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fix(kernel): a GPT disk with a bad header, or an unreadable first block, is not used

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The increment 2 final review's minors 1-4 (Captain Bob, 2026-10-27: "fix 1-4"):
1. A protective MBR with no "EFI PART" header is GPT_BAD, not GPT_NONE: the
   MBR says it is a GPT disk, and a GPT disk is never attached whole.
2. A disk whose block 0 cannot be read is GPT_EIO: "GPT: a USB drive could
   not be read -- not used", nothing attached (it was read raw, attached
   whole, and a raw Zuse drive behind it logged her in).
3. The entry array's LBA is checked against the disk's size directly.
4. gpt_bad_entries: the entry array changed, the header valid -- refused.
Harness modes gpt_no_header, gpt_read_error (blkdebug EIO on sector 0),
gpt_bad_entries. The plan carries the amendment.

Red (amd64): gpt_no_header 070335, gpt_read_error 070717 FAIL;
gpt_bad_entries 070048 PASS (existing check, now pinned). Green: every GPT
mode on amd64 071113-072933; gpt_zuse, gpt_read_error, gpt_no_header on
aarch64 073222-074047 and riscv64 074526-075535; the identity gate's and
increment 1's sessions 080036-082345, emergency 083130 (082635 was run
without EMERGENCY_CONSOLE_ENABLED=1 -- a harness invocation error).
Accepted: suite EXIT 0; 093121, 093352, 093750, POST 538/538, dict_hash
0xfec8c47cfc6f437f; test-32, 0 failures.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
rajames
2026-10-27 12:17:00 -04:00
co-authored by Claude Opus 5.5
parent f612bb37a9
commit 2e71f7aa0d
65 changed files with 4910 additions and 18 deletions
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kernel/include/starkernel/gpt.h
+3 -2
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@@ -19,8 +19,9 @@ typedef struct {
} gpt_part_t;
#define GPT_OK 0 /* a valid GPT */
#define GPT_NONE 1 /* not a GPT disk (or one whose sectors are not 512 bytes): read it raw */
#define GPT_BAD 2 /* a GPT, but its header or entry array does not check out: not used */
#define GPT_NONE 1 /* not a GPT disk -- no protective MBR -- (or one whose sectors are not 512 bytes): read it raw */
#define GPT_BAD 2 /* a protective MBR, but its header or entry array does not check out: not used */
#define GPT_EIO 3 /* its first block could not be read: not used */
/* Read `disk`'s protective MBR, primary GPT header and partition-entry array,
* checking both CRC-32s, the revision, the sizes and the geometry. On GPT_OK,