[PATCH v2] mtd: otp: Put factory OTP/NVRAM into the entropy pool
Linus Walleij
linus.walleij at linaro.org
Sat Jun 3 11:31:59 PDT 2023
The factory OTP, if supported, contains factory-programmed
information such as typically the serial number or production
week for the chip.
As this is device-unique information, submit it into the
system entropy pool.
This does not count as improvement of the entropy as such
but in practice it makes it a bit more random to mix in these
numbers.
Cc: Michael Walle <michael at walle.cc>
Acked-by: Jason A. Donenfeld <Jason at zx2c4.com>
Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
---
ChangeLog v1->v2:
- Drop the conditional to return as many bytes as requested
to add the OTP to the entropy pool: it doesn't matter
whatsoever in this case.
- Collected Jason's ACK.
This is similar to the patch I made to add MMC/SD-card serial
numbers to randomness, just with raw NOR flash.
---
drivers/mtd/mtdcore.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 60670b2f70b9..d03412a82549 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -23,6 +23,7 @@
#include <linux/idr.h>
#include <linux/backing-dev.h>
#include <linux/gfp.h>
+#include <linux/random.h>
#include <linux/slab.h>
#include <linux/reboot.h>
#include <linux/leds.h>
@@ -966,6 +967,24 @@ static int mtd_otp_nvmem_add(struct mtd_info *mtd)
}
if (size > 0) {
+ /*
+ * The factory OTP contains thing such as a unique serial
+ * number and is small, so let's read it out and put it
+ * into the entropy pool.
+ */
+ void *otp;
+
+ otp = kmalloc(size, GFP_KERNEL);
+ if (!otp)
+ return -ENOMEM;
+ err = mtd_nvmem_fact_otp_reg_read(mtd, 0, otp, size);
+ if (err < 0) {
+ kfree(otp);
+ return err;
+ }
+ add_device_randomness(otp, size);
+ kfree(otp);
+
nvmem = mtd_otp_nvmem_register(mtd, "factory-otp", size,
mtd_nvmem_fact_otp_reg_read);
if (IS_ERR(nvmem)) {
--
2.40.1
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