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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
Download Patch File Download Diff File Expand all files Collapse all files
scripts/qemu_session.py
+37 -10
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@@ -39,6 +39,10 @@ the stick's, plan 2026-10-26-stick-1-screen-and-keyboard.md):
gpt_hotplug ... pulled: session ended; added again: prompt
gpt_foreign a GPT drive with only a Linux partition: no identity, not attached (info level)
gpt_bad_crc the gpt_zuse image with its header CRC broken: not used, said so, not attached
gpt_bad_entries ... its entry array changed (the header intact): the same
gpt_no_header ... its "EFI PART" signature gone, the protective MBR kept: the same
gpt_read_error the raw Zuse drive with reads of its sector 0 failing (blkdebug): not used,
said so, not attached
virtio_kbd aarch64/riscv64: QEMU's virtio keyboard types 7 ok
Needs only Python 3. One QEMU at a time (.claude/CLAUDE.md).
@@ -57,7 +61,8 @@ ap.add_argument("--make", default="")
ap.add_argument("--no-zuse", action="store_true")
a = ap.parse_args()
NO_ZUSE_MODES = {"gpt_zuse", "gpt_hotplug", "gpt_foreign", "gpt_bad_crc", "headless", "hotplug", "midpull", "waitpull", "typeahead", "emergency",
NO_ZUSE_MODES = {"gpt_zuse", "gpt_hotplug", "gpt_foreign", "gpt_bad_crc", "gpt_bad_entries", "gpt_no_header",
"gpt_read_error", "headless", "hotplug", "midpull", "waitpull", "typeahead", "emergency",
"alttab_after_logout", "alttab_before_pull", "emergency_pull",
"screen_dark_until_login", "screen_console_after_login", "screen_dark_after_logout",
"kbd_typeahead"}
@@ -191,9 +196,11 @@ GPT_IDENTITY = "23BEBFE1-4817-4CF3-A537-9069BF159788"
GPT_LINUX = "0FC63DAF-8483-4772-8E79-3D69D8477DE4"
def make_gpt_image(path, ptype, payload, mib=72, break_crc=False):
def make_gpt_image(path, ptype, payload, mib=72, break_crc=False, break_entries=False, break_sig=False):
"""A GPT disk image: one partition at LBA 2048, 131072 sectors (64 MiB), of type
`ptype`, holding `payload` from its start; optionally the primary header's CRC broken."""
`ptype`, holding `payload` from its start; optionally the primary header's CRC broken,
a byte of the entry array changed (the header left valid), or the header's "EFI PART"
signature zeroed (the protective MBR left in place)."""
subprocess.run(["truncate", "-s", f"{mib}M", path], check=True)
sf = shutil.which("sfdisk") or "/usr/sbin/sfdisk"
subprocess.run([sf, "--quiet", path], input=f"label: gpt\nstart=2048, size=131072, type={ptype}\n",
@@ -206,6 +213,16 @@ def make_gpt_image(path, ptype, payload, mib=72, break_crc=False):
b = f.read(1)
f.seek(512 + 16)
f.write(bytes([b[0] ^ 0xFF]))
if break_entries:
with open(path, "r+b") as f:
f.seek(1024 + 56) # entry 0's name, inside the CRC'd entry array
b = f.read(1)
f.seek(1024 + 56)
f.write(bytes([b[0] ^ 0xFF]))
if break_sig:
with open(path, "r+b") as f:
f.seek(512) # the primary header's Signature
f.write(bytes(8))
def blk_lines():
@@ -239,9 +256,12 @@ def screen():
return w, h, lit, px
def add_zuse(n, img=None):
qcmd("blockdev-add", driver="raw", **{"node-name": f"zuse{n}"},
file={"driver": "file", "filename": img or zimg})
def add_zuse(n, img=None, fail_sector0=False):
f = {"driver": "file", "filename": img or zimg}
if fail_sector0: # every read touching sector 0 fails, EIO
f = {"driver": "blkdebug", "image": f,
"inject-error": [{"event": "none", "iotype": "read", "sector": 0, "errno": 5}]}
qcmd("blockdev-add", driver="raw", **{"node-name": f"zuse{n}"}, file=f)
qcmd("device_add", driver="usb-storage", bus="xhci0.0", port="1",
drive=f"zuse{n}", id=f"zusedev{n}")
@@ -437,13 +457,18 @@ elif m == "emergency_pull":
_, _, _, px2 = screen()
check("the screen changed with what was typed", px2 != px1)
elif m in ("gpt_zuse", "gpt_hotplug", "gpt_foreign", "gpt_bad_crc"):
elif m in ("gpt_zuse", "gpt_hotplug", "gpt_foreign", "gpt_bad_crc", "gpt_bad_entries", "gpt_no_header",
"gpt_read_error"):
gimg = os.path.join(work, "gpt.img")
make_gpt_image(gimg, GPT_LINUX if m == "gpt_foreign" else GPT_IDENTITY, zimg,
break_crc=(m == "gpt_bad_crc"))
break_crc=(m == "gpt_bad_crc"), break_entries=(m == "gpt_bad_entries"),
break_sig=(m == "gpt_no_header"))
check("no ok> for 10 s with no drive", not wait_for(ANYPROMPT, 10))
b0 = blk_lines()
add_zuse(1, gimg)
if m == "gpt_read_error":
add_zuse(1, zimg, fail_sector0=True) # the raw Zuse drive: no GPT, but block 0 unreadable
else:
add_zuse(1, gimg)
if m in ("gpt_zuse", "gpt_hotplug"):
check("Zuse: identity confirmed", wait_for(r"Zuse: identity confirmed from attached thumbdrive", 120))
check("[zuse@Hera] ok>", wait_for(PROMPT, 60))
@@ -463,8 +488,10 @@ elif m in ("gpt_zuse", "gpt_hotplug", "gpt_foreign", "gpt_bad_crc"):
add_zuse(2, gimg)
check("[zuse@Hera] ok> again", wait_for(PROMPT, 120, p))
else:
if m == "gpt_bad_crc":
if m in ("gpt_bad_crc", "gpt_bad_entries", "gpt_no_header"):
check("the damaged table is said so", wait_for(r"GPT: a USB drive has a damaged partition table -- not used", 60))
if m == "gpt_read_error":
check("the unreadable drive is said so", wait_for(r"GPT: a USB drive could not be read -- not used", 60))
check("no ok> for 30 s", not wait_for(ANYPROMPT, 30))
check("no identity", count(r"Zuse: identity confirmed") == 0)
check(f"not attached (blk: lines {b0} -> {blk_lines()})", blk_lines() == b0)