On Wed, Nov 4, 2015 at 4:50 PM, Amanieu d'Antras <amanieu@xxxxxxxxx> wrote: > One issue that isn't resolved in this series is sending signals between a 32-bit > process and 64-bit process. Sending a si_int will work correctly, but a si_ptr > value will likely get corrupted due to the different layouts of the 32-bit and > 64-bit siginfo_t structures. This is so screwed up it's not even funny. A 64-bit big-endian compat calls rt_sigqueueinfo. It passes in (among other things) a sigval_t. The kernel can choose to interpret it as a pointer (call it p) or an integer (call it i). Then (unsigned long)p = (i<<32) | [something]. If the number was an integer to begin with *and* user code zeroed out the mess first, then [something] will be 0. Regardless, p != i unless they're both zero. If the result gets delivered to a signalfd, then it's plausible that everything could work. If it gets delivered to a 64-bit siginfo, then all is well because it's in exactly the same screwed up state it was in when the signal gets sent. If, however, it's delivered to a compat task, wtf is the kernel supposed to do? We're effectively supposed to convert a 64-bit sigval_t to a 32-bit sigval_t. On a little-endian architecture, we can fudge it because it doesn't really matter whether we consider the pointer or the int to be authoritative. I think that, on big-endian, we're screwed. BTW, x86 has its own set of screwups here. Somehow cr2 and error_code ended up as part of ucontext instead of siginfo, which makes absolutely no sense to me and bloats task_struct. --Andy -- 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
