Subject: [PATCH] soc: fsl: qe: Replace one-element array and use struct_size() helper

From: "Gustavo A. R. Silva" <[email-masked]>
Date: Mon, 18 May 2020 17:19:04 -0500

The current codebase makes use of one-element arrays in the following
form:

struct something {
    int length;
    u8 data[1];
};

struct something *instance;

instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
instance->length = size;
memcpy(instance->data, source, size);

but the preferred mechanism to declare variable-length types such as
these ones is a flexible array member[1][2], introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on. So, replace
the one-element array with a flexible-array member.

Also, make use of the new struct_size() helper to properly calculate the
size of struct qe_firmware.

This issue was found with the help of Coccinelle and, audited and fixed
_manually_.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <[email-masked]>
---
 drivers/soc/fsl/qe/qe.c | 4 ++--
 include/soc/fsl/qe/qe.h | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/soc/fsl/qe/qe.c b/drivers/soc/fsl/qe/qe.c
index 447146861c2c1..2df20d6f85fa4 100644
--- a/drivers/soc/fsl/qe/qe.c
+++ b/drivers/soc/fsl/qe/qe.c
@@ -448,7 +448,7 @@ int qe_upload_firmware(const struct qe_firmware *firmware)
 	unsigned int i;
 	unsigned int j;
 	u32 crc;
-	size_t calc_size = sizeof(struct qe_firmware);
+	size_t calc_size;
 	size_t length;
 	const struct qe_header *hdr;
 
@@ -480,7 +480,7 @@ int qe_upload_firmware(const struct qe_firmware *firmware)
 	}
 
 	/* Validate the length and check if there's a CRC */
-	calc_size += (firmware->count - 1) * sizeof(struct qe_microcode);
+	calc_size = struct_size(firmware, microcode, firmware->count);
 
 	for (i = 0; i < firmware->count; i++)
 		/*
diff --git a/include/soc/fsl/qe/qe.h b/include/soc/fsl/qe/qe.h
index e282ac01ec081..3feddfec9f87d 100644
--- a/include/soc/fsl/qe/qe.h
+++ b/include/soc/fsl/qe/qe.h
@@ -307,7 +307,7 @@ struct qe_firmware {
 		u8 revision;		/* The microcode version revision */
 		u8 padding;		/* Reserved, for alignment */
 		u8 reserved[4];		/* Reserved, for future expansion */
-	} __attribute__ ((packed)) microcode[1];
+	} __packed microcode[];
 	/* All microcode binaries should be located here */
 	/* CRC32 should be located here, after the microcode binaries */
 } __attribute__ ((packed));
-- 
2.26.2

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