[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, 26 insertions, 10 deletions

diff --git a/arch/s390/lib/uaccess_std.c b/arch/s390/lib/uaccess_std.c
index 9a4d4a29ea79..f44f0078b354 100644
--- a/arch/s390/lib/uaccess_std.c
+++ b/arch/s390/lib/uaccess_std.c
@@ -35,25 +35,35 @@ size_t copy_from_user_std(size_t size, const void __user *ptr, void *x)
         tmp1 = -256UL;
         asm volatile(
                 "0: mvcp  0(%0,%2),0(%1),%3\n"
-                "   jz    5f\n"
+                "   jz    8f\n"
                 "1:"ALR"  %0,%3\n"
                 "   la    %1,256(%1)\n"
                 "   la    %2,256(%2)\n"
                 "2: mvcp  0(%0,%2),0(%1),%3\n"
                 "   jnz   1b\n"
-                "   j     5f\n"
+                "   j     8f\n"
                 "3: la    %4,255(%1)\n" /* %4 = ptr + 255 */
                 "  "LHI"  %3,-4096\n"
                 "   nr    %4,%3\n"      /* %4 = (ptr + 255) & -4096 */
                 "  "SLR"  %4,%1\n"
                 "  "CLR"  %0,%4\n"      /* copy crosses next page boundary? */
-                "   jnh   6f\n"
+                "   jnh   5f\n"
                 "4: mvcp  0(%4,%2),0(%1),%3\n"
                 "  "SLR"  %0,%4\n"
-                "   j     6f\n"
-                "5:"SLR"  %0,%0\n"
-                "6: \n"
-                EX_TABLE(0b,3b) EX_TABLE(2b,3b) EX_TABLE(4b,6b)
+                "  "ALR"  %2,%4\n"
+                "5:"LHI"  %4,-1\n"
+                "  "ALR"  %4,%0\n"      /* copy remaining size, subtract 1 */
+                "   bras  %3,7f\n"      /* memset loop */
+                "   xc    0(1,%2),0(%2)\n"
+                "6: xc    0(256,%2),0(%2)\n"
+                "   la    %2,256(%2)\n"
+                "7:"AHI"  %4,-256\n"
+                "   jnm   6b\n"
+                "   ex    %4,0(%3)\n"
+                "   j     9f\n"
+                "8:"SLR"  %0,%0\n"
+                "9: \n"
+                EX_TABLE(0b,3b) EX_TABLE(2b,3b) EX_TABLE(4b,5b)
                 : "+a" (size), "+a" (ptr), "+a" (x), "+a" (tmp1), "=a" (tmp2)
                 : : "cc", "memory");
         return size;
@@ -67,16 +77,22 @@ size_t copy_from_user_std_small(size_t size, const void __user *ptr, void *x)
         asm volatile(
                 "0: mvcp  0(%0,%2),0(%1),%3\n"
                 "  "SLR"  %0,%0\n"
-                "   j     3f\n"
+                "   j     5f\n"
                 "1: la    %4,255(%1)\n" /* %4 = ptr + 255 */
                 "  "LHI"  %3,-4096\n"
                 "   nr    %4,%3\n"      /* %4 = (ptr + 255) & -4096 */
                 "  "SLR"  %4,%1\n"
                 "  "CLR"  %0,%4\n"      /* copy crosses next page boundary? */
-                "   jnh   3f\n"
+                "   jnh   5f\n"
                 "2: mvcp  0(%4,%2),0(%1),%3\n"
                 "  "SLR"  %0,%4\n"
-                "3:\n"
+                "  "ALR"  %2,%4\n"
+                "3:"LHI"  %4,-1\n"
+                "  "ALR"  %4,%0\n"      /* copy remaining size, subtract 1 */
+                "   bras  %3,4f\n"
+                "   xc    0(1,%2),0(%2)\n"
+                "4: ex    %4,0(%3)\n"
+                "5:\n"
                 EX_TABLE(0b,1b) EX_TABLE(2b,3b)
                 : "+a" (size), "+a" (ptr), "+a" (x), "+a" (tmp1), "=a" (tmp2)
                 : : "cc", "memory");