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Piccoli" To: linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Cc: 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, ardb@kernel.org, "Guilherme G. Piccoli" Subject: [PATCH V2 3/3] efi: pstore: Add module parameter for setting the record size Date: Thu, 13 Oct 2022 18:06:48 -0300 Message-Id: <20221013210648.137452-4-gpiccoli@igalia.com> X-Mailer: git-send-email 2.38.0 In-Reply-To: <20221013210648.137452-1-gpiccoli@igalia.com> References: <20221013210648.137452-1-gpiccoli@igalia.com> MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1746608422788491564?= X-GMAIL-MSGID: =?utf-8?q?1746608422788491564?= 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 is not 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 --- V2: - Fixed a memory corruption bug in the code (that wasn't causing trouble before due to the fixed sized of record_size), thanks Ard for spotting this! - Added Ard's archeology in the commit message plus a comment with the reasoning behind the minimum value. 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 97a9e84840a0..827e32427ddb 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 = record_size; /* * 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);