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    Subject[RFC][PATCH 5/6] x86, efi: Fix endian issues and unaligned accesses
    Date
    From: Matt Fleming <matt.fleming@intel.com>

    We may need to convert the endianness of the data we read from/write
    to 'buf', so let's use {get,put}_unaligned_le32() to do that. Failure
    to do so can result in accessing invalid memory, leading to a
    segfault. Stephen Rothwell noticed this bug while cross-building an
    x86_64 allmodconfig kernel on PowerPC.

    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 bus
    errors when cross-building an x86 kernel on risc architectures.

    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Nick Bowler <nbowler@elliptictech.com>
    Tested-by: Stephen Rothwell <sfr@canb.auug.org.au>
    Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
    Signed-off-by: Matt Fleming <matt.fleming@intel.com>
    ---
    arch/x86/boot/tools/build.c | 31 +++++++++++++++----------------
    1 files changed, 15 insertions(+), 16 deletions(-)

    diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
    index 4e9bd6b..f2ac95e 100644
    --- a/arch/x86/boot/tools/build.c
    +++ b/arch/x86/boot/tools/build.c
    @@ -34,6 +34,7 @@
    #include <fcntl.h>
    #include <sys/mman.h>
    #include <asm/boot.h>
    +#include <tools/le_byteshift.h>

    typedef unsigned char u8;
    typedef unsigned short u16;
    @@ -41,6 +42,7 @@ typedef unsigned long u32;

    #define DEFAULT_MAJOR_ROOT 0
    #define DEFAULT_MINOR_ROOT 0
    +#define DEFAULT_ROOT_DEV (DEFAULT_MAJOR_ROOT << 8 | DEFAULT_MINOR_ROOT)

    /* Minimal number of setup sectors */
    #define SETUP_SECT_MIN 5
    @@ -159,7 +161,7 @@ int main(int argc, char ** argv)
    die("read-error on `setup'");
    if (c < 1024)
    die("The setup must be at least 1024 bytes");
    - if (buf[510] != 0x55 || buf[511] != 0xaa)
    + if (get_unaligned_le16(&buf[510]) != 0xAA55)
    die("Boot block hasn't got boot flag (0xAA55)");
    fclose(file);

    @@ -171,8 +173,7 @@ int main(int argc, char ** argv)
    memset(buf+c, 0, i-c);

    /* Set the default root device */
    - buf[508] = DEFAULT_MINOR_ROOT;
    - buf[509] = DEFAULT_MAJOR_ROOT;
    + put_unaligned_le16(DEFAULT_ROOT_DEV, &buf[508]);

    fprintf(stderr, "Setup is %d bytes (padded to %d bytes).\n", c, i);

    @@ -192,44 +193,42 @@ 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;
    + put_unaligned_le32(sys_size, &buf[0x1f4]);

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

    - pe_header = *(unsigned int *)&buf[0x3c];
    + pe_header = get_unaligned_le32(&buf[0x3c]);

    /* Size of code */
    - *(unsigned int *)&buf[pe_header + 0x1c] = file_sz;
    + put_unaligned_le32(file_sz, &buf[pe_header + 0x1c]);

    /* Size of image */
    - *(unsigned int *)&buf[pe_header + 0x50] = file_sz;
    + put_unaligned_le32(file_sz, &buf[pe_header + 0x50]);

    #ifdef CONFIG_X86_32
    /* Address of entry point */
    - *(unsigned int *)&buf[pe_header + 0x28] = i;
    + put_unaligned_le32(i, &buf[pe_header + 0x28]);

    /* .text size */
    - *(unsigned int *)&buf[pe_header + 0xb0] = file_sz;
    + put_unaligned_le32(file_sz, &buf[pe_header + 0xb0]);

    /* .text size of initialised data */
    - *(unsigned int *)&buf[pe_header + 0xb8] = file_sz;
    + put_unaligned_le32(file_sz, &buf[pe_header + 0xb8]);
    #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;
    + put_unaligned_le32(i + 512, &buf[pe_header + 0x28]);

    /* .text size */
    - *(unsigned int *)&buf[pe_header + 0xc0] = file_sz;
    + put_unaligned_le32(file_sz, &buf[pe_header + 0xc0]);

    /* .text size of initialised data */
    - *(unsigned int *)&buf[pe_header + 0xc8] = file_sz;
    + put_unaligned_le32(file_sz, &buf[pe_header + 0xc8]);
    +
    #endif /* CONFIG_X86_32 */
    #endif /* CONFIG_EFI_STUB */

    --
    1.7.4.4


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