mailing list of musl libc
 help / color / mirror / code / Atom feed
* [musl] i386 __set_thread_area will crash if the syscall fails
@ 2020-08-31  0:34 Theodore Dubois
  2020-08-31  1:07 ` Rich Felker
  0 siblings, 1 reply; 7+ messages in thread
From: Theodore Dubois @ 2020-08-31  0:34 UTC (permalink / raw)
  To: musl

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

^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2020-09-01 18:20 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-08-31  0:34 [musl] i386 __set_thread_area will crash if the syscall fails Theodore Dubois
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

Code repositories for project(s) associated with this public inbox

	https://git.vuxu.org/mirror/musl/

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).