summaryrefslogtreecommitdiffstats
path: root/mm
diff options
context:
space:
mode:
authorDavid Miller <davem@davemloft.net>2007-11-12 23:59:05 -0800
committerGreg Kroah-Hartman <gregkh@suse.de>2007-11-16 08:12:44 -0800
commit59ddd4607313e7ee20b9ad36cd3b00f83068189a (patch)
tree77fd71150f40dc1939e71f2bdc5783a67b60e9af /mm
parente823c33c6f670beba3c14f4a451fd2b34c3eb40c (diff)
downloadlinux-stable-59ddd4607313e7ee20b9ad36cd3b00f83068189a.tar.gz
linux-stable-59ddd4607313e7ee20b9ad36cd3b00f83068189a.tar.bz2
linux-stable-59ddd4607313e7ee20b9ad36cd3b00f83068189a.zip
Fix compat futex hangs.
[FUTEX]: Fix address computation in compat code. [ Upstream commit: 3c5fd9c77d609b51c0bab682c9d40cbb496ec6f1 ] compat_exit_robust_list() computes a pointer to the futex entry in userspace as follows: (void __user *)entry + futex_offset 'entry' is a 'struct robust_list __user *', and 'futex_offset' is a 'compat_long_t' (typically a 's32'). Things explode if the 32-bit sign bit is set in futex_offset. Type promotion sign extends futex_offset to a 64-bit value before adding it to 'entry'. This triggered a problem on sparc64 running 32-bit applications which would lock up a cpu looping forever in the fault handling for the userspace load in handle_futex_death(). Compat userspace runs with address masking (wherein the cpu zeros out the top 32-bits of every effective address given to a memory operation instruction) so the sparc64 fault handler accounts for this by zero'ing out the top 32-bits of the fault address too. Since the kernel properly uses the compat_uptr interfaces, kernel side accesses to compat userspace work too since they will only use addresses with the top 32-bit clear. Because of this compat futex layer bug we get into the following loop when executing the get_user() load near the top of handle_futex_death(): 1) load from address '0xfffffffff7f16bd8', FAULT 2) fault handler clears upper 32-bits, processes fault for address '0xf7f16bd8' which succeeds 3) goto #1 I want to thank Bernd Zeimetz, Josip Rodin, and Fabio Massimo Di Nitto for their tireless efforts helping me track down this bug. Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'mm')
0 files changed, 0 insertions, 0 deletions