From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
xen-devel@lists.xenproject.org, ross.lagerwall@citrix.com
Subject: Re: [PATCH v4 7/9] livepatch: NOP if func->new_[addr] is zero.
Date: Tue, 6 Sep 2016 16:05:38 -0400 [thread overview]
Message-ID: <20160906200538.GB32099@char.us.oracle.com> (raw)
In-Reply-To: <57BD814E0200007800108843@prv-mh.provo.novell.com>
On Wed, Aug 24, 2016 at 03:13:18AM -0600, Jan Beulich wrote:
> >>> On 24.08.16 at 04:22, <konrad.wilk@oracle.com> wrote:
> > The NOP functionality will NOP any of the code at
> > the 'old_addr' or at 'name' if the 'new_addr' is zero.
> > The purpose of this is to NOP out calls, such as:
> >
> > e8 <4-bytes-offset>
> >
> > (5 byte insn), or on ARM a 4 byte insn for branching.
> > But on x86 we could NOP instructions that are much
> > shorter or longer (up to 15 bytes).
>
> And we could NOP multiple instructions in one go, i.e. the new
> boundary you introduce is still arbitrary.
True.
I am limited by the 'struct livepatch_func' -> opaque[31] size.
I figured an OK limit would be up to a maximum platform instruction size.
That is what the design document mentions too:
" then `new_size` determines how many instruction bytes to NOP (up to
platform limitations)."
But in reality it could be up to 31 bytes - unless I rework the 'opaque'
to have a void pointer to some bigger size structure - but if I do that
then this gets complicated.
Keep in mind that the person writting the payload can have multiple
'struct livepatch_func' - so you could NOP a stream of say 30 bytes
using two 'struct livepatch_func'.
If we allow the NOP to be up to the size of the 'opaque' size, then
you could NOP a stream of instructions up to 62 bytes with two
'struct livepatch_func'. or such. Thought to keep this from blowing
up on ARM I would say it has to be up to modulo 4.
Do you have a preference on this?
>
> Jan
>
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next prev parent reply other threads:[~2016-09-06 20:05 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-24 2:22 [PATCH v4] Livepatch fixes and features for v4.8 Konrad Rzeszutek Wilk
2016-08-24 2:22 ` [PATCH v4 1/9] livepatch: Clear .bss when payload is reverted Konrad Rzeszutek Wilk
2016-08-24 8:55 ` Jan Beulich
2016-08-25 16:08 ` Andrew Cooper
2016-09-06 16:51 ` Konrad Rzeszutek Wilk
2016-09-07 9:18 ` Jan Beulich
2016-09-06 16:47 ` Konrad Rzeszutek Wilk
2016-09-07 8:02 ` Jan Beulich
2016-09-08 9:25 ` Konrad Rzeszutek Wilk
2016-09-09 13:33 ` Ross Lagerwall
2016-09-09 13:50 ` Konrad Rzeszutek Wilk
2016-09-09 13:58 ` Ross Lagerwall
2016-09-09 15:28 ` Jan Beulich
2016-08-24 2:22 ` [PATCH v4 2/9] livepatch: Deal with payloads without any .text Konrad Rzeszutek Wilk
2016-08-24 2:22 ` [PATCH v4 3/9] version/livepatch: Move xen_build_id_check to version.h Konrad Rzeszutek Wilk
2016-08-24 2:22 ` [PATCH v4 4/9] version: Print build-id at bootup Konrad Rzeszutek Wilk
2016-08-24 8:58 ` Jan Beulich
2016-09-06 16:57 ` Konrad Rzeszutek Wilk
2016-09-07 8:03 ` Jan Beulich
2016-09-09 13:37 ` Ross Lagerwall
2016-08-24 2:22 ` [PATCH v4 5/9] livepatch: Move code from prepare_payload to own routine Konrad Rzeszutek Wilk
2016-08-25 16:02 ` Ross Lagerwall
2016-08-24 2:22 ` [PATCH v4 6/9] livepatch: Add parsing for the symbol+0x<offset> Konrad Rzeszutek Wilk
2016-08-24 9:08 ` Jan Beulich
2016-09-06 19:56 ` Konrad Rzeszutek Wilk
2016-09-07 8:10 ` Jan Beulich
2016-09-08 9:22 ` Konrad Rzeszutek Wilk
2016-09-08 10:01 ` Jan Beulich
2016-09-09 14:28 ` Ross Lagerwall
2016-08-24 2:22 ` [PATCH v4 7/9] livepatch: NOP if func->new_[addr] is zero Konrad Rzeszutek Wilk
2016-08-24 9:13 ` Jan Beulich
2016-09-06 20:05 ` Konrad Rzeszutek Wilk [this message]
2016-09-07 8:13 ` Jan Beulich
2016-08-24 2:22 ` [PATCH v4 8/9] symbols: Generate an xen-sym.map Konrad Rzeszutek Wilk
2016-08-24 9:16 ` Jan Beulich
2016-09-09 13:43 ` Ross Lagerwall
2016-08-24 2:22 ` [PATCH v4 9/9] livepach: Add .livepatch.hooks functions and test-case Konrad Rzeszutek Wilk
2016-09-06 17:22 ` Konrad Rzeszutek Wilk
2016-09-06 18:25 ` Andrew Cooper
2016-09-08 1:18 ` Konrad Rzeszutek Wilk
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