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diff --git a/docs/feed.rss b/docs/feed.rss index 1631f83..8b5469b 100644 --- a/docs/feed.rss +++ b/docs/feed.rss @@ -4,8 +4,8 @@ <title>Navan's Archive</title> <description>Rare Tips, Tricks and Posts</description> <link>https://web.navan.dev/</link><language>en</language> - <lastBuildDate>Thu, 15 Jun 2023 19:33:51 -0000</lastBuildDate> - <pubDate>Thu, 15 Jun 2023 19:33:51 -0000</pubDate> + <lastBuildDate>Wed, 04 Oct 2023 13:16:44 -0000</lastBuildDate> + <pubDate>Wed, 04 Oct 2023 13:16:44 -0000</pubDate> <ttl>250</ttl> <atom:link href="https://web.navan.dev/feed.rss" rel="self" type="application/rss+xml"/> @@ -3209,6 +3209,186 @@ logger.info("rdkit-{} installation finished!".format(rdkit.__version__)) <item> <guid isPermaLink="true"> + https://web.navan.dev/posts/2023-10-04-bomb-lab.html + </guid> + <title> + Bomb Lab + </title> + <description> + Introduction, Phase 1 and Phase 2 of Bomb Lab for CSCI 2400 Lab - 2 + </description> + <link>https://web.navan.dev/posts/2023-10-04-bomb-lab.html</link> + <pubDate>Wed, 04 Oct 2023 13:12:00 -0000</pubDate> + <content:encoded><![CDATA[<h1>Bomb Lab</h1> + +<h2>Introduction</h2> + +<p>Lab 2 for CSCI 2400 - Computer Systems. </p> + +<h2>Phase 1</h2> + +<pre><code>jovyan@jupyter-nach6988:~/lab2-bomblab-navanchauhan/bombbomb$ gdb -ex 'break phase_1' -ex 'break explode_bomb' -ex 'run' ./bomb +GNU gdb (Ubuntu 12.1-0ubuntu1~22.04) 12.1 +Copyright (C) 2022 Free Software Foundation, Inc. +License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> +This is free software: you are free to change and redistribute it. +There is NO WARRANTY, to the extent permitted by law. +Type "show copying" and "show warranty" for details. +This GDB was configured as "x86_64-linux-gnu". +Type "show configuration" for configuration details. +For bug reporting instructions, please see: +<https://www.gnu.org/software/gdb/bugs/>. +Find the GDB manual and other documentation resources online at: + <http://www.gnu.org/software/gdb/documentation/>. + +For help, type "help". +Type "apropos word" to search for commands related to "word"... +Reading symbols from ./bomb... +Breakpoint 1 at 0x15c7 +Breakpoint 2 at 0x1d4a +Starting program: /home/jovyan/lab2-bomblab-navanchauhan/bombbomb/bomb +[Thread debugging using libthread_db enabled] +Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". +Welcome to my fiendish little bomb. You have 6 phases with +which to blow yourself up. Have a nice day! +test string + +Breakpoint 1, 0x00005555555555c7 in phase_1 () +(gdb) dias phase_1 +Undefined command: "dias". Try "help". +(gdb) disas phase_1 +Dump of assembler code for function phase_1: +=> 0x00005555555555c7 <+0>: endbr64 + 0x00005555555555cb <+4>: sub $0x8,%rsp + 0x00005555555555cf <+8>: lea 0x1b7a(%rip),%rsi # 0x555555557150 + 0x00005555555555d6 <+15>: call 0x555555555b31 <strings_not_equal> + 0x00005555555555db <+20>: test %eax,%eax + 0x00005555555555dd <+22>: jne 0x5555555555e4 <phase_1+29> + 0x00005555555555df <+24>: add $0x8,%rsp + 0x00005555555555e3 <+28>: ret + 0x00005555555555e4 <+29>: call 0x555555555d4a <explode_bomb> + 0x00005555555555e9 <+34>: jmp 0x5555555555df <phase_1+24> +End of assembler dump. +(gdb) print 0x555555557150 +$1 = 93824992244048 +(gdb) x/1s 0x555555557150 +0x555555557150: "Controlling complexity is the essence of computer programming." +(gdb) +</code></pre> + +<h2>Phase 2</h2> + +<pre><code>Phase 1 defused. How about the next one? +1 2 3 4 5 6 + +Breakpoint 1, 0x00005555555555eb in phase_2 () +(gdb) disas +Dump of assembler code for function phase_2: +=> 0x00005555555555eb <+0>: endbr64 + 0x00005555555555ef <+4>: push %rbp + 0x00005555555555f0 <+5>: push %rbx + 0x00005555555555f1 <+6>: sub $0x28,%rsp + 0x00005555555555f5 <+10>: mov %rsp,%rsi + 0x00005555555555f8 <+13>: call 0x555555555d97 <read_six_numbers> + 0x00005555555555fd <+18>: cmpl $0x0,(%rsp) + 0x0000555555555601 <+22>: js 0x55555555560d <phase_2+34> + 0x0000555555555603 <+24>: mov %rsp,%rbp + 0x0000555555555606 <+27>: mov $0x1,%ebx + 0x000055555555560b <+32>: jmp 0x555555555620 <phase_2+53> + 0x000055555555560d <+34>: call 0x555555555d4a <explode_bomb> + 0x0000555555555612 <+39>: jmp 0x555555555603 <phase_2+24> + 0x0000555555555614 <+41>: add $0x1,%ebx + 0x0000555555555617 <+44>: add $0x4,%rbp + 0x000055555555561b <+48>: cmp $0x6,%ebx + 0x000055555555561e <+51>: je 0x555555555631 <phase_2+70> + 0x0000555555555620 <+53>: mov %ebx,%eax + 0x0000555555555622 <+55>: add 0x0(%rbp),%eax + 0x0000555555555625 <+58>: cmp %eax,0x4(%rbp) + 0x0000555555555628 <+61>: je 0x555555555614 <phase_2+41> + 0x000055555555562a <+63>: call 0x555555555d4a <explode_bomb> + 0x000055555555562f <+68>: jmp 0x555555555614 <phase_2+41> + 0x0000555555555631 <+70>: add $0x28,%rsp + 0x0000555555555635 <+74>: pop %rbx + 0x0000555555555636 <+75>: pop %rbp + 0x0000555555555637 <+76>: ret +End of assembler dump. +(gdb) +</code></pre> + +<pre><code> 0x00005555555555fd <+18>: cmpl $0x0,(%rsp) + 0x0000555555555601 <+22>: js 0x55555555560d <phase_2+34> +... + 0x000055555555560d <+34>: call 0x555555555d4a <explode_bomb> +</code></pre> + +<p>The program first compares if the first number is not 0. If the number is not 0, then the <code>cmpl</code> instruction returns a negative value. The <code>js</code> instruction stands for jump if sign -> causing a jump to the specified address if the sign bit is set. This would result in the explode_bomb function being called.</p> + +<pre><code> 0x0000555555555603 <+24>: mov %rsp,%rbp + 0x0000555555555606 <+27>: mov $0x1,%ebx +</code></pre> + +<p><code>%rsp</code> in x86-64 asm, is the stack pointer i.e. it points to the top of the current stack frame. Since the program just read six numbers, the top of the stack (<code>%rsp</code>) contains the address of the first number.</p> + +<p>By executing <code>mov %rsp,%rbp</code> we are setting the base pointer (<code>%rbp</code>) to point to this address.</p> + +<p>Now, for the second instruction <code>mov $0x1,%ebx</code>, we are initalising the <code>%ebx</code> register with the value 1. Based on the assembly code, you can see that this is being used as a counter/index for the loop.</p> + +<pre><code> 0x000055555555560b <+32>: jmp 0x555555555620 <phase_2+53> +</code></pre> + +<p>The program now jumps to <phase_2+53></p> + +<pre><code> 0x0000555555555620 <+53>: mov %ebx,%eax + 0x0000555555555622 <+55>: add 0x0(%rbp),%eax + 0x0000555555555625 <+58>: cmp %eax,0x4(%rbp) + 0x0000555555555628 <+61>: je 0x555555555614 <phase_2+41> +</code></pre> + +<p>Here, the value from <code>%ebx</code> is copied to the <code>%eax</code> register. For this iteration, the value should be 1.</p> + +<p>Then, the value at the memory location pointed by <code>%rbp</code> is added to the value in <code>%eax</code>. For now, 0 is added (the first number that we read).</p> + +<p><code>cmp %eax,0x4(%rbp)</code> - The instruction compares the value in %eax to the value at the memory address <code>%rbp + 4</code>. Since Integers in this context are stored using a word of memory of 4 bytes, this indicates it checks against the second number in the sequence.</p> + +<p><code>je 0x555555555614 <phase_2+41></code> - The program will jump to <code>phase_2+41</code> if the previous <code>cmp</code> instruction determined the values as equal. </p> + +<pre><code> 0x0000555555555614 <+41>: add $0x1,%ebx + 0x0000555555555617 <+44>: add $0x4,%rbp + 0x000055555555561b <+48>: cmp $0x6,%ebx + 0x000055555555561e <+51>: je 0x555555555631 <phase_2+70> + 0x0000555555555620 <+53>: mov %ebx,%eax + 0x0000555555555622 <+55>: add 0x0(%rbp),%eax + 0x0000555555555625 <+58>: cmp %eax,0x4(%rbp) + 0x0000555555555628 <+61>: je 0x555555555614 <phase_2+41> +</code></pre> + +<p>Here, we can see that the program increments <code>%ebx</code> by 1, adds a 4 byte offset to <code>%rbp</code> (the number we will be matching now), and checks if <code>%ebx</code> is equal to 6. If it is, it breaks the loop and jumps to <code><phase_2+70></code> succesfully finishing this stage.</p> + +<p>Now, given that we know the first two numbers in the sequence are <code>0 1</code>, we can calculate the other numbers by following the pattern of adding the counter and the value of the previous number.</p> + +<p>Thus,</p> + +<ul> +<li>3rd number = 1 (previous value) + 2 = 3</li> +<li>4th number = 3 (prev value) + 3 = 6</li> +<li>5th number = 6 (prev value) + 4 = 10</li> +<li>6th number = 10 (prev value) + 5 = 15</li> +</ul> + +<pre><code>... +Phase 1 defused. How about the next one? +0 1 3 6 10 15 + +Breakpoint 1, 0x00005555555555eb in phase_2 () +(gdb) continue +Continuing. +That's number 2. Keep going! +</code></pre> +]]></content:encoded> + </item> + + <item> + <guid isPermaLink="true"> https://web.navan.dev/posts/2020-11-17-Lets-Encrypt-DuckDns.html </guid> <title> |