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

Guilherme G. Piccoli
2022-10-06T22:45:15Z

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@kernel.org>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.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