From 351428de6feee3769a0ba69fdab3f521be85e891 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Mon, 28 Feb 2022 19:26:37 +0000 Subject: [PATCH] x86/spec-ctrl: Disable retpolines with CET-IBT 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 Reviewed-by: Jan Beulich (cherry picked from commit 6e3f36387de566b09aa4145ea0e3bfe4814d68b4) --- 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 ae076bec3a..c19464da70 100644 --- a/xen/arch/x86/spec_ctrl.c +++ b/xen/arch/x86/spec_ctrl.c @@ -948,13 +948,14 @@ 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. * * In the absence of retpolines, IBRS needs to be used for speculative * safety. All CET-capable hardware has efficient IBRS. */ - if ( cpu_has_xen_shstk ) + if ( read_cr4() & X86_CR4_CET ) { if ( !has_spec_ctrl ) printk(XENLOG_WARNING "?!? CET active, but no MSR_SPEC_CTRL?\n"); -- 2.30.2