uprobes: ensure that uprobe->offset and ->ref_ctr_offset are properly aligned

uprobe_write_opcode() must not cross page boundary; prepare_uprobe()
relies on arch_uprobe_analyze_insn() which should validate "vaddr" but
some architectures (csky, s390, and sparc) don't do this.

We can remove the BUG_ON() check in prepare_uprobe() and validate the
offset early in __uprobe_register(). The new IS_ALIGNED() check matches
the alignment check in arch_prepare_kprobe() on supported architectures,
so I think that all insns must be aligned to UPROBE_SWBP_INSN_SIZE.

Another problem is __update_ref_ctr() which was wrong from the very
beginning, it can read/write outside of kmap'ed page unless "vaddr" is
aligned to sizeof(short), __uprobe_register() should check this too.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Sven Schnelle <svens@linux.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index e51ec844c87cc29d6ed4872cdc3e31363e9041ef..5dc2f46f38c065e5306c1b199b35a05a77b9b6f8 100644 (file)
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -861,10 +861,6 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
        if (ret)
                goto out;
 
-       /* uprobe_write_opcode() assumes we don't cross page boundary */
-       BUG_ON((uprobe->offset & ~PAGE_MASK) +
-                       UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
-
        smp_wmb(); /* pairs with the smp_rmb() in handle_swbp() */
        set_bit(UPROBE_COPY_INSN, &uprobe->flags);
 
@@ -1160,6 +1156,15 @@ static int __uprobe_register(struct inode *inode, loff_t offset,
        if (offset > i_size_read(inode))
                return -EINVAL;
 
+       /*
+        * This ensures that copy_from_page(), copy_to_page() and
+        * __update_ref_ctr() can't cross page boundary.
+        */
+       if (!IS_ALIGNED(offset, UPROBE_SWBP_INSN_SIZE))
+               return -EINVAL;
+       if (!IS_ALIGNED(ref_ctr_offset, sizeof(short)))
+               return -EINVAL;
+
  retry:
        uprobe = alloc_uprobe(inode, offset, ref_ctr_offset);
        if (!uprobe)
@@ -2008,6 +2013,9 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr)
        uprobe_opcode_t opcode;
        int result;
 
+       if (WARN_ON_ONCE(!IS_ALIGNED(vaddr, UPROBE_SWBP_INSN_SIZE)))
+               return -EINVAL;
+
        pagefault_disable();
        result = __get_user(opcode, (uprobe_opcode_t __user *)vaddr);
        pagefault_enable();