this patch specifically, but worth mentioning in case you have ideas. Thanks, Guilherme drivers/firmware/efi/efi-pstore.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c index 3bddc152fcd4..81ed4fc6d76d 100644 --- a/drivers/firmware/efi/efi-pstore.c +++ b/drivers/firmware/efi/efi-pstore.c @@ -10,7 +10,9 @@ MODULE_IMPORT_NS(EFIVAR); #define DUMP_NAME_LEN 66 -#define EFIVARS_DATA_SIZE_MAX 1024 +static unsigned int record_size = 1024; +module_param(record_size, uint, 0444); +MODULE_PARM_DESC(record_size, "size of each pstore UEFI var (in bytes, min/default=1024)"); static bool efivars_pstore_disable = IS_ENABLED(CONFIG_EFI_VARS_PSTORE_DEFAULT_DISABLE); @@ -30,7 +32,7 @@ static int efi_pstore_open(struct pstore_info *psi) if (err) return err; - psi->data = kzalloc(EFIVARS_DATA_SIZE_MAX, GFP_KERNEL); + psi->data = kzalloc(record_size, GFP_KERNEL); if (!psi->data) return -ENOMEM; @@ -52,7 +54,7 @@ static inline u64 generic_id(u64 timestamp, unsigned int part, int count) static int efi_pstore_read_func(struct pstore_record *record, efi_char16_t *varname) { - unsigned long wlen, size = EFIVARS_DATA_SIZE_MAX; + unsigned long wlen, size = record_size; char name[DUMP_NAME_LEN], data_type; efi_status_t status; int cnt; @@ -133,7 +135,7 @@ static ssize_t efi_pstore_read(struct pstore_record *record) efi_status_t status; for (;;) { - varname_size = EFIVARS_DATA_SIZE_MAX; + varname_size = 1024; /* * If this is the first read() call in the pstore enumeration, @@ -224,11 +226,20 @@ static __init int efivars_pstore_init(void) if (efivars_pstore_disable) return 0; - efi_pstore_info.buf = kmalloc(4096, GFP_KERNEL); + /* + * Notice that 1024 is the minimum here to prevent issues with + * decompression algorithms that were spotted during tests; + * even in the case of not using compression, smaller values would + * just pollute more the pstore FS with many small collected files. + */ + if (record_size < 1024) + record_size = 1024; + + efi_pstore_info.buf = kmalloc(record_size, GFP_KERNEL); if (!efi_pstore_info.buf) return -ENOMEM; - efi_pstore_info.bufsize = 1024; + efi_pstore_info.bufsize = record_size; if (pstore_register(&efi_pstore_info)) { kfree(efi_pstore_info.buf);