CET-IBT depend on executing indirect branches for protections to apply. Extend the clobber for CET-SS to all of CET.
Signed-off-by: Andrew Cooper <[email protected]> --- CC: Jan Beulich <[email protected]> CC: Roger Pau Monné <[email protected]> CC: Wei Liu <[email protected]> I can't decide if this wants a fixes tag or not. If I'd remembered during the CET series, it would have been its own patch. Functionally, it depends on c/s cdbe2b0a1aec which sets CR4.CET fairly early during boot. --- xen/arch/x86/spec_ctrl.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c index 2d4cf5c7ef80..12bf1c5722f9 100644 --- a/xen/arch/x86/spec_ctrl.c +++ b/xen/arch/x86/spec_ctrl.c @@ -944,10 +944,11 @@ void __init init_speculation_mitigations(void) boot_cpu_has(X86_FEATURE_IBRS)); /* - * First, disable the use of retpolines if Xen is using shadow stacks, as - * they are incompatible. + * First, disable the use of retpolines if Xen is using CET. Retpolines + * are a ROP gadget so incompatbile with Shadow Stacks, while IBT depends + * on executing indirect branches for the safety properties to apply. */ - if ( cpu_has_xen_shstk && + if ( (read_cr4() & X86_CR4_CET) && (opt_thunk == THUNK_DEFAULT || opt_thunk == THUNK_RETPOLINE) ) thunk = THUNK_JMP; -- 2.11.0
