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bootconfig: Fix unaligned access when building footer

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Currently we add padding between the bootconfig text and footer to
ensure that the footer is aligned within the initramfs image.
However, because only the bootconfig data is held in memory, not the
full initramfs image, the footer may not be naturally aligned in
memory.

This can result in an alignment fault (SIGBUS) when writing the footer
on some architectures, such as sparc.

Build the footer in a struct on the stack before adding it to the
buffer.

References: https://buildd.debian.org/status/fetch.php?pkg=linux&arch=sparc64&ver=6.16%7Erc7-1%7Eexp1&stamp=1753209801&raw=0
Link: https://lore.kernel.org/all/aIC-NTw-cdm9ZGFw@decadent.org.uk/

Signed-off-by: Ben Hutchings <benh@debian.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
This commit is contained in:
Ben Hutchings 2025-07-23 12:49:25 +02:00 committed by Masami Hiramatsu (Google)
parent 9afa2e0d42
commit 6ed5e20466
1 changed files with 13 additions and 11 deletions
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24
tools/bootconfig/main.c
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@ -11,6 +11,7 @@
#include <string.h>
#include <errno.h>
#include <endian.h>
#include <assert.h>
#include <linux/bootconfig.h>
@ -363,7 +364,12 @@ static int delete_xbc(const char *path)
static int apply_xbc(const char *path, const char *xbc_path)
{
char *buf, *data, *p;
struct {
uint32_t size;
uint32_t csum;
char magic[BOOTCONFIG_MAGIC_LEN];
} footer;
char *buf, *data;
size_t total_size;
struct stat stat;
const char *msg;
@ -433,17 +439,13 @@ static int apply_xbc(const char *path, const char *xbc_path)
size += pad;
/* Add a footer */
p = data + size;
*(uint32_t *)p = htole32(size);
p += sizeof(uint32_t);
footer.size = htole32(size);
footer.csum = htole32(csum);
memcpy(footer.magic, BOOTCONFIG_MAGIC, BOOTCONFIG_MAGIC_LEN);
static_assert(sizeof(footer) == BOOTCONFIG_FOOTER_SIZE);
memcpy(data + size, &footer, BOOTCONFIG_FOOTER_SIZE);
*(uint32_t *)p = htole32(csum);
p += sizeof(uint32_t);
memcpy(p, BOOTCONFIG_MAGIC, BOOTCONFIG_MAGIC_LEN);
p += BOOTCONFIG_MAGIC_LEN;
total_size = p - data;
total_size = size + BOOTCONFIG_FOOTER_SIZE;
ret = write(fd, data, total_size);
if (ret < total_size) {