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Corrected understanding of relation of RFC 4122 and UEFI GUID.

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Thanks Andrei Borzenkov.
This commit is contained in:
Thomas Schmitt 2016-08-14 22:24:53 +02:00
parent 866f647fad
commit 9d64318502
2 changed files with 16 additions and 14 deletions
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23
libisofs/libisofs.h
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@ -2597,26 +2597,29 @@ int iso_write_opts_set_efi_bootp(IsoWriteOpts *opts, char *image_path,
/**
* Control whether the emerging GPT gets a pseudo-randomly generated disk GUID
* or * whether it gets a user supplied GUID.
* The partition GUIDs will be generated in a reproducible way by exoring a
* little-endian 32 bit counter with the disk GUID beginning at byte offset 9.
* or whether it gets a user supplied GUID.
* The partition GUIDs will be generated in a reproducible way by exoring the
* little-endian 32 bit partion number with the disk GUID beginning at byte
* offset 9.
*
* @param opts
* The option set to be manipulated.
* @param guid
* 16 bytes of user supplied GUID.
* The upper 4 bit of guid[6] and guid[7] should bear the value 4 to
* express the version 4 in both endiannesses. Bit 7 of byte[8] should
* be set to 1 and bit 6 be set to 0, in order to express the RFC 4122
* variant of GUID, where version 4 means "random".
* 16 bytes of user supplied GUID. Readily byte-swapped as prescribed by
* UEFI specs: 4 byte, 2 byte, 2 byte as little-endian. The rest as
* big-endian.
* The upper 4 bit of guid[7] should bear the value 4 to express the
* RFC 4122 version 4. Bit 7 of byte[8] should be set to 1 and bit 6
* be set to 0, in order to express the RFC 4122 variant of UUID,
* where version 4 means "pseudo-random uuid".
* @param mode
* 0 = ignore parameter guid and produce the GPT disk GUID by a
* pseudo-random algorithm. This is the default setting.
* 1 = use parameter guid as GPT disk GUID
* 2 = ignore parameter guid and derive the GPT disk GUID from
* parameter vol_uuid of iso_write_opts_set_pvd_times().
* The 16 bytes of vol_uuid get copied and bytes 6, 7, 8 get their
* upper bits changed to comply to RFC 4122.
* The 16 bytes of vol_uuid get copied and bytes 7, 8 get their
* upper bits changed to comply to RFC 4122 and UEFI.
* Error ISO_GPT_NO_VOL_UUID will occur if image production begins
* before vol_uuid was set.
*

7
libisofs/system_area.c
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@ -2362,10 +2362,9 @@ uint32_t iso_crc32_gpt(unsigned char *data, int count, int flag)
void iso_mark_guid_version_4(uint8_t *u)
{
/* Mark as UUID version 4. RFC 4122 says u[6], but isohybrid swapping
effectively puts the 4 into u[7]. So i mark both. 4 bits wasted.
/* Mark as UUID version 4. RFC 4122 says u[6], but UEFI prescribes
bytes 6 and 7 to be swapped.
*/
u[6] = (u[6] & 0x0f) | 0x40;
u[7] = (u[7] & 0x0f) | 0x40;
/* Variant is "1 0 x" as described in RFC 4122.
@ -2389,7 +2388,7 @@ void iso_generate_gpt_guid(uint8_t guid[16])
#else
uint8_t *u;
/* produced by uuid_generate() and byte-swapped to isohybrid.c habits */
/* produced by uuid_generate() and byte-swapped to UEFI specs */
static uint8_t uuid_template[16] = {
0xee, 0x29, 0x9d, 0xfc, 0x65, 0xcc, 0x7c, 0x40,
0x92, 0x61, 0x5b, 0xcd, 0x6f, 0xed, 0x08, 0x34