From: Theodore Dubois <tblodt@icloud.com>
To: musl@lists.openwall.com
Subject: [musl] i386 __set_thread_area will crash if the syscall fails
Date: Sun, 30 Aug 2020 17:34:09 -0700 [thread overview]
Message-ID: <3C00D395-838B-4DB0-99FC-3947F1BCF054@icloud.com> (raw)
Found a (small) bug in this file: https://git.musl-libc.org/cgit/musl/tree/src/thread/i386/__set_thread_area.s
If the syscall fails, the branch on line 20 is taken and %eax will be a small negative number. Then "mov $123,%al" will make syscall 0xffffff7b instead of 0x7b, since overwriting %al only overwrites the low byte of %eax. So the modify_ldt fallback has apparently never worked.
Tangentially, I'm not sure why this file has so many hardcoded magic numbers and no comments to explain what they are.
~Theodore
next reply other threads:[~2020-08-31 1:01 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-31 0:34 Theodore Dubois [this message]
2020-08-31 1:07 ` Rich Felker
2020-08-31 1:41 ` Rich Felker
2020-08-31 2:51 ` Rich Felker
2020-09-01 18:20 ` Markus Wichmann
2020-08-31 6:55 ` Alexander Monakov
2020-08-31 12:36 ` Rich Felker
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