[S390] user readable uninitialised kernel memory.

A user space program can read uninitialised kernel memory
by appending to a file from a bad address and then reading
the result back. The cause is the copy_from_user function
that does not clear the remaining bytes of the kernel
buffer after it got a fault on the user space address.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 16 insertions, 6 deletions

diff --git a/arch/s390/lib/uaccess_mvcos.c b/arch/s390/lib/uaccess_mvcos.c
index 86c96d6c191a..121b2935a422 100644
--- a/arch/s390/lib/uaccess_mvcos.c
+++ b/arch/s390/lib/uaccess_mvcos.c
@@ -35,7 +35,7 @@ size_t copy_from_user_mvcos(size_t size, const void __user *ptr, void *x)
         tmp1 = -4096UL;
         asm volatile(
                 "0: .insn ss,0xc80000000000,0(%0,%2),0(%1),0\n"
-                "   jz    4f\n"
+                "   jz    7f\n"
                 "1:"ALR"  %0,%3\n"
                 "  "SLR"  %1,%3\n"
                 "  "SLR"  %2,%3\n"
@@ -44,13 +44,23 @@ size_t copy_from_user_mvcos(size_t size, const void __user *ptr, void *x)
                 "   nr    %4,%3\n"      /* %4 = (ptr + 4095) & -4096 */
                 "  "SLR"  %4,%1\n"
                 "  "CLR"  %0,%4\n"      /* copy crosses next page boundary? */
-                "   jnh   5f\n"
+                "   jnh   4f\n"
                 "3: .insn ss,0xc80000000000,0(%4,%2),0(%1),0\n"
                 "  "SLR"  %0,%4\n"
-                "   j     5f\n"
-                "4:"SLR"  %0,%0\n"
-                "5: \n"
-                EX_TABLE(0b,2b) EX_TABLE(3b,5b)
+                "  "ALR"  %2,%4\n"
+                "4:"LHI"  %4,-1\n"
+                "  "ALR"  %4,%0\n"      /* copy remaining size, subtract 1 */
+                "   bras  %3,6f\n"      /* memset loop */
+                "   xc    0(1,%2),0(%2)\n"
+                "5: xc    0(256,%2),0(%2)\n"
+                "   la    %2,256(%2)\n"
+                "6:"AHI"  %4,-256\n"
+                "   jnm   5b\n"
+                "   ex    %4,0(%3)\n"
+                "   j     8f\n"
+                "7:"SLR"  %0,%0\n"
+                "8: \n"
+                EX_TABLE(0b,2b) EX_TABLE(3b,4b)
                 : "+a" (size), "+a" (ptr), "+a" (x), "+a" (tmp1), "=a" (tmp2)
                 : "d" (reg0) : "cc", "memory");
         return size;