On 23/02/2024 10:17 am, Roger Pau Monné wrote:
> On Fri, Feb 23, 2024 at 09:46:27AM +0000, Andrew Cooper wrote:
>> On 23/02/2024 9:42 am, Roger Pau Monne wrote:
>>> The current logic to handle the BRANCH_HARDEN option will report it as
>>> enabled
>>> even when build-time disabled. Fix this by only allowing the option to be
>>> set
>>> when support for it is built into Xen.
>>>
>>> Fixes: 2d6f36daa086 ('x86/nospec: Introduce
>>> CONFIG_SPECULATIVE_HARDEN_BRANCH')
>>> Signed-off-by: Roger Pau Monné <[email protected]>
>>> ---
>>> xen/arch/x86/spec_ctrl.c | 6 ++++--
>>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
>>> index 421fe3f640df..e634c6b559b4 100644
>>> --- a/xen/arch/x86/spec_ctrl.c
>>> +++ b/xen/arch/x86/spec_ctrl.c
>>> @@ -50,7 +50,8 @@ static int8_t __initdata opt_psfd = -1;
>>> int8_t __ro_after_init opt_ibpb_ctxt_switch = -1;
>>> int8_t __read_mostly opt_eager_fpu = -1;
>>> int8_t __read_mostly opt_l1d_flush = -1;
>>> -static bool __initdata opt_branch_harden = true;
>>> +static bool __initdata opt_branch_harden =
>>> + IS_ENABLED(CONFIG_SPECULATIVE_HARDEN_BRANCH);
>>>
>>> bool __initdata bsp_delay_spec_ctrl;
>>> uint8_t __read_mostly default_xen_spec_ctrl;
>>> @@ -267,7 +268,8 @@ static int __init cf_check parse_spec_ctrl(const char
>>> *s)
>>> opt_eager_fpu = val;
>>> else if ( (val = parse_boolean("l1d-flush", s, ss)) >= 0 )
>>> opt_l1d_flush = val;
>>> - else if ( (val = parse_boolean("branch-harden", s, ss)) >= 0 )
>>> + else if ( IS_ENABLED(CONFIG_SPECULATIVE_HARDEN_BRANCH) &&
>>> + (val = parse_boolean("branch-harden", s, ss)) >= 0 )
>>> opt_branch_harden = val;
>> Yeah, we should definitely fix this, but could we use no_config_param()
>> here for the compiled-out case ?
>>
>> See cet= for an example. If we're going to ignore what the user asks,
>> we should tell them why.
> Maybe I'm missing something: I've looked into using no_config_param(),
> but there's no difference really, because cmdline_parse() is called
> before the console is initialized, so those messages seem to be
> lost.
Look at `xl dmesg` rather than the console. They also do appear on vga
in some configurations.
There's a separate todo to get these out in a slightly nicer way, but
they at least exist in logs.
~Andrew
