x86/speculation/mmio: Enable CPU Fill buffer clearing on idle

commit 99a83db5a605137424e1efe29dc0573d6a5b6316 upstream

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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Co-developed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
CVE-2022-21166
CVE-2022-21123
CVE-2022-21125
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 684c8f88fe51923eb3c11a8d5f006bdb1a5e7e93..7886c2ecb7519f642f2f2b761294a01b0ef9d8ed 100644 (file)
--- 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"