Messages in this thread | | | Subject | Re: [PATCHv2] x86/mm: set x32 syscall bit in SET_PERSONALITY() | From | Dmitry Safonov <> | Date | Tue, 21 Mar 2017 21:09:40 +0300 |
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On 03/21/2017 08:45 PM, Andy Lutomirski wrote: > On Tue, Mar 21, 2017 at 10:17 AM, Cyrill Gorcunov <gorcunov@gmail.com> wrote: >> On Tue, Mar 21, 2017 at 07:37:12PM +0300, Dmitry Safonov wrote: >> ... >>> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c >>> index d6b784a5520d..d3d4d9abcaf8 100644 >>> --- a/arch/x86/kernel/process_64.c >>> +++ b/arch/x86/kernel/process_64.c >>> @@ -519,8 +519,14 @@ void set_personality_ia32(bool x32) >>> if (current->mm) >>> current->mm->context.ia32_compat = TIF_X32; >>> current->personality &= ~READ_IMPLIES_EXEC; >>> - /* in_compat_syscall() uses the presence of the x32 >>> - syscall bit flag to determine compat status */ >>> + /* >>> + * in_compat_syscall() uses the presence of the x32 >>> + * syscall bit flag to determine compat status. >>> + * On the bitness of syscall relies x86 mmap() code, >>> + * so set x32 syscall bit right here to make >>> + * in_compat_syscall() work during exec(). >>> + */ >>> + task_pt_regs(current)->orig_ax |= __X32_SYSCALL_BIT; >>> current->thread.status &= ~TS_COMPAT; >> >> Hi! I must admit I didn't follow close the overall series (so can't >> comment much here :) but I have a slightly unrelated question -- is >> there a way to figure out if task is running in x32 mode say with >> some ptrace or procfs sign? > > You should be able to figure out of a *syscall* is x32 by simply > looking at bit 30 in the syscall number. (This is unlike i386, which > is currently not reflected in ptrace.)
The process could be stopped with PTRACE_SEIZE and I think, it'll not have x32 syscall bit at that moment.
I guess the question comes from that we're releasing CRIU 3.0 with 32-bit C/R and some other cool stuff, but we don't support x32 yet. As we don't want release a thing that we aren't properly testing. So for a while we should error on dumping x32 applications.
I think, the best way for now is to check physicall address of vdso from /proc/.../pagemap. If it's CONFIG_VDSO=n kernel, I guess we could also add check for %ds from ptrace's register set. For x32 it's set to __USER_DS, while for native it's 0 (looking at start_thread() and compat_start_thread()). The application can simply change it without any consequence - so it's not very reliable, we could only warn at catching it, not rely on this.
> > Do we actually have an x32 per-task mode at all? If so, maybe we can > just remove it on top of Dmitry's series.
-- Dmitry
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