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Subject[PATCH v2 2/8] bootconfig: Add bootconfig magic word for indicating bootconfig explicitly
Date
Add bootconfig magic word to the end of bootconfig on initrd
image for indicating explicitly the bootconfig is there.
Also tools/bootconfig treats wrong size or wrong checksum or
parse error as an error, because if there is a bootconfig magic
word, there must be a bootconfig.

The bootconfig magic word is "#BOOTCONFIG\n", 12 bytes word.
Thus the block image of the initrd file with bootconfig is
as follows.

[Initrd][bootconfig][size][csum][#BOOTCONFIG\n]

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
V2: Update Kconfig comment.
---
Documentation/admin-guide/bootconfig.rst | 10 +++++--
include/linux/bootconfig.h | 3 ++
init/Kconfig | 2 +
init/main.c | 6 +++-
tools/bootconfig/main.c | 43 ++++++++++++++++++++++--------
tools/bootconfig/test-bootconfig.sh | 2 +
6 files changed, 49 insertions(+), 17 deletions(-)

diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst
index b342a6796392..5e7609936507 100644
--- a/Documentation/admin-guide/bootconfig.rst
+++ b/Documentation/admin-guide/bootconfig.rst
@@ -102,9 +102,13 @@ Boot Kernel With a Boot Config
==============================

Since the boot configuration file is loaded with initrd, it will be added
-to the end of the initrd (initramfs) image file. The Linux kernel decodes
-the last part of the initrd image in memory to get the boot configuration
-data.
+to the end of the initrd (initramfs) image file with size, checksum and
+12-byte magic word as below.
+
+[initrd][bootconfig][size(u32)][checksum(u32)][#BOOTCONFIG\n]
+
+The Linux kernel decodes the last part of the initrd image in memory to
+get the boot configuration data.
Because of this "piggyback" method, there is no need to change or
update the boot loader and the kernel image itself.

diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
index 7e18c939663e..d11e183fcb54 100644
--- a/include/linux/bootconfig.h
+++ b/include/linux/bootconfig.h
@@ -10,6 +10,9 @@
#include <linux/kernel.h>
#include <linux/types.h>

+#define BOOTCONFIG_MAGIC "#BOOTCONFIG\n"
+#define BOOTCONFIG_MAGIC_LEN 12
+
/* XBC tree node */
struct xbc_node {
u16 next;
diff --git a/init/Kconfig b/init/Kconfig
index e76e9241552c..6ffaf4940f3e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1231,7 +1231,7 @@ config BOOT_CONFIG
Extra boot config allows system admin to pass a config file as
complemental extension of kernel cmdline when booting.
The boot config file must be attached at the end of initramfs
- with checksum and size.
+ with checksum, size and magic word.
See <file:Documentation/admin-guide/bootconfig.rst> for details.

If unsure, say Y.
diff --git a/init/main.c b/init/main.c
index ae4e37681247..fe3ed874c748 100644
--- a/init/main.c
+++ b/init/main.c
@@ -374,7 +374,11 @@ static void __init setup_boot_config(const char *cmdline)
if (!initrd_end)
goto not_found;

- hdr = (u32 *)(initrd_end - 8);
+ data = (char *)initrd_end - BOOTCONFIG_MAGIC_LEN;
+ if (memcmp(data, BOOTCONFIG_MAGIC, BOOTCONFIG_MAGIC_LEN))
+ goto not_found;
+
+ hdr = (u32 *)(data - 8);
size = hdr[0];
csum = hdr[1];

diff --git a/tools/bootconfig/main.c b/tools/bootconfig/main.c
index e18eeb070562..742271f019a9 100644
--- a/tools/bootconfig/main.c
+++ b/tools/bootconfig/main.c
@@ -131,15 +131,26 @@ int load_xbc_from_initrd(int fd, char **buf)
struct stat stat;
int ret;
u32 size = 0, csum = 0, rcsum;
+ char magic[BOOTCONFIG_MAGIC_LEN];

ret = fstat(fd, &stat);
if (ret < 0)
return -errno;

- if (stat.st_size < 8)
+ if (stat.st_size < 8 + BOOTCONFIG_MAGIC_LEN)
return 0;

- if (lseek(fd, -8, SEEK_END) < 0) {
+ if (lseek(fd, -BOOTCONFIG_MAGIC_LEN, SEEK_END) < 0) {
+ pr_err("Failed to lseek: %d\n", -errno);
+ return -errno;
+ }
+ if (read(fd, magic, BOOTCONFIG_MAGIC_LEN) < 0)
+ return -errno;
+ /* Check the bootconfig magic bytes */
+ if (memcmp(magic, BOOTCONFIG_MAGIC, BOOTCONFIG_MAGIC_LEN) != 0)
+ return 0;
+
+ if (lseek(fd, -(8 + BOOTCONFIG_MAGIC_LEN), SEEK_END) < 0) {
pr_err("Failed to lseek: %d\n", -errno);
return -errno;
}
@@ -150,11 +161,14 @@ int load_xbc_from_initrd(int fd, char **buf)
if (read(fd, &csum, sizeof(u32)) < 0)
return -errno;

- /* Wrong size, maybe no boot config here */
- if (stat.st_size < size + 8)
- return 0;
+ /* Wrong size error */
+ if (stat.st_size < size + 8 + BOOTCONFIG_MAGIC_LEN) {
+ pr_err("bootconfig size is too big\n");
+ return -E2BIG;
+ }

- if (lseek(fd, stat.st_size - 8 - size, SEEK_SET) < 0) {
+ if (lseek(fd, stat.st_size - (size + 8 + BOOTCONFIG_MAGIC_LEN),
+ SEEK_SET) < 0) {
pr_err("Failed to lseek: %d\n", -errno);
return -errno;
}
@@ -163,17 +177,17 @@ int load_xbc_from_initrd(int fd, char **buf)
if (ret < 0)
return ret;

- /* Wrong Checksum, maybe no boot config here */
+ /* Wrong Checksum */
rcsum = checksum((unsigned char *)*buf, size);
if (csum != rcsum) {
pr_err("checksum error: %d != %d\n", csum, rcsum);
- return 0;
+ return -EINVAL;
}

ret = xbc_init(*buf);
- /* Wrong data, maybe no boot config here */
+ /* Wrong data */
if (ret < 0)
- return 0;
+ return ret;

return size;
}
@@ -226,7 +240,8 @@ int delete_xbc(const char *path)
} else if (size > 0) {
ret = fstat(fd, &stat);
if (!ret)
- ret = ftruncate(fd, stat.st_size - size - 8);
+ ret = ftruncate(fd, stat.st_size
+ - size - 8 - BOOTCONFIG_MAGIC_LEN);
if (ret)
ret = -errno;
} /* Ignore if there is no boot config in initrd */
@@ -295,6 +310,12 @@ int apply_xbc(const char *path, const char *xbc_path)
pr_err("Failed to apply a boot config: %d\n", ret);
return ret;
}
+ /* Write a magic word of the bootconfig */
+ ret = write(fd, BOOTCONFIG_MAGIC, BOOTCONFIG_MAGIC_LEN);
+ if (ret < 0) {
+ pr_err("Failed to apply a boot config magic: %d\n", ret);
+ return ret;
+ }
close(fd);
free(data);

diff --git a/tools/bootconfig/test-bootconfig.sh b/tools/bootconfig/test-bootconfig.sh
index 1de06de328e2..adafb7c50940 100755
--- a/tools/bootconfig/test-bootconfig.sh
+++ b/tools/bootconfig/test-bootconfig.sh
@@ -49,7 +49,7 @@ xpass $BOOTCONF -a $TEMPCONF $INITRD
new_size=$(stat -c %s $INITRD)

echo "File size check"
-xpass test $new_size -eq $(expr $bconf_size + $initrd_size + 9)
+xpass test $new_size -eq $(expr $bconf_size + $initrd_size + 9 + 12)

echo "Apply command repeat test"
xpass $BOOTCONF -a $TEMPCONF $INITRD
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