powerpc/mm: Don't log user reads to 0xffffffff

Running vdsotest leaves many times the following log:

  [   79.629901] vdsotest[396]: User access of kernel address (ffffffff) - exploit attempt? (uid: 0)

A pointer set to (-1) is likely a programming error similar to
a NULL pointer and is not worth logging as an exploit attempt.

Don't log user accesses to 0xffffffff.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/0728849e826ba16f1fbd6fa7f5c6cc87bd64e097.1577087627.git.christophe.leroy@c-s.fr

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 9e119f98a7250598dfb45a386bde5dc445f39191..7534ee5bf9b26c15b5f948a9bd9e6c8e70a104a4 100644 (file)
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -350,6 +350,9 @@ static void sanity_check_fault(bool is_write, bool is_user,
         * Userspace trying to access kernel address, we get PROTFAULT for that.
         */
        if (is_user && address >= TASK_SIZE) {
+               if ((long)address == -1)
+                       return;
+
                pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n",
                                   current->comm, current->pid, address,
                                   from_kuid(&init_user_ns, current_uid()));