[RFC PATCH 23/34] x86/bugs: Add attack vector controls for mmio

From: David Kaplan
Date: Thu Sep 12 2024 - 15:13:50 EST


Use attack vectors controls to determine if mmio mitigation is required.

Signed-off-by: David Kaplan <david.kaplan@xxxxxxx>
---
arch/x86/kernel/cpu/bugs.c | 37 ++++++++++++++++++++++---------------
1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index f042c5595463..87ddf0b67d45 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -614,20 +614,26 @@ static void __init mmio_select_mitigation(void)
if (mmio_mitigation == MMIO_MITIGATION_OFF)
return;

- /*
- * Check if the system has the right microcode.
- *
- * CPU Fill buffer clear mitigation is enumerated by either an explicit
- * FB_CLEAR or by the presence of both MD_CLEAR and L1D_FLUSH on MDS
- * affected systems.
- */
- if ((x86_arch_cap_msr & ARCH_CAP_FB_CLEAR) ||
- (boot_cpu_has(X86_FEATURE_MD_CLEAR) &&
- boot_cpu_has(X86_FEATURE_FLUSH_L1D) &&
- !(x86_arch_cap_msr & ARCH_CAP_MDS_NO)))
- mmio_mitigation = MMIO_MITIGATION_VERW;
- else
- mmio_mitigation = MMIO_MITIGATION_UCODE_NEEDED;
+ if (mmio_mitigation == MMIO_MITIGATION_AUTO) {
+ if (should_mitigate_vuln(MMIO)) {
+ /*
+ * Check if the system has the right microcode.
+ *
+ * CPU Fill buffer clear mitigation is enumerated by either an explicit
+ * FB_CLEAR or by the presence of both MD_CLEAR and L1D_FLUSH on MDS
+ * affected systems.
+ */
+ if ((x86_arch_cap_msr & ARCH_CAP_FB_CLEAR) ||
+ (boot_cpu_has(X86_FEATURE_MD_CLEAR) &&
+ boot_cpu_has(X86_FEATURE_FLUSH_L1D) &&
+ !(x86_arch_cap_msr & ARCH_CAP_MDS_NO)))
+ mmio_mitigation = MMIO_MITIGATION_VERW;
+ else
+ mmio_mitigation = MMIO_MITIGATION_UCODE_NEEDED;
+ } else {
+ mmio_mitigation = MMIO_MITIGATION_OFF;
+ }
+ }
}

static void __init mmio_update_mitigation(void)
@@ -675,7 +681,8 @@ static void __init mmio_apply_mitigation(void)
if (!(x86_arch_cap_msr & ARCH_CAP_FBSDP_NO))
static_branch_enable(&mds_idle_clear);

- if (mmio_nosmt || cpu_mitigations_auto_nosmt())
+ if (mmio_nosmt || cpu_mitigations_auto_nosmt() ||
+ cpu_mitigate_attack_vector(CPU_MITIGATE_CROSS_THREAD))
cpu_smt_disable(false);
}

--
2.34.1