
Strumenti per il debug del kernel Linux su Bochs (inclusi simboli, debugger nativo Bochs e IDA PRO)
Strumenti per il debug del kernel Linux su Bochs (inclusi simboli, debugger Bochs nativo e IDA PRO)


Segui i passaggi seguenti:
usa semplicemente il comando nm sull'immagine del kernel di debug, esempio per Debian:
1- Installa l'immagine dbg
root@debian# apt-get install linux-image-$(uname -r)-dbg
2- Verifica che nm funzioni sull'immagine dbg:
dreg@debian# nm /usr/lib/debug/boot/vmlinux-$(uname -r) | tail
ffffffff8207d7c0 d zswap_same_filled_pages_enabled
ffffffff8262b54c b zswap_stored_pages
ffffffff8262b420 b zswap_trees
ffffffff81225df0 t zswap_update_total_size
ffffffff81226a50 t zswap_writeback_entry
ffffffff8262b538 b zswap_written_back_pages
ffffffff81c41fb8 r zswap_zpool_ops
ffffffff8207d7e0 d zswap_zpool_param_ops
3- Genera un file di output valido per linsymtobch.py:
dreg@debian# nm /usr/lib/debug/boot/vmlinux-$(uname -r) > nm_output.txt
Puoi anche usare/combinare altri tipi di strumenti, guarda questo repository per ulteriori suggerimenti:
https://github.com/therealdreg/linux_kernel_debug_disassemble_ida_vmware
Usa linsymtobch.py per convertire un file di output in stile nm in un file syms di Bochs:
python linsymbtobch.py symbol_file.txt output_bochs_syms.txt [letter 1] [letter 2] [letter 3] .... [--verbose]
Esempio:
./linsymtobch.py nm_output.txt output_bochs_syms.txt
Output:
https://github.com/therealdreg/bochs_linux_kernel_debugging
-
MIT LICENSE Copyright <2020>
David Reguera Garcia aka Dreg - [email protected]
http://www.fr33project.org/ - https://github.com/therealdreg
usage: python linsymbtobch.py symbol_file.txt output_bochs_syms.txt [letter 1] [letter 2] [letter 3] .... [--verbose]
where letters can be empty for all symbols or a combination:
If lowercase, the symbol is local; if uppercase, the symbol is global (external).
------------------------------------
"A" The symbol's value is absolute, and will not be changed by further linking.
"B" "b" The symbol is in the uninitialized data section (known as BSS ).
"C" The symbol is common. Common symbols are uninitialized data. When linking, multiple common symbols may appear with the same name. If the symbol is defined anywhere, the common symbols are treated as undefined references.
"D" "d" The symbol is in the initialized data section.
"G" "g" The symbol is in an initialized data section for small objects. Some object file formats permit more efficient access to small data objects, such as a global int variable as opposed to a large global array.
"i" For PE format files this indicates that the symbol is in a section specific to the implementation of DLLs. For ELF format files this indicates that the symbol is an indirect function. This is a GNU extension to the standard set of ELF symbol types. It indicates a symbol which if referenced by a relocation does not evaluate to its address, but instead must be invoked at runtime. The runtime execution will then return the value to be used in the relocation.
"N" The symbol is a debugging symbol.
"p" The symbols is in a stack unwind section.
"R" "r" The symbol is in a read only data section.
"S" "s" The symbol is in an uninitialized data section for small objects.
"T" "t" The symbol is in the text (code) section.
"U" The symbol is undefined.
"u" The symbol is a unique global symbol. This is a GNU extension to the standard set of ELF symbol bindings. For such a symbol the dynamic linker will make sure that in the entire process there is just one symbol with this name and type in use.
"V" "v" The symbol is a weak object. When a weak defined symbol is linked with a normal defined symbol, the normal defined symbol is used with no error. When a weak undefined symbol is linked and the symbol is not defined, the value of the weak symbol becomes zero with no error. On some systems, uppercase indicates that a default value has been specified.
"W" "w" The symbol is a weak symbol that has not been specifically tagged as a weak object symbol. When a weak defined symbol is linked with a normal defined symbol, the normal defined symbol is used with no error. When a weak undefined symbol is linked and the symbol is not defined, the value of the symbol is determined in a system-specific manner without error. On some systems, uppercase indicates that a default value has been specified.
"-" The symbol is a stabs symbol in an a.out object file. In this case, the next values printed are the stabs other field, the stabs desc field, and the stab type. Stabs symbols are used to hold debugging information.
"?" The symbol type is unknown, or object file format specific.
------------------------------------
0xffffffff81412a30 T_aa_af_perm
0xffffffff813ff4f0 T_aa_alloc_profile
0xffffffff8140c420 T_aa_alloc_proxy
0xffffffff82c71f0d T_aa_alloc_root_ns
0xffffffff81409e20 T_aa_alloc_secid
0xffffffff813f7bc0 T_aa_apply_modes_to_perms
0xffffffff813f6030 T_aa_audit
0xffffffff8140a210 T_aa_audit_file
0xffffffff813f6010 T_aa_audit_msg
...
done!
total symbols written: 115131
total letters written: A B D R T V W a b d r t
total letters found: A B D R T V W a b d r t
Esempio di filtraggio di alcuni simboli:
./linsymtobch.py nm_output.txt output_bochs_syms.txt T V d
Carica il file generato nel debugger di Bochs con "ldsym global", esempio:
ldsym global "C:\Users\leno\Desktop\bochs_linux_kernel_debugging\output_bochs_syms.txt"
Fatto! Prova se i simboli funzionano eseguendo alcuni comandi nel debugger di Bochs:

Modifica "C:\Program Files\IDA Pro 7.7\cfg\dbg_bochs.cfg"
BOCHSDBG = "C:\\Users\\leno\\Desktop\\Bochs-pruebas\\bochs\\bochs.exe";
BOCHSRC = "C:\\Users\\leno\\Desktop\\Bochs-pruebas\\bochs\\.bochsrc";
Vai su IDA .....
Debugger -> Esegui -> Debugger Bochs locale
Applicazione:
C:\Users\leno\Desktop\Bochs-pruebas\bochs\.bochsrc
Fai clic su Opzioni di debug -> Imposta opzioni specifiche -> Seleziona immagine disco
Scarica ida_load_names.py da questo repository:
https://github.com/therealdreg/symseghelper
Apri IDA PRO, avvia una sessione di debug Bochs e vai su File -> File script
Seleziona ida_load_names.py; questo script ti chiederà il file dei simboli Bochs generato.
Fatto!
Dopodiché puoi anche caricare i simboli nel debugger Bochs nativo (è in esecuzione all'interno di IDA PRO). Basta selezionare Bochs nella riga di comando di IDA ed eseguire "ldsym global"
IDA PRO con i simboli Bochs (ida_load_names.py) + debugger nativo Bochs con i simboli (ldsym global), il meglio dei due mondi:

ATTENZIONE: la tua strumentazione Bochs personalizzata può causare problemi nel debugger Bochs locale di IDA PRO
Script helper per il debug di Windows con simboli per Bochs e IDA Pro (file PDB). Molto comodi per la modalità utente <--> modalità kernel:
Script helper per il debug del kernel Linux con IDA Pro su VMware + stub GDB (inclusi alcuni helper per i simboli):
Estrae i simboli PDB, incluso il supporto per il formato di debug di Bochs (con supporto Wine):
Script helper per il debug del kernel Windows con IDA Pro nel debugger Bochs nativo: