linux-kernel - Re: Subject: [PATCH 0/1] SGX self test fails

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Date:   Mon, 3 May 2021 09:39:05 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     Tim Gardner <tim.gardner@...onical.com>,
        dave.hansen@...ux.intel.com, shuah@...nel.org,
        linux-sgx@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Subject: [PATCH 0/1] SGX self test fails

On 5/3/21 8:41 AM, Jarkko Sakkinen wrote:
>> $ ls -l /dev/sgx_enclave
>> crw------- 1 dave dave 10, 125 Apr 28 11:32 /dev/sgx_enclave
>> $ ./test_sgx
>> 0x0000000000000000 0x0000000000002000 0x03
>> 0x0000000000002000 0x0000000000001000 0x05
>> 0x0000000000003000 0x0000000000003000 0x03
>> SUCCESS
>>
>> *But*, is that OK?  Should we be happily creating a PROT_EXEC mapping on
>> a ugo-x file?  Why were we respecting noexec on the filesystem but not
>> ugo-x on the file?
> Yeah, this supports my earlier response:
> 
> "EPERM  The prot argument asks for PROT_EXEC but the mapped area
>  belongs to a file on a filesystem that was mounted no-exec."
> https://man7.org/linux/man-pages/man2/mmap.2.html
> 
> I guess the right model is to think just as "anonymous memory"
> with equivalent access control semantics after succesfully
> opened for read and write.

I guess I'll answer my own question: The "x" bit on file permissions
really only controls the ability for the file to be execve()'d, but has
no bearing on the ability for an executable *mapping* to be created.
This is existing VFS behavior and is not specific to SGX.

I think I'll just send a patch to pull that warning out.