[Devel] [PATCH vz7] x86,ia32: Restore 32bit personality

[Cyrill Gorcunov]

When restoring compatible applications (ie running in ia32
mode) we have to restore thread flags and mm context at
least otherwise compat_alloc_user_space may allocate
values from old_rsp remembered at last 64 bit syscall
leading to EFAULT.

Note the vanilla kernel already switched to pt_regs::sp
for this sake but backporting the patch is not an
option due to its size.

In the patch we simply make sure that the task is in
container and has no TIF_IA32 before thus when CRIU
call for rt_sigreturn via int80 gate we adjust the
flags needed.

 | [root at pcs7 ~]# vzctl exec b3a8161f-50e2-4072-ab0a-93baa9ac20d4 cat /home/criu/test/zdtm/static/aio01.out
 | 15:08:15.525:   201: tail=2, head=128, nr=255
 | 15:08:26.424:   201: tail=2, head=128, nr=255
 | 15:08:26.425:   201: tail=3, head=128, nr=255
 | 15:08:26.425:   201: PASS

Previously this test failed because after the
restore we call for io_submit in the test and
kernel tries to allocate helper structure to
convert arguments from compat to native mode
with compat_alloc_user_space and failed.

https://jira.sw.ru/browse/PSBM-76965

CC: Andrei Vagin <avagin at openvz.org>
CC: Dmitry Safonov <0x7f454c46 at gmail.com>
CC: Pavel Emelyanov <xemul at virtuozzo.com>
CC: Kirill Tkhai <ktkhai at virtuozzo.com>
CC: Konstantin Khorenko <khorenko at virtuozzo.com>
Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
---
 arch/x86/ia32/ia32_signal.c |   53 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

Index: linux-pcs7.git/arch/x86/ia32/ia32_signal.c
===================================================================
--- linux-pcs7.git.orig/arch/x86/ia32/ia32_signal.c
+++ linux-pcs7.git/arch/x86/ia32/ia32_signal.c
@@ -35,6 +35,10 @@
 #include <asm/sys_ia32.h>
 #include <asm/smap.h>
 
+#ifdef CONFIG_VE
+# include <linux/ve.h>
+#endif
+
 void sigaction_compat_abi(struct k_sigaction *act, struct k_sigaction *oact)
 {
 	/* Don't leak in-kernel non-uapi flags to user-space */
@@ -258,6 +262,53 @@ badframe:
 	return 0;
 }
 
+#ifdef CONFIG_VE
+extern int force_personality32;
+
+static void ve_set_personality_ia32(struct pt_regs *regs)
+{
+	if (ve_is_super(current->task_ve) ||
+	    test_thread_flag(TIF_IA32))
+		return;
+
+	/*
+	 * TIF_IA32 flag is used by the kernel to figure out
+	 * the task address space at least but more importantly
+	 * in compat_alloc_user_space when an application is
+	 * doing syscalls like io_submit and etc. So when
+	 * we restore such process via rt_sigreturn syscall
+	 * from inside of native mode with int80 gate help
+	 * we have to restore the TIF_IA32 and ia32_compat
+	 * at least.
+	 *
+	 * NOTE 1: this applies to applications running inside
+	 * VE only. The vanilla kernel alreasy throwing off
+	 * old_rsp symbol but the patch is too big to merge
+	 * inside.
+	 *
+	 * NOTE 2: this is pretty valid to call int80 on
+	 * regular x86-64 bit application with rt_sigreturn
+	 * as syscall number, but it's rather an exception
+	 * than common practice (except CRIU of course).
+	 */
+	if (regs->cs == __USER32_CS) {
+		/*
+		 * It's close to set_personality_ia32
+		 * but we don't want to change orig_ax.
+		 */
+		set_thread_flag(TIF_ADDR32);
+		set_thread_flag(TIF_IA32);
+		clear_thread_flag(TIF_X32);
+		current->personality |= force_personality32;
+		current_thread_info()->status |= TS_COMPAT;
+		if (current->mm)
+			current->mm->context.ia32_compat = TIF_IA32;
+	}
+}
+#else
+static void ve_set_personality_ia32(struct pt_regs *regs) { }
+#endif
+
 asmlinkage long sys32_rt_sigreturn(void)
 {
 	struct pt_regs *regs = current_pt_regs();
@@ -277,6 +328,8 @@ asmlinkage long sys32_rt_sigreturn(void)
 	if (ia32_restore_sigcontext(regs, &frame->uc.uc_mcontext, &ax))
 		goto badframe;
 
+	ve_set_personality_ia32(regs);
+
 	if (compat_restore_altstack(&frame->uc.uc_stack))
 		goto badframe;