From d37a8a067e62e3b6709d224c22f740fdda9d0078 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Mon, 1 Nov 2021 21:54:26 +0000 Subject: [PATCH] x86/EFI: Disable CET-IBT around Runtime Services calls UEFI Runtime services, at the time of writing, aren't CET-IBT compatible. Work is ongoing to address this. In the meantime, unconditionally disable IBT. Signed-off-by: Andrew Cooper Reviewed-by: Jan Beulich --- xen/common/efi/runtime.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/xen/common/efi/runtime.c b/xen/common/efi/runtime.c index e3ce85d118..13b0975866 100644 --- a/xen/common/efi/runtime.c +++ b/xen/common/efi/runtime.c @@ -21,6 +21,7 @@ struct efi_rs_state { * don't strictly need that. */ unsigned long __aligned(32) cr3; + unsigned long msr_s_cet; #endif }; @@ -113,6 +114,19 @@ struct efi_rs_state efi_rs_enter(void) switch_cr3_cr4(mfn_to_maddr(efi_l4_mfn), read_cr4()); + /* + * At the time of writing (2022), no UEFI firwmare is CET-IBT compatible. + * Work is under way to remedy this. + * + * Stash MSR_S_CET and clobber ENDBR_EN. This is necessary because + * SHSTK_EN isn't configured until very late on the BSP. + */ + if ( cpu_has_xen_ibt ) + { + rdmsrl(MSR_S_CET, state.msr_s_cet); + wrmsrl(MSR_S_CET, state.msr_s_cet & ~CET_ENDBR_EN); + } + return state; } @@ -122,6 +136,10 @@ void efi_rs_leave(struct efi_rs_state *state) if ( !state->cr3 ) return; + + if ( state->msr_s_cet ) + wrmsrl(MSR_S_CET, state->msr_s_cet); + switch_cr3_cr4(state->cr3, read_cr4()); if ( is_pv_vcpu(curr) && !is_idle_vcpu(curr) ) { -- 2.30.2