linux-kernel - [PATCH 8/8] efi: pstore: Add module parameter for setting the record size

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Date:   Thu,  6 Oct 2022 19:42:12 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc:     kernel-dev@...lia.com, kernel@...ccoli.net, keescook@...omium.org,
        anton@...msg.org, ccross@...roid.com, tony.luck@...el.com,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        linux-efi@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>
Subject: [PATCH 8/8] efi: pstore: Add module parameter for setting the record size

By default, the efi-pstore backend hardcode the UEFI variable size
as 1024 bytes. That's not a big deal, but at the same time having
no way to change that in the kernel is a bit bummer for specialized
users - there is not such a limit in the UEFI specification.

So, add here a module parameter to enable advanced users to change
the UEFI record size for efi-pstore data collection.
Through empirical analysis we observed that extreme low values
(like 8 bytes) could eventually cause writing issues, so we limit
the low end to 1024 bytes (which is also the default).

Cc: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
---
 drivers/firmware/efi/efi-pstore.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
index 97a9e84840a0..78c27f6a83aa 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 +226,14 @@ static __init int efivars_pstore_init(void)
 	if (efivars_pstore_disable)
 		return 0;
 
+	if (record_size < 1024)
+		record_size = 1024;
+
 	efi_pstore_info.buf = kmalloc(4096, 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);
-- 
2.38.0