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:4.215 / U:0.244 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site