Re: [PATCH 04/13] xen/arm: Add ARCH_WORKAROUND_2 probing

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 25/05/2018 21:51, Stefano Stabellini wrote:
> On Wed, 23 May 2018, Julien Grall wrote:
>> Hi,
>>
>> On 05/23/2018 10:57 PM, Stefano Stabellini wrote:
>>> On Tue, 22 May 2018, Julien Grall wrote:
>>>> As for Spectre variant-2, we rely on SMCCC 1.1 to provide the discovery
>>>> mechanism for detecting the SSBD mitigation.
>>>>
>>>> A new capability is also allocated for that purpose, and a config
>>>> option.
>>>>
>>>> This is part of XSA-263.
>>>>
>>>> Signed-off-by: Julien Grall <julien.grall@arm.com>
>>>> ---
>>>>   xen/arch/arm/Kconfig             | 10 ++++++++++
>>>>   xen/arch/arm/cpuerrata.c         | 39
>>>> +++++++++++++++++++++++++++++++++++++++
>>>>   xen/include/asm-arm/cpuerrata.h  | 21 +++++++++++++++++++++
>>>>   xen/include/asm-arm/cpufeature.h |  3 ++-
>>>>   xen/include/asm-arm/smccc.h      |  6 ++++++
>>>>   5 files changed, 78 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
>>>> index 8174c0c635..0e2d027060 100644
>>>> --- a/xen/arch/arm/Kconfig
>>>> +++ b/xen/arch/arm/Kconfig
>>>> @@ -73,6 +73,16 @@ config SBSA_VUART_CONSOLE
>>>>   	  Allows a guest to use SBSA Generic UART as a console. The
>>>>   	  SBSA Generic UART implements a subset of ARM PL011 UART.
>>>>   +config ARM_SSBD
>>>> +	bool "Speculative Store Bypass Disable" if EXPERT = "y"
>>>> +	depends on HAS_ALTERNATIVE
>>>> +	default y
>>>> +	help
>>>> +	  This enables mitigation of bypassing of previous stores by
>>>> speculative
>>>> +	  loads.
>>> I would add a reference to spectre v4. What do you think of:
>>>
>>>    This enables the mitigation of Spectre v4 attacks based on bypassing
>>>    of previous memory stores by speculative loads.
>> Well, the real name is SSBD (Speculative Store Bypass Disable). AFAIK, Spectre
>> only refers to variant 1 and 2 so far. This one has no fancy name and the
>> specifications is using SSBD.
> Googling for Spectre Variant 4 returns twice as many results as Googling
> for Speculative Store Bypass Disable. It doesn't matter what is the
> official name for the security issue, I think we need to include a
> reference to the most common name for it.

"Speculative Store Bypass" is the agreed vendor-neutral name for the
issue.  This is why all the mitigation is SSBD, where the D on the end
is Disable.

Google SP4 is a common name (but only covers one reporter of the issue),
whereas Spectre has nothing to do with this issue, and is definitely
wrong to use.

If in doubt, use SSB(D).

~Andrew

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