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 <[email protected]>
Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Oleg Nesterov <[email protected]>
Reviewed-by: Srikar Dronamraju <[email protected]>
Acked-by: Christian Borntraeger <[email protected]>
Tested-by: Sven Schnelle <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: [email protected]
Signed-off-by: Linus Torvalds <[email protected]>

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