x86 vDSO: ia32 sysenter_return

This changes the 64-bit kernel's support for the 32-bit sysenter
instruction to use stored fields rather than constants for the
user-mode return address, as the 32-bit kernel does.  This adds a
sysenter_return field to struct thread_info, as 32-bit has.  There
is no observable effect from this yet.  It makes the assembly code
independent of the 32-bit vDSO mapping address, paving the way for
making the vDSO address vary as it does on the 32-bit kernel.

[ akpm@linux-foundation.org: build fix on !CONFIG_IA32_EMULATION ]
Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/ia32/ia32entry.S

@@ -12,7 +12,6 @@
 #include <asm/ia32_unistd.h>	
 #include <asm/thread_info.h>	
 #include <asm/segment.h>
-#include <asm/vsyscall32.h>
 #include <asm/irqflags.h>
 #include <linux/linkage.h>
 
@@ -104,7 +103,7 @@ ENTRY(ia32_sysenter_target)
 	pushfq
 	CFI_ADJUST_CFA_OFFSET 8
 	/*CFI_REL_OFFSET rflags,0*/
-	movl	$VSYSCALL32_SYSEXIT, %r10d
+	movl	8*3-THREAD_SIZE+threadinfo_sysenter_return(%rsp), %r10d
 	CFI_REGISTER rip,r10
 	pushq	$__USER32_CS
 	CFI_ADJUST_CFA_OFFSET 8
@@ -142,6 +141,8 @@ sysenter_do_call:
 	andl    $~TS_COMPAT,threadinfo_status(%r10)
 	/* clear IF, that popfq doesn't enable interrupts early */
 	andl  $~0x200,EFLAGS-R11(%rsp) 
+	movl	RIP-R11(%rsp),%edx		/* User %eip */
+	CFI_REGISTER rip,rdx
 	RESTORE_ARGS 1,24,1,1,1,1
 	popfq
 	CFI_ADJUST_CFA_OFFSET -8
@@ -149,8 +150,6 @@ sysenter_do_call:
 	popq	%rcx				/* User %esp */
 	CFI_ADJUST_CFA_OFFSET -8
 	CFI_REGISTER rsp,rcx
-	movl	$VSYSCALL32_SYSEXIT,%edx	/* User %eip */
-	CFI_REGISTER rip,rdx
 	TRACE_IRQS_ON
 	swapgs
 	sti		/* sti only takes effect after the next instruction */

arch/x86/ia32/syscall32.c

@@ -46,6 +46,10 @@ int syscall32_setup_pages(struct linux_binprm *bprm, int exstack)
 				      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
 				      VM_ALWAYSDUMP,
 				      syscall32_pages);
+	if (ret == 0) {
+		current->mm->context.vdso = (void __user *)VSYSCALL32_BASE;
+		current_thread_info()->sysenter_return = VSYSCALL32_SYSEXIT;
+	}
 	up_write(&mm->mmap_sem);
 	return ret;
 }

arch/x86/kernel/asm-offsets_64.c

@@ -46,6 +46,9 @@ int main(void)
 	ENTRY(addr_limit);
 	ENTRY(preempt_count);
 	ENTRY(status);
+#ifdef CONFIG_IA32_EMULATION
+	ENTRY(sysenter_return);
+#endif
 	BLANK();
 #undef ENTRY
 #define ENTRY(entry) DEFINE(pda_ ## entry, offsetof(struct x8664_pda, entry))

include/asm-x86/thread_info_64.h

@@ -33,6 +33,9 @@ struct thread_info {
 
 	mm_segment_t		addr_limit;	
 	struct restart_block    restart_block;
+#ifdef CONFIG_IA32_EMULATION
+	void __user		*sysenter_return;
+#endif
 };
 #endif