[edk2-devel] [PATCH] OvmfPkg/README: HTTPS Boot: describe host-side TLS cipher suites forwarding

Thu Sep 10 06:02:56 UTC 2020

On 09/09/20 18:21, Philippe Mathieu-Daudé wrote:
> On 9/7/20 6:18 PM, Laszlo Ersek wrote:
>> In QEMU commit range 4abf70a661a5..69699f3055a5, Phil implemented a QEMU
>> facility for exposing the host-side TLS cipher suite configuration to
>> OVMF. The purpose is to control the permitted ciphers in the guest's UEFI
>> HTTPS boot. This complements the forwarding of the host-side crypto policy
>> from the host to the guest -- the other facet was the set of CA
>> certificates (for which p11-kit patches had been upstreamed, on the host
>> side).
>>
>> Mention the new command line options in "OvmfPkg/README".
>>
>> Cc: Ard Biesheuvel <ard.biesheuvel at arm.com>
>> Cc: Gary Lin <glin at suse.com>
>> Cc: Jordan Justen <jordan.l.justen at intel.com>
>> Cc: Philippe Mathieu-Daudé <philmd at redhat.com>
>> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2852
> 
> Thanks for addressing this BZ for me...
> 
>> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
>> ---
>>  OvmfPkg/README | 24 ++++++++++++--------
>>  1 file changed, 15 insertions(+), 9 deletions(-)
>>
>> diff --git a/OvmfPkg/README b/OvmfPkg/README
>> index 3dd28474ead4..2009d9d29796 100644
>> --- a/OvmfPkg/README
>> +++ b/OvmfPkg/README
>> @@ -294,67 +294,73 @@ and encrypted connection.
>>  
>>    You can also append a certificate to the existing list with the following
>>    command:
>>  
>>    efisiglist -i <old certdb> -a <cert file> -o <new certdb>
>>  
>>    NOTE: You may need the patch to make efisiglist generate the correct header.
>>    (https://github.com/rhboot/pesign/pull/40)
>>  
>>  * Besides the trusted certificates, it's also possible to configure the trusted
>>    cipher suites for HTTPS through another fw_cfg entry: etc/edk2/https/ciphers.
>>  
>> -  -fw_cfg name=etc/edk2/https/ciphers,file=<cipher suites>
>> -
>>    OVMF expects a binary UINT16 array which comprises the cipher suites HEX
>>    IDs(*4). If the cipher suite list is given, OVMF will choose the cipher
>>    suite from the intersection of the given list and the built-in cipher
>>    suites. Otherwise, OVMF just chooses whatever proper cipher suites from the
>>    built-in ones.
>>  
>> -  While the tool(*5) to create the cipher suite array is still under
>> -  development, the array can be generated with the following script:
>> +  Using QEMU 5.1 or later, QEMU can expose the ordered list of permitted TLS
>> +  cipher suites from the host side to OVMF:
>> +
>> +  -object tls-cipher-suites,id=mysuite0,priority=@SYSTEM \
>> +  -fw_cfg name=etc/edk2/https/ciphers,gen_id=mysuite0
>> +
>> +  (Refer to the QEMU manual and to
>> +  <https://gnutls.org/manual/html_node/Priority-Strings.html> for more
>> +  information on the "priority" property.)
>> +
>> +  Using QEMU 5.0 or earlier, the array has to be passed from a file:
> 
> What about using a '-' to list each "Using QEMU ..." and make the
> separation clearer?

I can do that, yes. There are three possibilities:

- prefix just one line (in each affected paragraph) with the hyphen,

- prefix the first line of each paragraph with the hyphen, plus indent
the rest of the *same paragraph* by 2 spaces.

- prefix the first line of each paragraph with the hyphen, plus indent
the rest of the *text* that applies to the QEMU versions being discussed.

Which one do you prefer?

Thanks,
Laszlo

> 
> Regardless:
> Reviewed-by: Philippe Mathieu-Daude <philmd at redhat.com>
> Tested-by: Philippe Mathieu-Daude <philmd at redhat.com>
> 
>> +
>> +  -fw_cfg name=etc/edk2/https/ciphers,file=<cipher suites>
>> +
>> +  whose contents can be generated with the following script, for example:
>>  
>>    export LC_ALL=C
>>    openssl ciphers -V \
>>    | sed -r -n \
>>       -e 's/^ *0x([0-9A-F]{2}),0x([0-9A-F]{2}) - .*$/\\\\x\1 \\\\x\2/p' \
>>    | xargs -r -- printf -- '%b' > ciphers.bin
>>  
>>    This script creates ciphers.bin that contains all the cipher suite IDs
>>    supported by openssl according to the local host configuration.
>>  
>>    You may want to enable only a limited set of cipher suites. Then, you
>>    should check the validity of your list first:
>>  
>>    openssl ciphers -V <cipher list>
>>  
>>    If all the cipher suites in your list map to the proper HEX IDs, go ahead
>>    to modify the script and execute it:
>>  
>>    export LC_ALL=C
>>    openssl ciphers -V <cipher list> \
>>    | sed -r -n \
>>       -e 's/^ *0x([0-9A-F]{2}),0x([0-9A-F]{2}) - .*$/\\\\x\1 \\\\x\2/p' \
>>    | xargs -r -- printf -- '%b' > ciphers.bin
>>  
>> -* In the future (after release 2.12), QEMU should populate both above fw_cfg
>> -  files automatically from the local host configuration, and enable the user
>> -  to override either with dedicated options or properties.
>> -
>>  (*1) See "31.4.1 Signature Database" in UEFI specification 2.7 errata A.
>>  (*2) p11-kit: https://github.com/p11-glue/p11-kit/
>>  (*3) efisiglist: https://github.com/rhboot/pesign/blob/master/src/efisiglist.c
>>  (*4) https://wiki.mozilla.org/Security/Server_Side_TLS#Cipher_names_correspondence_table
>> -(*5) update-crypto-policies: https://gitlab.com/redhat-crypto/fedora-crypto-policies
>>  
>>  === OVMF Flash Layout ===
>>  
>>  Like all current IA32/X64 system designs, OVMF's firmware device (rom/flash)
>>  appears in QEMU's physical address space just below 4GB (0x100000000).
>>  
>>  OVMF supports building a 1MB, 2MB or 4MB flash image (see the DSC files for the
>>  FD_SIZE_1MB, FD_SIZE_2MB, FD_SIZE_4MB build defines). The base address for the
>>  1MB image in QEMU physical memory is 0xfff00000. The base address for the 2MB
>>  image is 0xffe00000. The base address for the 4MB image is 0xffc00000.
>>  
>>  Using the 1MB or 2MB image, the layout of the firmware device in memory looks
>>
> 

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