On Fri, Feb 13, 2015 at 04:56:29PM -0500, Chris Metcalf wrote: > On 2/13/2015 5:44 AM, Catalin Marinas wrote: > >On Fri, Feb 13, 2015 at 04:00:43PM +0800, Bamvor Jian Zhang wrote: > >>diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c > >>index e299de396e9b..32601939a3c8 100644 > >>--- a/arch/arm64/kernel/signal32.c > >>+++ b/arch/arm64/kernel/signal32.c > >>@@ -154,8 +154,7 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from) > >> case __SI_TIMER: > >> err |= __put_user(from->si_tid, &to->si_tid); > >> err |= __put_user(from->si_overrun, &to->si_overrun); > >>- err |= __put_user((compat_uptr_t)(unsigned long)from->si_ptr, > >>- &to->si_ptr); > >>+ err |= __put_user(from->si_int, &to->si_int); > >> break; > >> case __SI_POLL: > >> err |= __put_user(from->si_band, &to->si_band); > >>@@ -184,7 +183,7 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from) > >> case __SI_MESGQ: /* But this is */ > >> err |= __put_user(from->si_pid, &to->si_pid); > >> err |= __put_user(from->si_uid, &to->si_uid); > >>- err |= __put_user((compat_uptr_t)(unsigned long)from->si_ptr, &to->si_ptr); > >>+ err |= __put_user(from->si_int, &to->si_int); > >> break; > >> case __SI_SYS: > >> err |= __put_user((compat_uptr_t)(unsigned long) > > I must be confused here, but I don't see that these do anything different. > > If we are writing 32 bits to to->si_ptr or to->si_int, either way the high 32 bits > are irrelevant. So whether we read it from from->si_ptr and massage the high bits, > or just read it from from->si_int as a straight-up 32-bit quantity, either way it > seems we should end up writing the same bits to userspace. > > I would understand the argument if we were overlaying the si_ptr/si_int union > from a kernel-side siginfo_t where si_ptr and si_int are different sizes > onto userspace, but it doesn't seem we ever do that. That's the problem, "from" above is a kernel siginfo_t while "to" is a compat_siginfo_t. The call paths go something like: 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. A similar example is sys_timer_create() which takes a sigevent argument. Maybe Bamvor has a test case. (btw, I'm off for a week, I'll follow up when I get back) -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
