linux-kernel - Re: [PATCH] uprobes: ensure that uprobe->offset and ->ref_ctr

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Date:   Tue, 5 May 2020 08:49:04 +0200
From:   Sven Schnelle <svens@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Guo Ren <guoren@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Jann Horn <jannh@...gle.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>,
        Security Officers <security@...nel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Ananth N Mavinakayanahalli <ananth@...ibm.com>,
        Naveen Rao <naveen.n.rao@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH] uprobes: ensure that uprobe->offset and ->ref_ctr_offset
 are properly aligned

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