kernel/amd64: Add spectre mitigation support

Add spectre mitigation support for AMD64 hosts which may be enabled via
the --enable-spectre-mitigation configure flag. This commit currently
only adds IBRS support but more techniques may be added later on.

Signed-off-by: sigsegv7 <ian@vegaa.systems>

1 files changed, 78 insertions, 0 deletions

diff --git a/sys/arch/amd64/spectre.c b/sys/arch/amd64/spectre.c
new file mode 100644
index 0000000..00b0237
--- /dev/null
+++ b/sys/arch/amd64/spectre.c
@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2023 Ian Marco Moffett and the VegaOS team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of VegaOS nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <machine/spectre.h>
+#include <machine/cpuid.h>
+#include <machine/msr.h>
+#include <sys/syslog.h>
+#include <sys/types.h>
+
+__MODULE_NAME("spectre");
+__KERNEL_META("$Vega$: spectre.c, Ian Marco Moffett, "
+              "Spectre mitigation support");
+
+#if __SPECTRE_MITIGATION == 1
+
+/*
+ * Returns true if Indirect Branch Restricted Speculation (IBRS)
+ * is supported.
+ */
+__naked bool
+__can_mitigate_spectre(void);
+
+/*
+ * Returns EXIT_FAILURE if not supported, returns
+ * EXIT_SUCCESS if mitigation is now active.
+ *
+ * This function will be NULL if spectre mitigation isn't enabled;
+ * therefore it is wise to verify to prevent access violations and
+ * undefined behaviour.
+ *
+ * This behaviour is governed by the __SPECTRE_MITIGATION define
+ *
+ * TODO: Try to enable others, not just IBRS
+ */
+__weak int
+try_spectre_mitigate(void)
+{
+    uint64_t tmp;
+
+    if (!__can_mitigate_spectre()) {
+        KINFO("IBRS not supported; spectre mitigation NOT enabled\n");
+        return EXIT_FAILURE;
+    }
+
+    KINFO("IBRS supported; spectre mitigation enabled\n");
+    tmp = rdmsr(IA32_SPEC_CTL);
+    tmp |= __BIT(0);                /* IBRS */
+    wrmsr(IA32_SPEC_CTL, tmp);
+    return EXIT_SUCCESS;
+}
+
+#endif      /* __SPECTRE_MITIGATION == 1 */