Re: [PATCH] x86: add a crc32 checksum to the kernel image.
From: Ian Campbell
Date: Fri Feb 01 2008 - 04:03:47 EST
On Thu, 2008-01-31 at 14:10 -0800, H. Peter Anvin wrote:
> Hm. I have some minor concerns about this:
>
> * The classical length field is only available in multiples of 16 (I
> realize your patches change that to some degree, but I'd hate to make
> the guarantee that the image payload is the last thing in the image --
> it loses flexibility for the future.) The end of the image isn't
> available in all cases, so this would require padding it out to a
> 16-byte boundary before appending the CRC32. An mmap is guaranteed to
> be zero-padded out to the next page boundary, so explicitly rounding sz
> up (instead of when calculating sys_size) should do the job.
Peter in a followup mail:
> Thinking about this more carefully, we should probably have it rounded
> up to a 16-byte boundary *including* the CRC32, so the CRC32 is
> included in the notional image.
Agreed.
Peter in the first mail again:
> * I believe it is recommended to store the inverse of the crc32, not the
> crc32 itself - it catches more errors. This is also the reason to start
> out with ~0 rather than 0.
If you store the inverted checksum then the complete file will always
sum to 0xdebb20e3 rather than zero.
However I'm told that inverting the checksum only protects extra zeroes
after the CRC. Given that we checksum over a known length and don't
especially care about trailing zeroes in any case I think it is nicer if
the file checksums to zero.
> * Please don't use "unsigned long" to represent a 32-bit number.
Fixed.
---
>From 1c614383dc9cb0c7791ebab386dc012db336b28c Mon Sep 17 00:00:00 2001
From: Ian Campbell <ijc@xxxxxxxxxxxxxx>
Date: Fri, 1 Feb 2008 09:01:22 +0000
Subject: [PATCH] x86: add a crc32 checksum to the kernel image.
Signed-off-by: Ian Campbell <ijc@xxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
---
Documentation/i386/boot.txt | 7 +++
arch/x86/boot/tools/build.c | 88 ++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 94 insertions(+), 1 deletions(-)
diff --git a/Documentation/i386/boot.txt b/Documentation/i386/boot.txt
index b5f5ba1..f853d49 100644
--- a/Documentation/i386/boot.txt
+++ b/Documentation/i386/boot.txt
@@ -531,6 +531,13 @@ Protocol: 2.08+
The length of the compressed payload.
+**** THE IMAGE CHECKSUM
+
+The CRC-32 is calculated over the entire file using an initial
+remainder of 0xffffffff. The checksum is appended to the file
+therefore the CRC of the file up to the limit specified in the syssize
+field of the header is always 0.
+
**** THE KERNEL COMMAND LINE
The kernel command line has become an important way for the boot
diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
index b424874..2ba22e8 100644
--- a/arch/x86/boot/tools/build.c
+++ b/arch/x86/boot/tools/build.c
@@ -50,6 +50,75 @@ typedef unsigned long u32;
u8 buf[SETUP_SECT_MAX*512];
int is_big_kernel;
+/*----------------------------------------------------------------------*/
+
+static const unsigned int crctab32[] = {
+ 0x00000000U, 0x77073096U, 0xee0e612cU, 0x990951baU, 0x076dc419U,
+ 0x706af48fU, 0xe963a535U, 0x9e6495a3U, 0x0edb8832U, 0x79dcb8a4U,
+ 0xe0d5e91eU, 0x97d2d988U, 0x09b64c2bU, 0x7eb17cbdU, 0xe7b82d07U,
+ 0x90bf1d91U, 0x1db71064U, 0x6ab020f2U, 0xf3b97148U, 0x84be41deU,
+ 0x1adad47dU, 0x6ddde4ebU, 0xf4d4b551U, 0x83d385c7U, 0x136c9856U,
+ 0x646ba8c0U, 0xfd62f97aU, 0x8a65c9ecU, 0x14015c4fU, 0x63066cd9U,
+ 0xfa0f3d63U, 0x8d080df5U, 0x3b6e20c8U, 0x4c69105eU, 0xd56041e4U,
+ 0xa2677172U, 0x3c03e4d1U, 0x4b04d447U, 0xd20d85fdU, 0xa50ab56bU,
+ 0x35b5a8faU, 0x42b2986cU, 0xdbbbc9d6U, 0xacbcf940U, 0x32d86ce3U,
+ 0x45df5c75U, 0xdcd60dcfU, 0xabd13d59U, 0x26d930acU, 0x51de003aU,
+ 0xc8d75180U, 0xbfd06116U, 0x21b4f4b5U, 0x56b3c423U, 0xcfba9599U,
+ 0xb8bda50fU, 0x2802b89eU, 0x5f058808U, 0xc60cd9b2U, 0xb10be924U,
+ 0x2f6f7c87U, 0x58684c11U, 0xc1611dabU, 0xb6662d3dU, 0x76dc4190U,
+ 0x01db7106U, 0x98d220bcU, 0xefd5102aU, 0x71b18589U, 0x06b6b51fU,
+ 0x9fbfe4a5U, 0xe8b8d433U, 0x7807c9a2U, 0x0f00f934U, 0x9609a88eU,
+ 0xe10e9818U, 0x7f6a0dbbU, 0x086d3d2dU, 0x91646c97U, 0xe6635c01U,
+ 0x6b6b51f4U, 0x1c6c6162U, 0x856530d8U, 0xf262004eU, 0x6c0695edU,
+ 0x1b01a57bU, 0x8208f4c1U, 0xf50fc457U, 0x65b0d9c6U, 0x12b7e950U,
+ 0x8bbeb8eaU, 0xfcb9887cU, 0x62dd1ddfU, 0x15da2d49U, 0x8cd37cf3U,
+ 0xfbd44c65U, 0x4db26158U, 0x3ab551ceU, 0xa3bc0074U, 0xd4bb30e2U,
+ 0x4adfa541U, 0x3dd895d7U, 0xa4d1c46dU, 0xd3d6f4fbU, 0x4369e96aU,
+ 0x346ed9fcU, 0xad678846U, 0xda60b8d0U, 0x44042d73U, 0x33031de5U,
+ 0xaa0a4c5fU, 0xdd0d7cc9U, 0x5005713cU, 0x270241aaU, 0xbe0b1010U,
+ 0xc90c2086U, 0x5768b525U, 0x206f85b3U, 0xb966d409U, 0xce61e49fU,
+ 0x5edef90eU, 0x29d9c998U, 0xb0d09822U, 0xc7d7a8b4U, 0x59b33d17U,
+ 0x2eb40d81U, 0xb7bd5c3bU, 0xc0ba6cadU, 0xedb88320U, 0x9abfb3b6U,
+ 0x03b6e20cU, 0x74b1d29aU, 0xead54739U, 0x9dd277afU, 0x04db2615U,
+ 0x73dc1683U, 0xe3630b12U, 0x94643b84U, 0x0d6d6a3eU, 0x7a6a5aa8U,
+ 0xe40ecf0bU, 0x9309ff9dU, 0x0a00ae27U, 0x7d079eb1U, 0xf00f9344U,
+ 0x8708a3d2U, 0x1e01f268U, 0x6906c2feU, 0xf762575dU, 0x806567cbU,
+ 0x196c3671U, 0x6e6b06e7U, 0xfed41b76U, 0x89d32be0U, 0x10da7a5aU,
+ 0x67dd4accU, 0xf9b9df6fU, 0x8ebeeff9U, 0x17b7be43U, 0x60b08ed5U,
+ 0xd6d6a3e8U, 0xa1d1937eU, 0x38d8c2c4U, 0x4fdff252U, 0xd1bb67f1U,
+ 0xa6bc5767U, 0x3fb506ddU, 0x48b2364bU, 0xd80d2bdaU, 0xaf0a1b4cU,
+ 0x36034af6U, 0x41047a60U, 0xdf60efc3U, 0xa867df55U, 0x316e8eefU,
+ 0x4669be79U, 0xcb61b38cU, 0xbc66831aU, 0x256fd2a0U, 0x5268e236U,
+ 0xcc0c7795U, 0xbb0b4703U, 0x220216b9U, 0x5505262fU, 0xc5ba3bbeU,
+ 0xb2bd0b28U, 0x2bb45a92U, 0x5cb36a04U, 0xc2d7ffa7U, 0xb5d0cf31U,
+ 0x2cd99e8bU, 0x5bdeae1dU, 0x9b64c2b0U, 0xec63f226U, 0x756aa39cU,
+ 0x026d930aU, 0x9c0906a9U, 0xeb0e363fU, 0x72076785U, 0x05005713U,
+ 0x95bf4a82U, 0xe2b87a14U, 0x7bb12baeU, 0x0cb61b38U, 0x92d28e9bU,
+ 0xe5d5be0dU, 0x7cdcefb7U, 0x0bdbdf21U, 0x86d3d2d4U, 0xf1d4e242U,
+ 0x68ddb3f8U, 0x1fda836eU, 0x81be16cdU, 0xf6b9265bU, 0x6fb077e1U,
+ 0x18b74777U, 0x88085ae6U, 0xff0f6a70U, 0x66063bcaU, 0x11010b5cU,
+ 0x8f659effU, 0xf862ae69U, 0x616bffd3U, 0x166ccf45U, 0xa00ae278U,
+ 0xd70dd2eeU, 0x4e048354U, 0x3903b3c2U, 0xa7672661U, 0xd06016f7U,
+ 0x4969474dU, 0x3e6e77dbU, 0xaed16a4aU, 0xd9d65adcU, 0x40df0b66U,
+ 0x37d83bf0U, 0xa9bcae53U, 0xdebb9ec5U, 0x47b2cf7fU, 0x30b5ffe9U,
+ 0xbdbdf21cU, 0xcabac28aU, 0x53b39330U, 0x24b4a3a6U, 0xbad03605U,
+ 0xcdd70693U, 0x54de5729U, 0x23d967bfU, 0xb3667a2eU, 0xc4614ab8U,
+ 0x5d681b02U, 0x2a6f2b94U, 0xb40bbe37U, 0xc30c8ea1U, 0x5a05df1bU,
+ 0x2d02ef8dU
+};
+
+static u32 partial_crc32_one(u8 c, u32 crc)
+{
+ return crctab32[(crc ^ c) & 0xff] ^ (crc >> 8);
+}
+
+static u32 partial_crc32(const u8 *s, int len, u32 crc)
+{
+ while (len--)
+ crc = partial_crc32_one(*s++, crc);
+ return crc;
+}
+
static void die(const char * str, ...)
{
va_list args;
@@ -74,6 +143,7 @@ int main(int argc, char ** argv)
FILE *file;
int fd;
void *kernel;
+ u32 crc = 0xffffffffUL;
if (argc > 2 && !strcmp(argv[1], "-b"))
{
@@ -144,7 +214,8 @@ int main(int argc, char ** argv)
kernel = mmap(NULL, sz, PROT_READ, MAP_SHARED, fd, 0);
if (kernel == MAP_FAILED)
die("Unable to mmap '%s': %m", argv[2]);
- sys_size = (sz + 15) / 16;
+ /* Number of 16-byte paragraphs, including space for a 4-byte CRC */
+ sys_size = (sz + 15 + 4) / 16;
if (!is_big_kernel && sys_size > DEF_SYSSIZE)
die("System is too big. Try using bzImage or modules.");
@@ -155,12 +226,27 @@ int main(int argc, char ** argv)
buf[0x1f6] = sys_size >> 16;
buf[0x1f7] = sys_size >> 24;
+ crc = partial_crc32(buf, i, crc);
if (fwrite(buf, 1, i, stdout) != i)
die("Writing setup failed");
/* Copy the kernel code */
+ crc = partial_crc32(kernel, sz, crc);
if (fwrite(kernel, 1, sz, stdout) != sz)
die("Writing kernel failed");
+
+ /* Add padding leaving 4 bytes for the checksum */
+ while (sz++ < (sys_size*16) - 4) {
+ crc = partial_crc32_one('\0', crc);
+ if (fwrite("\0", 1, 1, stdout) != 1)
+ die("Writing padding failed");
+ }
+
+ /* Write the CRC */
+ fprintf(stderr, "CRC %lx\n", crc);
+ if (fwrite(&crc, 1, 4, stdout) != 4)
+ die("Writing CRC failed");
+
close(fd);
/* Everything is OK */
--
1.5.3.8
--
Ian Campbell
In matters of principle, stand like a rock;
in matters of taste, swim with the current.
-- Thomas Jefferson
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