On Tue, Jan 19, 2016 at 2:18 PM, David Miller <davem@xxxxxxxxxxxxx> wrote: > From: Andy Lutomirski <luto@xxxxxxxxxxxxxx> > Date: Tue, 19 Jan 2016 14:14:43 -0800 > >> On Tue, Jan 19, 2016 at 1:55 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: >>> On Tue, Jan 19, 2016 at 01:47:24PM -0800, Andy Lutomirski wrote: >>>> Essentially all users of is_compat_task in the kernel are trying to >>>> determine whether they are executing in the context of a compat >>>> syscall. On at least x86_64 and sparc, these are not at all the >>>> same question. >>>> >>>> On x86_64 and sparc, therefore, is_compat_task doesn't return the >>>> overall compat state of the task; it returns true if the task is >>>> currently in a compat syscall. >>> >>> The hell it does. Andy, TIF_32BIT is *NOT* set on syscall entry; it is >>> set by execve(). And 64bit task (with that bit clear) can bloody well >>> issue 32bit syscalls. Really. >> >> It does on x86. It does not on sparc. But syscall_get_arch on sparc >> *also* doesn't appear to work right. >> >> davem, how can I check the current syscall bitness on sparc? It's not >> obvious to me that it's possible. > > You have to do it by context if it's important. > What does "by context" mean? This is definitely important for seccomp and audit, and I think it's probably important for other users, too. > In addition to the example Al gave, 32-bit processes can make 64-bit > syscalls too. GDB and other ptrace() using applications can use this > to trace 64-bit programs from 32-bit tracer apps. On x86, is_compat_task returns true in 32-bit syscalls and false in 64-bit syscalls. So a 64-bit task that calls a 32-bit syscall gets is_compat_task. I think that the naming makes no sense whatsoever but that the behavior is actually desirable. If I'm a 32-bit task and I call 64-bit ptrace() [1], I think I want to see the 64-bit siginfo format, not the 32-bit format. A bunch of the drivers that use is_compat_task are specifically trying to distinguish compat from non-compat ioctls. The SPARC is_compat_task implementation doesn't do that. I'm trying to phase out is_compat_task entirely from non-arch code. The WIP version is here: https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/log/?h=in_compat_syscall but it has issues on SPARC. --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
