[PATCH] x86-64: Fix up handling of non canonical user RIPs

EM64T CPUs have somewhat weird error reporting for non canonical RIPs in
SYSRET.

We can't handle any exceptions there because the exception handler would
end up running on the user stack which is unsafe.

To avoid problems any code that might end up with a user touched pt_regs
should return using int_ret_from_syscall.  int_ret_from_syscall ends up
using IRET, which allows safe exceptions.

Cc: Ernie Petrides <petrides@redhat.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S
index 7c10e9009d611173d13fddf90650a9dfe78ec7db..22cb6ee074b91994df738b77e17aa8ca93cf7b58 100644 (file)
--- a/arch/x86_64/kernel/entry.S
+++ b/arch/x86_64/kernel/entry.S
@@ -178,6 +178,12 @@ rff_trace:
  * Interrupts are off on entry.
  * Only called from user space.
  *
+ * EM64T CPUs have somewhat weird error reporting for non canonical RIPs in SYSRET. 
+ * We can't handle any exceptions there because the exception handler would
+ * end up running on the user stack which is unsafe. To avoid problems 
+ * any code that might end up with a user touched pt_regs should return
+ * using int_ret_from_syscall.
+ *
  * XXX if we had a free scratch register we could save the RSP into the stack frame
  *      and report it properly in ps. Unfortunately we haven't.
  */                                    
@@ -254,7 +260,9 @@ sysret_signal:
        xorl %esi,%esi # oldset -> arg2
        call ptregscall_common
 1:     movl $_TIF_NEED_RESCHED,%edi
-       jmp sysret_check
+       /* Stack frame might have been changed. The IRET path does
+          some additional checks to handle this */
+       jmp int_with_check
        
 badsys:
        movq $-ENOSYS,RAX-ARGOFFSET(%rsp)
@@ -280,7 +288,8 @@ tracesys:
        call syscall_trace_leave
        RESTORE_TOP_OF_STACK %rbx
        RESTORE_REST
-       jmp ret_from_sys_call
+       /* Stack frame might have been changed. Use the more careful IRET path */
+       jmp int_ret_from_sys_call
        CFI_ENDPROC
                
 /* 
@@ -408,25 +417,9 @@ ENTRY(stub_execve)
        CFI_ADJUST_CFA_OFFSET -8
        CFI_REGISTER rip, r11
        SAVE_REST
-       movq %r11, %r15
-       CFI_REGISTER rip, r15
        FIXUP_TOP_OF_STACK %r11
        call sys_execve
-       GET_THREAD_INFO(%rcx)
-       bt $TIF_IA32,threadinfo_flags(%rcx)
-       CFI_REMEMBER_STATE
-       jc exec_32bit
        RESTORE_TOP_OF_STACK %r11
-       movq %r15, %r11
-       CFI_REGISTER rip, r11
-       RESTORE_REST
-       pushq %r11
-       CFI_ADJUST_CFA_OFFSET 8
-       CFI_REL_OFFSET rip, 0
-       ret
-
-exec_32bit:
-       CFI_RESTORE_STATE
        movq %rax,RAX(%rsp)
        RESTORE_REST
        jmp int_ret_from_sys_call