On Tue, Jan 17, 2012 at 8:56 AM, Will Drewry <wad@xxxxxxxxxxxx> wrote: > On Tue, Jan 17, 2012 at 10:45 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: >> On 01/16, Will Drewry wrote: >>> >>> On Mon, Jan 16, 2012 at 12:37 PM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: >>> > >>> > Yes, thanks, I forgot about compat tasks again. But this is easy, just >>> > we need regs_64_to_32(). >>> >>> Yup - we could make the assumption that is_compat_task is always >>> 32-bit and the pt_regs is always 64-bit, then copy_and_truncate with >>> regs_64_to_32. Seems kinda wonky though :/ >> >> much simpler/faster than what regset does to create the artificial >> user_regs_struct32. > > True, I could collapse pt_regs to looks like the exported ABI pt_regs. > Then only compat processes would get the copy overhead. That could > be tidy and not break ABI. It would mean that I have to assume that > if unsigned long == 64-bit and is_compat_task(), then the task is > 32-bit. Do you think if we ever add a crazy 128-bit "supercomputer" > arch that we will add a is_compat64_task() so that I could properly > collapse? :) > > I like this idea! FWIW, it's possible for a task to execute in 32-bit mode when !is_compat_task or in 64-bit mode when is_compat_task. From earlier in the thread, I think you were planning to block the wrong-bitness syscall entries, but it's worth double-checking that you don't open up a hole when a compat task issues the 64-bit syscall instruction. (is_compat_task says whether the executable was marked as 32-bit. The actual execution mode is determined by the cs register, which the user can control. See the user_64bit_mode function in arch/asm/x86/ptrace.h. But maybe it would make more sense to have a separate 32-bit and 64-bit BPF program and select which one to use based on the entry point.) --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
