From: Jarkko Sakkinen <jarkko@kernel.org>
To: Reinette Chatre <reinette.chatre@intel.com>,
Shuah Khan <shuah@kernel.org>
Cc: linux-sgx@vger.kernel.org, nathaniel@profian.com,
Dave Hansen <dave.hansen@linux.intel.com>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] selftests/sgx: Use rip relative addressing for encl_stack
Date: Thu, 31 Mar 2022 03:59:07 +0300 [thread overview]
Message-ID: <c1ab42d56309bb06c0e64daf204570f06585bddc.camel@kernel.org> (raw)
In-Reply-To: <3aa93449-6951-8085-f6a1-6739b6d515d9@intel.com>
On Wed, 2022-03-30 at 17:10 -0700, Reinette Chatre wrote:
> Hi Jarkko,
>
> On 3/30/2022 3:28 PM, Jarkko Sakkinen wrote:
> > Simplify the test_encl_bootstrap.S flow by using RIP-relative addressing.
>
> It is not clear to me how this is simpler. At this point there is no
> functional change (except for what appears to be an unintended bug - more below).
> At this time the change seems more code utilizing subtle compiler features
> to accomplish the same.
>
> Could you please share more about your plans following this change? I need
> to understand this better since it is also an area changed by the SGX2 testing
> code.
>
> > The compiler automatically puts relative addresses for RIP index addresses.
>
> I was not aware of this. A comment would be helpful to understand the implementation.
>
> >
> > In order to get a clean and tweakless solution, define separate entry point
> > for each TCS.
> >
> > Cc: Reinette Chatre <reinette.chatre@intel.com>
> > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> > ---
> > v2:
> > * Based on Reinette's example, make proper structuring with separate
> > entry points for each TCS.
> > ---
> > .../selftests/sgx/test_encl_bootstrap.S | 30 +++++++++++--------
> > 1 file changed, 18 insertions(+), 12 deletions(-)
> >
> > diff --git a/tools/testing/selftests/sgx/test_encl_bootstrap.S b/tools/testing/selftests/sgx/test_encl_bootstrap.S
> > index 82fb0dfcbd23..cc2353f38bcc 100644
> > --- a/tools/testing/selftests/sgx/test_encl_bootstrap.S
> > +++ b/tools/testing/selftests/sgx/test_encl_bootstrap.S
> > @@ -10,12 +10,13 @@
> > .section ".tcs", "aw"
> > .balign 4096
> >
> > +encl_tcs1:
> > .fill 1, 8, 0 # STATE (set by CPU)
> > .fill 1, 8, 0 # FLAGS
> > .quad encl_ssa_tcs1 # OSSA
> > .fill 1, 4, 0 # CSSA (set by CPU)
> > .fill 1, 4, 1 # NSSA
> > - .quad encl_entry # OENTRY
> > + .quad encl_entry1 # OENTRY
> > .fill 1, 8, 0 # AEP (set by EENTER and ERESUME)
> > .fill 1, 8, 0 # OFSBASE
> > .fill 1, 8, 0 # OGSBASE
> > @@ -23,13 +24,13 @@
> > .fill 1, 4, 0xFFFFFFFF # GSLIMIT
> > .fill 4024, 1, 0 # Reserved
> >
> > - # TCS2
> > +encl_tcs2:
> > .fill 1, 8, 0 # STATE (set by CPU)
> > .fill 1, 8, 0 # FLAGS
> > .quad encl_ssa_tcs2 # OSSA
> > .fill 1, 4, 0 # CSSA (set by CPU)
> > .fill 1, 4, 1 # NSSA
> > - .quad encl_entry # OENTRY
> > + .quad encl_entry2 # OENTRY
> > .fill 1, 8, 0 # AEP (set by EENTER and ERESUME)
> > .fill 1, 8, 0 # OFSBASE
> > .fill 1, 8, 0 # OGSBASE
> > @@ -39,15 +40,19 @@
> >
> > .text
> >
> > -encl_entry:
> > - # RBX contains the base address for TCS, which is the first address
> > - # inside the enclave for TCS #1 and one page into the enclave for
> > - # TCS #2. By adding the value of encl_stack to it, we get
> > - # the absolute address for the stack.
> > - lea (encl_stack)(%rbx), %rax
> > +encl_entry1:
> > + lea (encl_stack1)(%rip), %rax
> > xchg %rsp, %rax
> > push %rax
> > + jmp encl_continue
> >
> > +encl_entry2:
> > + lea (encl_stack2)(%rip), %rax
> > + xchg %rsp, %rax
> > + push %rax
> > + jmp encl_continue
> > +
>
> The code duplication (xchg and push) is not needed.
>
> > +encl_continue:
> > push %rcx # push the address after EENTER
> > push %rbx # push the enclave base address
> >
> > @@ -84,13 +89,14 @@ encl_entry:
> >
> > encl_ssa_tcs1:
> > .space 4096
> > +
> > encl_ssa_tcs2:
> > .space 4096
> >
> > +encl_stack1:
>
> Stack grows the other way so by placing the entry here the stack of
> TCS #1 will clobber the SSA of TCS #2.
>
> > .balign 4096
> > - # Stack of TCS #1
> > .space 4096
> > -encl_stack:
> > +
> > +encl_stack2:
>
> Here the stack of TCS #2 will actually use the stack of TCS #1.
>
> > .balign 4096
> > - # Stack of TCS #2
> > .space 4096
>
> Last page will be unused.
>
> Reinette
Thanks for the remarks. I'll fix the issues.
BR, Jarkko
prev parent reply other threads:[~2022-03-31 0:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-30 22:28 [PATCH v2] selftests/sgx: Use rip relative addressing for encl_stack Jarkko Sakkinen
2022-03-31 0:10 ` Reinette Chatre
2022-03-31 0:59 ` Jarkko Sakkinen [this message]
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