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authorNavan Chauhan <navanchauhan@gmail.com>2023-10-04 16:59:12 -0600
committerNavan Chauhan <navanchauhan@gmail.com>2023-10-04 16:59:12 -0600
commit6b57097c8fd34e86658a7b8e8ac3080c23c462b4 (patch)
tree4806ab78ec34fd5fc67c93b52c85deb19af50a4c /Content
parentf746534e2e15e173f0100dbc6dbd9e428157f0fe (diff)
adding phase 6
Diffstat (limited to 'Content')
-rw-r--r--Content/posts/2023-10-04-bomb-lab.md218
1 files changed, 217 insertions, 1 deletions
diff --git a/Content/posts/2023-10-04-bomb-lab.md b/Content/posts/2023-10-04-bomb-lab.md
index 98c5272..d72322f 100644
--- a/Content/posts/2023-10-04-bomb-lab.md
+++ b/Content/posts/2023-10-04-bomb-lab.md
@@ -611,7 +611,7 @@ jmp 0x5555555557b4 <func4+27>
We can either try to compute the values by hand, or write a simple script in Python to get the answer.
-```
+```python
def func4(edi, esi=0, edx=20):
ecx = (edx - esi) // 2 + esi
if ecx > edi:
@@ -778,3 +778,219 @@ Awesome!
## Phase 6
+```
+Good work! On to the next...
+test string
+
+Breakpoint 1, 0x0000555555555899 in phase_6 ()
+(gdb) disas phase_6
+Dump of assembler code for function phase_6:
+=> 0x0000555555555899 <+0>: endbr64
+ 0x000055555555589d <+4>: push %r15
+ 0x000055555555589f <+6>: push %r14
+ 0x00005555555558a1 <+8>: push %r13
+ 0x00005555555558a3 <+10>: push %r12
+ 0x00005555555558a5 <+12>: push %rbp
+ 0x00005555555558a6 <+13>: push %rbx
+ 0x00005555555558a7 <+14>: sub $0x68,%rsp
+ 0x00005555555558ab <+18>: lea 0x40(%rsp),%rax
+ 0x00005555555558b0 <+23>: mov %rax,%r14
+ 0x00005555555558b3 <+26>: mov %rax,0x8(%rsp)
+ 0x00005555555558b8 <+31>: mov %rax,%rsi
+ 0x00005555555558bb <+34>: call 0x555555555d97 <read_six_numbers>
+ 0x00005555555558c0 <+39>: mov %r14,%r12
+ 0x00005555555558c3 <+42>: mov $0x1,%r15d
+ 0x00005555555558c9 <+48>: mov %r14,%r13
+ 0x00005555555558cc <+51>: jmp 0x555555555997 <phase_6+254>
+ 0x00005555555558d1 <+56>: call 0x555555555d4a <explode_bomb>
+ 0x00005555555558d6 <+61>: jmp 0x5555555559a9 <phase_6+272>
+ 0x00005555555558db <+66>: add $0x1,%rbx
+ 0x00005555555558df <+70>: cmp $0x5,%ebx
+ 0x00005555555558e2 <+73>: jg 0x55555555598f <phase_6+246>
+ 0x00005555555558e8 <+79>: mov 0x0(%r13,%rbx,4),%eax
+ 0x00005555555558ed <+84>: cmp %eax,0x0(%rbp)
+ 0x00005555555558f0 <+87>: jne 0x5555555558db <phase_6+66>
+ 0x00005555555558f2 <+89>: call 0x555555555d4a <explode_bomb>
+ 0x00005555555558f7 <+94>: jmp 0x5555555558db <phase_6+66>
+ 0x00005555555558f9 <+96>: mov 0x8(%rsp),%rdx
+ 0x00005555555558fe <+101>: add $0x18,%rdx
+ 0x0000555555555902 <+105>: mov $0x7,%ecx
+ 0x0000555555555907 <+110>: mov %ecx,%eax
+ 0x0000555555555909 <+112>: sub (%r12),%eax
+ 0x000055555555590d <+116>: mov %eax,(%r12)
+ 0x0000555555555911 <+120>: add $0x4,%r12
+ 0x0000555555555915 <+124>: cmp %r12,%rdx
+ 0x0000555555555918 <+127>: jne 0x555555555907 <phase_6+110>
+ 0x000055555555591a <+129>: mov $0x0,%esi
+ 0x000055555555591f <+134>: mov 0x40(%rsp,%rsi,4),%ecx
+ 0x0000555555555923 <+138>: mov $0x1,%eax
+ 0x0000555555555928 <+143>: lea 0x3d01(%rip),%rdx # 0x555555559630 <node1>
+--Type <RET> for more, q to quit, c to continue without paging--
+ 0x000055555555592f <+150>: cmp $0x1,%ecx
+ 0x0000555555555932 <+153>: jle 0x55555555593f <phase_6+166>
+ 0x0000555555555934 <+155>: mov 0x8(%rdx),%rdx
+ 0x0000555555555938 <+159>: add $0x1,%eax
+ 0x000055555555593b <+162>: cmp %ecx,%eax
+ 0x000055555555593d <+164>: jne 0x555555555934 <phase_6+155>
+ 0x000055555555593f <+166>: mov %rdx,0x10(%rsp,%rsi,8)
+ 0x0000555555555944 <+171>: add $0x1,%rsi
+ 0x0000555555555948 <+175>: cmp $0x6,%rsi
+ 0x000055555555594c <+179>: jne 0x55555555591f <phase_6+134>
+ 0x000055555555594e <+181>: mov 0x10(%rsp),%rbx
+ 0x0000555555555953 <+186>: mov 0x18(%rsp),%rax
+ 0x0000555555555958 <+191>: mov %rax,0x8(%rbx)
+ 0x000055555555595c <+195>: mov 0x20(%rsp),%rdx
+ 0x0000555555555961 <+200>: mov %rdx,0x8(%rax)
+ 0x0000555555555965 <+204>: mov 0x28(%rsp),%rax
+ 0x000055555555596a <+209>: mov %rax,0x8(%rdx)
+ 0x000055555555596e <+213>: mov 0x30(%rsp),%rdx
+ 0x0000555555555973 <+218>: mov %rdx,0x8(%rax)
+ 0x0000555555555977 <+222>: mov 0x38(%rsp),%rax
+ 0x000055555555597c <+227>: mov %rax,0x8(%rdx)
+ 0x0000555555555980 <+231>: movq $0x0,0x8(%rax)
+ 0x0000555555555988 <+239>: mov $0x5,%ebp
+ 0x000055555555598d <+244>: jmp 0x5555555559c4 <phase_6+299>
+ 0x000055555555598f <+246>: add $0x1,%r15
+ 0x0000555555555993 <+250>: add $0x4,%r14
+ 0x0000555555555997 <+254>: mov %r14,%rbp
+ 0x000055555555599a <+257>: mov (%r14),%eax
+ 0x000055555555599d <+260>: sub $0x1,%eax
+ 0x00005555555559a0 <+263>: cmp $0x5,%eax
+ 0x00005555555559a3 <+266>: ja 0x5555555558d1 <phase_6+56>
+ 0x00005555555559a9 <+272>: cmp $0x5,%r15d
+ 0x00005555555559ad <+276>: jg 0x5555555558f9 <phase_6+96>
+ 0x00005555555559b3 <+282>: mov %r15,%rbx
+ 0x00005555555559b6 <+285>: jmp 0x5555555558e8 <phase_6+79>
+ 0x00005555555559bb <+290>: mov 0x8(%rbx),%rbx
+ 0x00005555555559bf <+294>: sub $0x1,%ebp
+ 0x00005555555559c2 <+297>: je 0x5555555559d5 <phase_6+316>
+ 0x00005555555559c4 <+299>: mov 0x8(%rbx),%rax
+ 0x00005555555559c8 <+303>: mov (%rax),%eax
+ 0x00005555555559ca <+305>: cmp %eax,(%rbx)
+--Type <RET> for more, q to quit, c to continue without paging--
+ 0x00005555555559cc <+307>: jge 0x5555555559bb <phase_6+290>
+ 0x00005555555559ce <+309>: call 0x555555555d4a <explode_bomb>
+ 0x00005555555559d3 <+314>: jmp 0x5555555559bb <phase_6+290>
+ 0x00005555555559d5 <+316>: add $0x68,%rsp
+ 0x00005555555559d9 <+320>: pop %rbx
+ 0x00005555555559da <+321>: pop %rbp
+ 0x00005555555559db <+322>: pop %r12
+ 0x00005555555559dd <+324>: pop %r13
+ 0x00005555555559df <+326>: pop %r14
+ 0x00005555555559e1 <+328>: pop %r15
+ 0x00005555555559e3 <+330>: ret
+End of assembler dump.
+(gdb)
+```
+
+Again, we see the familiar `read_six_digits` function.
+
+Let us analyse this function in chunks:
+
+```
+ 0x00005555555558bb <+34>: call 0x555555555d97 <read_six_numbers>
+ 0x00005555555558c0 <+39>: mov %r14,%r12
+ 0x00005555555558c3 <+42>: mov $0x1,%r15d
+ 0x00005555555558c9 <+48>: mov %r14,%r13
+ 0x00005555555558cc <+51>: jmp 0x555555555997 <phase_6+254>
+```
+
+1. Read six numbers
+2. Initialise Registers:
+ 2.1. `mov %r14,%r12`: `%r14` should be pointing to the location of the stack where the numbers were read into. This address is copied onto `%r12`
+ 2.2. `mov $0x1,%r15d`: The value `1` is moved into `%r15` register (probably acting like a counter)
+ 2.3. `mov %r14,%r13`: The value is also copied to `%r13`
+3. Jump to start of loop:
+
+```
+ 0x0000555555555997 <+254>: mov %r14,%rbp
+ 0x000055555555599a <+257>: mov (%r14),%eax
+ 0x000055555555599d <+260>: sub $0x1,%eax
+ 0x00005555555559a0 <+263>: cmp $0x5,%eax
+ 0x00005555555559a3 <+266>: ja 0x5555555558d1 <phase_6+56>
+```
+
+1. Initialise register and point to first number in sequence
+2. Adjust number(s):
+ 2.1. `mov (%r14),%eax` -> load the current number in the sequence
+ 2.2. `sub $0x1,%eax` -> decrement number by 1
+3. Validation
+ 3.1. `cmp $0x5,%eax`: This compares the adjusted value in `%eax` with 5.
+ 3.2. `ja 0x5555555558d1 <phase_6+56>`: jump if given value is > 5 or < 0
+
+=> All numbers should be between 1 and 6.
+
+```
+ 0x00005555555559a9 <+272>: cmp $0x5,%r15d
+ 0x00005555555559ad <+276>: jg 0x5555555558f9 <phase_6+96>
+```
+
+This checks if the value stored in `%r15` is > 5, if it is then it jumps somewhere else. This validates our assumption that `%r15` is acting as a counter.
+
+```
+ 0x00005555555559b3 <+282>: mov %r15,%rbx
+ 0x00005555555559b6 <+285>: jmp 0x5555555558e8 <phase_6+79>
+```
+
+Let us jump to +79
+
+```
+ 0x00005555555558e8 <+79>: mov 0x0(%r13,%rbx,4),%eax
+ 0x00005555555558ed <+84>: cmp %eax,0x0(%rbp)
+ 0x00005555555558f0 <+87>: jne 0x5555555558db <phase_6+66>
+ 0x00005555555558f2 <+89>: call 0x555555555d4a <explode_bomb>
+ 0x00005555555558f7 <+94>: jmp 0x5555555558db <phase_6+66>
+```
+
+This section deals with checking if all the numbers in the sequence are unique or not. Thus, we need to ensure out 6 digits are unique
+
+```
+ 0x00005555555558db <+66>: add $0x1,%rbx // Increments by 1
+ 0x00005555555558df <+70>: cmp $0x5,%ebx
+ 0x00005555555558e2 <+73>: jg 0x55555555598f <phase_6+246> // Jump if > 5 (Loop iterations are complete)
+ 0x00005555555558e8 <+79>: mov 0x0(%r13,%rbx,4),%eax
+ 0x00005555555558ed <+84>: cmp %eax,0x0(%rbp)
+ 0x00005555555558f0 <+87>: jne 0x5555555558db <phase_6+66> // Again, check if the number being seen is unique
+```
+
+Now we know that the numbers are unique, between 1-6 (inclusive).
+
+After stepping through the instructions, we can also see that the numbers are being transformed:
+* By subtracting it from 7 (mov $0x7,%ecx followed by sub (%r12),%eax)
+* This effectively maps the numbers as follows: 1 to 6, 2 to 5, 3 to 4, 4 to 3, 5 to 2, and 6 to 1.
+
+Let us try to figure out what ` 0x0000555555555928 <+143>: lea 0x3d01(%rip),%rdx # 0x555555559630 <node1>` is:
+
+```
+(gdb) x/30wx 0x555555559630
+0x555555559630 <node1>: 0x000000d9 0x00000001 0x55559640 0x00005555
+0x555555559640 <node2>: 0x000003ab 0x00000002 0x55559650 0x00005555
+0x555555559650 <node3>: 0x0000014f 0x00000003 0x55559660 0x00005555
+0x555555559660 <node4>: 0x000000a1 0x00000004 0x55559670 0x00005555
+0x555555559670 <node5>: 0x000001b3 0x00000005 0x55559120 0x00005555
+0x555555559680 <host_table>: 0x555573f5 0x00005555 0x5555740f 0x00005555
+0x555555559690 <host_table+16>: 0x55557429 0x00005555 0x00000000 0x00000000
+0x5555555596a0 <host_table+32>: 0x00000000 0x00000000
+(gdb) x/30wx 0x555555559120
+0x555555559120 <node6>: 0x000002da 0x00000006 0x00000000 0x00000000
+0x555555559130: 0x00000000 0x00000000 0x00000000 0x00000000
+0x555555559140 <userid>: 0x61767861 0x38383535 0x00000000 0x00000000
+0x555555559150 <userid+16>: 0x00000000 0x00000000 0x00000000 0x00000000
+0x555555559160 <userid+32>: 0x00000000 0x00000000 0x00000000 0x00000000
+0x555555559170 <userid+48>: 0x00000000 0x00000000 0x00000000 0x00000000
+0x555555559180 <userid+64>: 0x00000000 0x00000000 0x00000000 0x00000000
+0x555555559190 <userid+80>: 0x00000000 0x00000000
+(gdb)
+```
+
+It appears that this is a linked list. With roughly the following structure:
+
+```cpp
+struct node {
+ int value;
+ int index;
+ struct node *next;
+};
+```
+
+Let us convert the values into decimal