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 <roger....@citrix.com>
> > ---
> > 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.
Should this go into some kind of buffer which is then printed by
__start_xen() once the console has been initialized? (just after
printing cmdline itself).
Thanks, Roger.
