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>

6 files changed, 194 insertions, 1 deletions

diff --git a/Makefile.in b/Makefile.in
index 7f1fa5e..63a0a35 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -1,5 +1,18 @@
 .SILENT:
 
+
+###############################
+# Feature stuff
+###############################
+override SPECTRE_MITIGATION = @SPECTRE_MITIGATION@
+
+ifeq ($(SPECTRE_MITIGATION), 1)
+	override SPECTRE_FLAGS=-D__SPECTRE_MITIGATION
+else
+	override SPECTRE_FLAGS=
+endif
+
+
 ###############################
 # CFLAGS, QEMU flags + misc
 ###############################
@@ -9,7 +22,8 @@ override PROMPT := printf "%s\t\t%s\n"
 override KERNEL_DEFINES =  -DVEGA_VERSION="\"$(VEGA_VERSION)\""\
 			   -DVEGA_BUILDDATE="\"@VEGA_BUILDDATE@\""\
 			   -DVEGA_BUILDBRANCH="\"@VEGA_BUILDBRANCH@\""\
-			   -DVEGA_ARCH="\"@ARCH@\""
+			   -DVEGA_ARCH="\"@ARCH@\""\
+			   $(SPECTRE_FLAGS)
 override KERNEL_CFLAGS = @KERNEL_CFLAGS@ $(KERNEL_DEFINES)
 override KERNEL_LDFLAGS = -nostdlib -zmax-page-size=0x1000 -static -Tconf/link-$(ARCH).ld
 override QEMU_FLAGS = @QEMU_FLAGS@
diff --git a/configure.ac b/configure.ac
index 5d2d9a0..253b69d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -16,6 +16,18 @@ QEMU_FLAGS_X86_64="--enable-kvm -monitor stdio 	\\
 VEGA_BUILDDATE=`export LANG=en_US.UTF-8 ; date`
 VEGA_BUILDBRANCH="`basename $PWD`"
 
+# Enable Spectre mitigation option
+AC_ARG_ENABLE([spectre-mitigation],
+    [AS_HELP_STRING([--enable-spectre-mitigation], [Enable Spectre mitigation (IBRS or similar)])],,
+    [enable_spectre_mitigation=$enableval])
+
+
+if test "x$enable_spectre_mitigation" = "xyes"; then
+    AC_SUBST(SPECTRE_MITIGATION, [1])
+else
+    AC_SUBST(SPECTRE_MITIGATION, [0])
+fi
+
 AC_SUBST(VEGA_BUILDDATE, [$VEGA_BUILDDATE])
 AC_SUBST(VEGA_BUILDBRANCH, [$VEGA_BUILDBRANCH])
 
diff --git a/sys/arch/amd64/spectre.S b/sys/arch/amd64/spectre.S
new file mode 100644
index 0000000..f91f744
--- /dev/null
+++ b/sys/arch/amd64/spectre.S
@@ -0,0 +1,49 @@
+/*
+ * 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.
+ */
+
+.text
+.globl __can_mitigate_spectre
+
+__can_mitigate_spectre:
+    xor %ecx, %ecx          // NULL out ECX
+    mov $0x7, %eax          // 0x7 (Check IBRS)
+    cpuid
+
+    /* Check if supported (if EDX[26] == 1) */
+    mov $1, %ebx
+    shl $26, %ebx
+    test %ebx, %edx
+    jnz supported
+not_supported:
+    xor %rax, %rax
+    jmp 1f
+supported:
+    mov $1, %rax
+1:
+    ret
diff --git a/sys/arch/amd64/spectre.c b/sys/arch/amd64/spectre.c
new file mode 100644
index 0000000..00b0237
--- /dev/null
+++ b/sys/arch/amd64/spectre.c
@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2023 Ian Marco Moffett and the VegaOS team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of VegaOS nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <machine/spectre.h>
+#include <machine/cpuid.h>
+#include <machine/msr.h>
+#include <sys/syslog.h>
+#include <sys/types.h>
+
+__MODULE_NAME("spectre");
+__KERNEL_META("$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 */
diff --git a/sys/include/arch/amd64/msr.h b/sys/include/arch/amd64/msr.h
index 9d3a8bf..ebd2776 100644
--- a/sys/include/arch/amd64/msr.h
+++ b/sys/include/arch/amd64/msr.h
@@ -33,6 +33,8 @@
 #include <sys/types.h>
 #include <sys/cdefs.h>
 
+#define IA32_SPEC_CTL   0x00000048
+
 static inline uint64_t
 rdmsr(uint32_t msr_addr)
 {
diff --git a/sys/include/arch/amd64/spectre.h b/sys/include/arch/amd64/spectre.h
new file mode 100644
index 0000000..a4c01fb
--- /dev/null
+++ b/sys/include/arch/amd64/spectre.h
@@ -0,0 +1,38 @@
+/*
+ * 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.
+ */
+
+#ifndef _AMD64_SPECTRE_H_
+#define _AMD64_SPECTRE_H_
+
+#include <sys/cdefs.h>
+#include <sys/errno.h>
+
+__weak int try_spectre_mitigate(void);
+
+#endif