[PATCH] uml: skas0 stubs now check system call return values

Change syscall-stub's data to include a "expected retval".

Stub now checks syscalls retval and aborts execution of syscall list, if
retval != expected retval.

run_syscall_stub prints the data of the failed syscall, using the data pointer
and retval written by the stub to the beginning of the stack.

one_syscall_stub is removed, to simplify code, because only some instructions
are saved by one_syscall_stub, no host-syscall.

Using the stub with additional data (modify_ldt via stub)
is prepared also.

Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 40 insertions, 10 deletions

diff --git a/arch/um/sys-x86_64/stub.S b/arch/um/sys-x86_64/stub.S
index 957f2eff32ca..03c279735784 100644
--- a/arch/um/sys-x86_64/stub.S
+++ b/arch/um/sys-x86_64/stub.S
@@ -16,21 +16,51 @@ syscall_stub:
 
         .globl batch_syscall_stub
 batch_syscall_stub:
-        movq    $(UML_CONFIG_STUB_DATA >> 32), %rbx
-        salq    $32, %rbx
-        movq    $(UML_CONFIG_STUB_DATA & 0xffffffff), %rcx
-        or      %rcx, %rbx
-        movq    %rbx, %rsp
-again:  pop     %rax
-        cmpq    $0, %rax
-jz      done
+        mov     $(UML_CONFIG_STUB_DATA >> 32), %rbx
+        sal     $32, %rbx
+        mov     $(UML_CONFIG_STUB_DATA & 0xffffffff), %rax
+        or      %rax, %rbx
+        /* load pointer to first operation */
+        mov     %rbx, %rsp
+        add     $0x10, %rsp
+again:
+        /* load length of additional data */
+        mov     0x0(%rsp), %rax
+
+        /* if(length == 0) : end of list */
+        /* write possible 0 to header */
+        mov     %rax, 8(%rbx)
+        cmp     $0, %rax
+        jz      done
+
+        /* save current pointer */
+        mov     %rsp, 8(%rbx)
+
+        /* skip additional data */
+        add     %rax, %rsp
+
+        /* load syscall-# */
+        pop     %rax
+
+        /* load syscall params */
         pop     %rdi
         pop     %rsi
         pop     %rdx
         pop     %r10
         pop     %r8
         pop     %r9
+
+        /* execute syscall */
         syscall
+
+        /* check return value */
+        pop     %rcx
+        cmp     %rcx, %rax
+        je      again
+
+done:
+        /* save return value */
         mov     %rax, (%rbx)
-        jmp     again
-done:   int3
+
+        /* stop */
+        int3