On 03/21/2017 10:31 PM, Andy Lutomirski wrote:
On Tue, Mar 21, 2017 at 11:09 AM, Dmitry Safonov <dsafonov@xxxxxxxxxxxxx> wrote:
On 03/21/2017 08:45 PM, Andy Lutomirski wrote:
On Tue, Mar 21, 2017 at 10:17 AM, Cyrill Gorcunov <gorcunov@xxxxxxxxx>
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'm curious: shouldn't x32 CRIU just work? What goes wrong?
I also think, it should be quite easy to add, as we have arch_prctl()
for vdso and etc.
But there are things, which will not work if we just dump application
as 64-bit.
For example, what comes to mind: sys_get_robust_list(), it has different
pointers for 64-bit or for x32/ia32 applications: robust_list
and compat_robust_list. So during C/R we should sometimes call
compatible syscalls for x32 applications to dump/restore, as for futex
list e.g., native will return NULL or empty list.
--Andy
--
Dmitry
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