x86_64: Zero extend all registers after ptrace in 32bit entry path.

Strictly it's only needed for eax.

It actually does a little more than strictly needed -- the other registers
are already zero extended.

Also remove the now unnecessary and non functional compat task check
in ptrace.

This is CVE-2007-4573

Found by Wojciech Purczynski
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/x86_64/ia32/ia32entry.S

@@ -38,6 +38,18 @@
 	movq	%rax,R8(%rsp)
 	.endm
 
+	.macro LOAD_ARGS32 offset
+	movl \offset(%rsp),%r11d
+	movl \offset+8(%rsp),%r10d
+	movl \offset+16(%rsp),%r9d
+	movl \offset+24(%rsp),%r8d
+	movl \offset+40(%rsp),%ecx
+	movl \offset+48(%rsp),%edx
+	movl \offset+56(%rsp),%esi
+	movl \offset+64(%rsp),%edi
+	movl \offset+72(%rsp),%eax
+	.endm
+	
 	.macro CFI_STARTPROC32 simple
 	CFI_STARTPROC	\simple
 	CFI_UNDEFINED	r8
@@ -152,7 +164,7 @@ sysenter_tracesys:
 	movq	$-ENOSYS,RAX(%rsp)	/* really needed? */
 	movq	%rsp,%rdi        /* &pt_regs -> arg1 */
 	call	syscall_trace_enter
-	LOAD_ARGS ARGOFFSET  /* reload args from stack in case ptrace changed it */
+	LOAD_ARGS32 ARGOFFSET  /* reload args from stack in case ptrace changed it */
 	RESTORE_REST
 	movl	%ebp, %ebp
 	/* no need to do an access_ok check here because rbp has been
@@ -255,7 +267,7 @@ cstar_tracesys:
 	movq $-ENOSYS,RAX(%rsp)	/* really needed? */
 	movq %rsp,%rdi        /* &pt_regs -> arg1 */
 	call syscall_trace_enter
-	LOAD_ARGS ARGOFFSET  /* reload args from stack in case ptrace changed it */
+	LOAD_ARGS32 ARGOFFSET  /* reload args from stack in case ptrace changed it */
 	RESTORE_REST
 	movl RSP-ARGOFFSET(%rsp), %r8d
 	/* no need to do an access_ok check here because r8 has been
@@ -334,7 +346,7 @@ ia32_tracesys:
 	movq $-ENOSYS,RAX(%rsp)	/* really needed? */
 	movq %rsp,%rdi        /* &pt_regs -> arg1 */
 	call syscall_trace_enter
-	LOAD_ARGS ARGOFFSET  /* reload args from stack in case ptrace changed it */
+	LOAD_ARGS32 ARGOFFSET  /* reload args from stack in case ptrace changed it */
 	RESTORE_REST
 	jmp ia32_do_syscall
 END(ia32_syscall)

arch/x86_64/kernel/ptrace.c

@@ -232,10 +232,6 @@ static int putreg(struct task_struct *child,
 {
 	unsigned long tmp; 
 	
-	/* Some code in the 64bit emulation may not be 64bit clean.
-	   Don't take any chances. */
-	if (test_tsk_thread_flag(child, TIF_IA32))
-		value &= 0xffffffff;
 	switch (regno) {
 		case offsetof(struct user_regs_struct,fs):
 			if (value && (value & 3) != 3)