From: Jarkko Sakkinen <jarkko@kernel.org>
To: Reinette Chatre <reinette.chatre@intel.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Shuah Khan <shuah@kernel.org>,
"open list:INTEL SGX" <linux-sgx@vger.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 1/2] selftests/sgx: Use rip relative addressing for encl_stack
Date: Thu, 31 Mar 2022 01:30:08 +0300 [thread overview]
Message-ID: <cc2c191065c489eb22bb15bf3dd2e3cddc822543.camel@kernel.org> (raw)
In-Reply-To: <595369cd-b7d4-985c-a7e0-7110ffe9a606@intel.com>
On Wed, 2022-03-30 at 14:29 -0700, Reinette Chatre wrote:
> Hi Jarkko,
>
> On 3/30/2022 1:40 PM, Jarkko Sakkinen wrote:
> > On Wed, 2022-03-30 at 13:05 -0700, Reinette Chatre wrote:
> > >
> > >
> > > On 3/30/2022 12:03 PM, Jarkko Sakkinen wrote:
> > > > On Wed, 2022-03-30 at 10:40 -0700, Reinette Chatre wrote:
> > > > > Could you please elaborate how the compiler will fix it up?
> > > >
> > > > Sure.
> > > >
> > > > Here's the disassembly of the RBX version:
> > > >
> > > > [0x000021a9]> pi 1
> > > > lea rax, [rbx + loc.encl_stack]
> > > >
> > > > Here's the same with s/RBX/RIP/:
> > > >
> > > > [0x000021a9]> pi 5
> > > > lea rax, loc.encl_stack
> > > >
> > > > Compiler will substitute correct offset relative to the RIP,
> > > > well, because it can and it makes sense.
> > >
> > > It does not make sense to me because, as proven with my test,
> > > the two threads end up sharing the same stack memory.
> >
> > I see, I need to correct my patch, thanks!
> >
> > RBX gives correct results because of the binary organization,
> > i.e. TCS's are placed to zero offset and forward, and
> > unrelocated symbol is just compiled in as an untranslated
> > offset.
> >
> > RPI is given correct results but how the semantics work
> > right now is incompatible.
> >
> > Still, even for kselftest, I would consider a switch
> > because that way:
> >
> > 1. You can layout binary however you wan and things
> > won't break.
> > 2. You can point to any symbol not just stack, if
> > ever need.
> >
> > I admit it works semantically but it just super
> > unrobust.
>
> I do not think that we need an exceptionally flexible
> runtime as part of the SGX selftests but instead something
> that is easy(*) to understand while also sufficient to support
> the tests.
>
> Reinette
>
> * I do not actually consider the existing enclave test binary
> easy to understand (this thread is proof) but keeping its
> complexity to be minimal would benefit folks needing to
> ramp up on SGX and/or debug kselftest failures.
Based on you feedback I refined the patch:
https://lore.kernel.org/linux-sgx/20220330222834.139769-1-jarkko@kernel.org/T/#u
BR, Jarkko
BR, Jarkko
prev parent reply other threads:[~2022-03-30 22:31 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-22 7:43 [PATCH v2 1/2] selftests/sgx: Use rip relative addressing for encl_stack Jarkko Sakkinen
2022-03-22 7:43 ` [PATCH v2 2/2] selftests/sgx: Make TCS table relocatable Jarkko Sakkinen
2022-03-28 21:49 ` [PATCH v2 1/2] selftests/sgx: Use rip relative addressing for encl_stack Reinette Chatre
2022-03-30 14:54 ` Jarkko Sakkinen
2022-03-30 14:56 ` Jarkko Sakkinen
2022-03-30 17:40 ` Reinette Chatre
[not found] ` <f68d472877b7136c32d8770603a3de38de59c322.camel@kernel.org>
2022-03-30 19:22 ` Jarkko Sakkinen
2022-03-30 20:05 ` Reinette Chatre
2022-03-30 20:40 ` Jarkko Sakkinen
2022-03-30 21:29 ` Reinette Chatre
2022-03-30 22:30 ` Jarkko Sakkinen [this message]
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