Re: [PATCH] uprobes: ensure that uprobe->offset and ->ref_ctr_offset are properly aligned

[Sven Schnelle <svens@linux.ibm.com>]

Hi,

On Mon, May 04, 2020 at 08:40:44PM +0200, Christian Borntraeger wrote:
> 
> 
> On 04.05.20 18:47, Oleg Nesterov wrote:
> > 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.
> 
> I think the idea was that the uprobe instruction is 2 bytes and instructions
> are always aligned to 2 bytes on s390.  (we can have 2,4 or 6 bytes).
> 
> > 
> > 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.
> 
> Not sure if it would have been possible to try to create a uprobe on an 
> odd address. If yes, then the new IS_ALIGNED check certainly makes this
> better for s390, so the patch looks sane. Adding Vasily and Sven to double
> check.

I did a quick test, and without this patch it is possible to place a uprobe
at an odd address. With the patch it fails with EINVAL, which is more
reasonable.

Regards
Sven