Post AEhwRkWGJUsRC7xtom by robey@mastodon.technology
 (DIR) More posts by robey@mastodon.technology
 (DIR) Post #AEhwRjVs3SyC4cm4ZM by brion@mastodon.technology
       2021-12-23T20:13:15Z
       
       0 likes, 0 repeats
       
       can you just mmap something in at page 0 and own the NULL pointer? or does the operating system prevent that
       
 (DIR) Post #AEhwRjyaKhwFVgD0KG by brion@mastodon.technology
       2021-12-23T20:30:02Z
       
       0 likes, 0 repeats
       
       macos doesn't seem to let me do a fixed mapping at null, it returns ENOMEM :D
       
 (DIR) Post #AEhwRkWGJUsRC7xtom by robey@mastodon.technology
       2021-12-23T20:52:38Z
       
       0 likes, 0 repeats
       
       @brion (rusty but) on some systems, dark-mapping 0 - 1MB is *how* null pointer traps happen
       
 (DIR) Post #AEhwRlojUJFJDhcAFM by mansr@society.oftrolls.com
       2021-12-23T21:19:36Z
       
       0 likes, 0 repeats
       
       @robey @brion I have done it in the past for debugging purposes, but I think modern systems disallow it, at least by default. It's a reasonable precaution, IMHO.
       
 (DIR) Post #AEhyd3JYyQJea3XiD2 by penguin42@mastodon.org.uk
       2021-12-23T21:44:05Z
       
       0 likes, 0 repeats
       
       @brion I think most architectures used to allow that;  Linux added a low mapping limit to stop it;  it's better to have stuff crash if they accidentally dereference NULL rather than access potentially attacker controlled data.