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Subject[PATCH] x86, efi: Fix unaligned access and endian issues
Date
From: Matt Fleming <matt.fleming@intel.com>

We need to read from and write to 'buf' a byte at a time otherwise
it's possible we'll perform an unaligned access, which can lead to a
segfault when cross-building an x86 kernel on risc architectures.

Also, we may need to convert the endianness of the data we read
from/write to buf, so let's add some helper functions to do that.

Stephen Rothwell noticed this bug when he hit a segfault while
cross-building an x86_64 allmodconfig kernel on PowerPC.

Cc: H. Peter Anvin <hpa@zytor.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
---
arch/x86/boot/tools/build.c | 44 ++++++++++++++++++++++++++++++------------
1 files changed, 31 insertions(+), 13 deletions(-)
diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
index 4e9bd6b..4030cb7 100644
--- a/arch/x86/boot/tools/build.c
+++ b/arch/x86/boot/tools/build.c
@@ -133,6 +133,26 @@ static void usage(void)
die("Usage: build setup system [> image]");
}

+static inline u32 read32_le(u8 *src)
+{
+ u32 data;
+
+ data = *src++;
+ data |= *src++ << 8;
+ data |= *src++ << 16;
+ data |= *src++ << 24;
+
+ return data;
+}
+
+static inline void write32_le(u8 *dst, u32 data)
+{
+ *dst++ = data;
+ *dst++ = data >> 8;
+ *dst++ = data >> 16;
+ *dst++ = data >> 24;
+}
+
int main(int argc, char ** argv)
{
#ifdef CONFIG_EFI_STUB
@@ -192,44 +212,42 @@ int main(int argc, char ** argv)

/* Patch the setup code with the appropriate size parameters */
buf[0x1f1] = setup_sectors-1;
- buf[0x1f4] = sys_size;
- buf[0x1f5] = sys_size >> 8;
- buf[0x1f6] = sys_size >> 16;
- buf[0x1f7] = sys_size >> 24;
+ write32_le(&buf[0x1f4], sys_size);

#ifdef CONFIG_EFI_STUB
file_sz = sz + i + ((sys_size * 16) - sz);

- pe_header = *(unsigned int *)&buf[0x3c];
+ pe_header = read32_le(&buf[0x3c]);

/* Size of code */
- *(unsigned int *)&buf[pe_header + 0x1c] = file_sz;
+ write32_le(&buf[pe_header + 0x1c], file_sz);

/* Size of image */
- *(unsigned int *)&buf[pe_header + 0x50] = file_sz;
+ write32_le(&buf[pe_header + 0x50], file_sz);

#ifdef CONFIG_X86_32
/* Address of entry point */
- *(unsigned int *)&buf[pe_header + 0x28] = i;
+ write32_le(&buf[pe_header + 0x28], i);

/* .text size */
- *(unsigned int *)&buf[pe_header + 0xb0] = file_sz;
+ write32_le(&buf[pe_header + 0xb0], file_sz);

/* .text size of initialised data */
- *(unsigned int *)&buf[pe_header + 0xb8] = file_sz;
+ write32_le(&buf[pe_header + 0xb8], file_sz);
#else
/*
* Address of entry point. startup_32 is at the beginning and
* the 64-bit entry point (startup_64) is always 512 bytes
* after.
*/
- *(unsigned int *)&buf[pe_header + 0x28] = i + 512;
+ write32_le(&buf[pe_header + 0x28], i + 512);

/* .text size */
- *(unsigned int *)&buf[pe_header + 0xc0] = file_sz;
+ write32_le(&buf[pe_header + 0xc0], file_sz);

/* .text size of initialised data */
- *(unsigned int *)&buf[pe_header + 0xc8] = file_sz;
+ write32_le(&buf[pe_header + 0xc8], file_sz);
+
#endif /* CONFIG_X86_32 */
#endif /* CONFIG_EFI_STUB */

--
1.7.4.4


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