From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Date: Thu, 19 May 2022 20:31:12 -0700
Subject: x86/speculation/mmio: Enable CPU Fill buffer clearing on idle
Git-commit: 99a83db5a605137424e1efe29dc0573d6a5b6316
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
Patch-mainline: Queued in tip for v5.19
References: bsc#1199650 CVE-2022-21166 CVE-2022-21127 CVE-2022-21123 CVE-2022-21125 CVE-2022-21180

When the CPU is affected by Processor MMIO Stale Data vulnerabilities,
Fill Buffer Stale Data Propagator (FBSDP) can propagate stale data out
of Fill buffer to uncore buffer when CPU goes idle. Stale data can then
be exploited with other variants using MMIO operations.

Mitigate it by clearing the Fill buffer before entering idle state.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Co-developed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/kernel/cpu/bugs.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index d2cc7dbba5e2..56d5dea5e128 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -433,6 +433,14 @@ static void __init mmio_select_mitigation(void)
 	else
 		static_branch_enable(&mmio_stale_data_clear);
 
+	/*
+	 * If Processor-MMIO-Stale-Data bug is present and Fill Buffer data can
+	 * be propagated to uncore buffers, clearing the Fill buffers on idle
+	 * is required irrespective of SMT state.
+	 */
+	if (!(ia32_cap & ARCH_CAP_FBSDP_NO))
+		static_branch_enable(&mds_idle_clear);
+
 	/*
 	 * Check if the system has the right microcode.
 	 *
@@ -1225,6 +1233,8 @@ static void update_indir_branch_cond(void)
 /* Update the static key controlling the MDS CPU buffer clear in idle */
 static void update_mds_branch_idle(void)
 {
+	u64 ia32_cap = x86_read_arch_cap_msr();
+
 	/*
 	 * Enable the idle clearing if SMT is active on CPUs which are
 	 * affected only by MSBDS and not any other MDS variant.
@@ -1236,10 +1246,12 @@ static void update_mds_branch_idle(void)
 	if (!boot_cpu_has_bug(X86_BUG_MSBDS_ONLY))
 		return;
 
-	if (sched_smt_active())
+	if (sched_smt_active()) {
 		static_branch_enable(&mds_idle_clear);
-	else
+	} else if (mmio_mitigation == MMIO_MITIGATION_OFF ||
+		   (ia32_cap & ARCH_CAP_FBSDP_NO)) {
 		static_branch_disable(&mds_idle_clear);
+	}
 }
 
 #define MDS_MSG_SMT "MDS CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html for more details.\n"