|Summary:||Several errors in pmbr: 64-bits arithmetics and some others|
|Product:||Base System||Reporter:||Emrion <kmachine>|
|Component:||misc||Assignee:||Warner Losh <imp>|
|Severity:||Affects Some People||CC:||emaste, imp, kmachine|
Description Emrion 2018-11-12 19:45:13 UTC
These issues have low impact because they require precise circumstances to trigger one of them. The disk must be > 2 TiB in size and either: - The primary GPT header is dammaged. - The freebsd-boot partiton is located farther than the first 2 TiB of the disc and one of its sectors takes place at a lba value that makes the higher 32 bits of this very value change. Errors and corrections folow: * Lines 117 - 118 main.3a: decl (%si) # 0x0(%si) = last sec (0-31) movw $2,%cx Should be: main.3a: subl $1, (%si) # 0x0(%si) = last sec (0-31) sbbl $0, 4(%si) movw $4,%cx -> Copies only two 16-bits words but it's a 64-bits value. Moreover, decrements this 64-bit value without care for a possible carry. * Line 131 movb $0x10,%cl repe cmpsb Should be: movw $0x10,%cx repe cmpsb -> It's CX the counter for repe not CL. It works as is but it's dangerous to keep that. * Lines 153 - 154 next_boot: incl (%si) # Next LBA adcl $0,4(%si) Should be: next_boot: addl $1, (%si) # Next LBA adcl $0,4(%si) -> inc instruction doesn't affect the carry flag. * Lines 174 - 175 incl GPT_ADDR+GPT_PART_LBA # Next sector adcl $0,GPT_ADDR+GPT_PART_LBA+4 Should be: addl $1, GPT_ADDR+GPT_PART_LBA. adcl $0,GPT_ADDR+GPT_PART_LBA+4 -> Same as before.
Comment 1 Emrion 2019-01-10 18:49:46 UTC
Created attachment 200996 [details] pmbr source code patched
Comment 2 Emrion 2019-01-10 18:52:13 UTC
For your information, I compiled the code corrected as indicated above and installed it on a 12.0-RELEASE. It works. However, I can't test the cases where the original pmbr would crash as I don't have a disk > 2 TiB.