linux-kernel - Re: [PATCH V2 13/15] selftests/sgx: Add page permission and exception test

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Date:   Fri, 29 Oct 2021 06:08:12 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Reinette Chatre <reinette.chatre@...el.com>
Cc:     linux-sgx@...r.kernel.org, shuah@...nel.org,
        dave.hansen@...ux.intel.com, seanjc@...gle.com,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 13/15] selftests/sgx: Add page permission and
 exception test

On Thu, Oct 28, 2021 at 01:37:38PM -0700, Reinette Chatre wrote:
> The Enclave Page Cache Map (EPCM) is a secure structure used by the
> processor to track the contents of the enclave page cache. The EPCM
> contains permissions with which enclave pages can be accessed. SGX
> support allows EPCM and PTE page permissions to differ - as long as
> the PTE permissions do not exceed the EPCM permissions.
> 
> Add a test that:
> (1) Creates an SGX enclave page with writable EPCM permission.
> (2) Changes the PTE permission on the page to read-only. This should
>     be permitted because the permission does not exceed the EPCM
>     permission.
> (3) Attempts a write to the page. This should generate a page fault
>     (#PF) because of the read-only PTE even though the EPCM
>     permissions allow the page to be written to.
> 
> This introduces the first test of SGX exception handling. In this test
> the issue that caused the exception (PTE page permissions) can be fixed
> from outside the enclave and after doing so it is possible to re-enter
> enclave at original entrypoint with ERESUME.
> 
> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>

Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>

/Jarkko