lkml.org 
[lkml]   [2022]   [Feb]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH 14/29] x86/ibt: Add IBT feature, MSR and #CP handling
On Fri, Feb 18, 2022 at 07:31:38PM +0000, Andrew Cooper wrote:
> On 18/02/2022 16:49, Peter Zijlstra wrote:
> > --- a/arch/x86/kernel/cpu/common.c
> > +++ b/arch/x86/kernel/cpu/common.c
> > @@ -592,6 +593,27 @@ static __init int setup_disable_pku(char
> > __setup("nopku", setup_disable_pku);
> > #endif /* CONFIG_X86_64 */
> >
> > +static __always_inline void setup_cet(struct cpuinfo_x86 *c)
> > +{
> > + u64 msr;
> > +
> > + if (!IS_ENABLED(CONFIG_X86_IBT) ||
> > + !cpu_feature_enabled(X86_FEATURE_IBT))
> > + return;
> > +
> > + cr4_set_bits(X86_CR4_CET);
> > +
> > + rdmsrl(MSR_IA32_S_CET, msr);
> > + if (cpu_feature_enabled(X86_FEATURE_IBT))
> > + msr |= CET_ENDBR_EN;
> > + wrmsrl(MSR_IA32_S_CET, msr);
>
> So something I learnt the hard way with shstk is that you really want to
> disable S_CET before heading into purgatory.
>
> I've got no idea what's going to result from UEFI finally getting CET
> support.  However, clearing out the other IBT settings is probably a
> wise move.
>
> In particular, if there was a stale legacy bitmap pointer, then
> ibt_selftest() could take #PF ahead of #CP.

How's this then? That writes the whole state to a known value before
enabling CR4.CET to make the thing go...

+static __always_inline void setup_cet(struct cpuinfo_x86 *c)
+{
+ u64 msr = CET_ENDBR_EN;
+
+ if (!IS_ENABLED(CONFIG_X86_IBT) ||
+ !cpu_feature_enabled(X86_FEATURE_IBT))
+ return;
+
+ wrmsrl(MSR_IA32_S_CET, msr);
+ cr4_set_bits(X86_CR4_CET);
+
+ if (!ibt_selftest()) {
+ pr_err("IBT selftest: Failed!\n");
+ setup_clear_cpu_cap(X86_FEATURE_IBT);
+ }
+}

\
 
 \ /
  Last update: 2022-02-18 22:15    [W:0.203 / U:0.504 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site