On Tue, Feb 24, 2015 at 04:54:17PM -0500, Chris Metcalf wrote:
On 2/14/2015 6:22 AM, Catalin Marinas wrote:
quoted
1. user populates sival_int compat_sigevent and invokes
compat_sys_mq_notify()
2. kernel get_compat_sigevent() copies compat_sigevent into the native
sigevent. compat and native sival_int are the same, no problem so
far. The other half of 64-bit sival_ptr is zeroed by a memset in this
function (this other half can be top or bottom, depending on
endianness)
3. signal is about to be delivered to user via arch code. The
compat_ptr(from->si_ptr) conversion always takes the least
significant part of the native si_ptr. On big endian 64-bit, this is
zero because get_compat_sigevent() populated the top part of si_ptr
with si_int.
So delivering such signals to compat user always sets si_int to 0.
Little endian is fine.
I looked at this again as I was getting ready to do a tile patch, and realized
why tile and arm64 are different here: tile does a field-by-field copy in
copy_siginfo_from_user32(), like parisc and s390. As a result, we initialize
the 64-bit kernel si_ptr value by cast from the 32-bit user si_ptr value, rather
than blindly writing into the lower-addressed half of the 64-bit sigval.
It's not about copy_siginfo_from_user32() but the generic
get_compat_sigevent() which always uses sival_int (called from e.g.
compat_sys_timer_create()).
--
Catalin