[PATCH v3 2/4] xen/x86: introduce self modifying code test

[Roger Pau Monne <roger.pau@citrix.com>]

Introduce a helper to perform checks related to self modifying code, and start
by creating a simple test to check that alternatives have been applied.

Such test is hooked into the boot process and called just after alternatives
have been applied.  In case of failure a message is printed, and the hypervisor
is tainted as not having passed the tests, this does require introducing a new
taint bit (printed as 'A').

A new sysctl is also introduced to run the tests on demand.  While there are no
current users introduced here, further changes will introduce those, and it's
helpful to have the interface defined in the sysctl header from the start.

Note the sysctl visibility is not limited to x86, albeit the only
implementation is for x86.  It's expected that other architectures can reuse
the same sysctl and structure, with possibly different tests.  Leave adjusting
those to when support for a different architecture is introduced, as the
sysctl interface is not stable anyway.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Changes since v2:
 - Rename to smoc and place in test/smoc*
 - fix inline assembly.

Changes since v1:
 - Rework test and interface.
---
 tools/include/xenctrl.h              |  2 +
 tools/libs/ctrl/xc_misc.c            | 14 ++++++
 xen/arch/x86/Makefile                |  1 +
 xen/arch/x86/include/asm/test-smoc.h | 18 ++++++++
 xen/arch/x86/setup.c                 |  3 ++
 xen/arch/x86/sysctl.c                |  9 ++++
 xen/arch/x86/test/Makefile           |  1 +
 xen/arch/x86/test/smoc.c             | 68 ++++++++++++++++++++++++++++
 xen/common/kernel.c                  |  5 +-
 xen/include/public/sysctl.h          | 10 ++++
 xen/include/xen/lib.h                |  1 +
 11 files changed, 130 insertions(+), 2 deletions(-)
 create mode 100644 xen/arch/x86/include/asm/test-smoc.h
 create mode 100644 xen/arch/x86/test/Makefile
 create mode 100644 xen/arch/x86/test/smoc.c

diff --git a/tools/include/xenctrl.h b/tools/include/xenctrl.h
index 2ef8b4e05422..0af796ae84e8 100644
--- a/tools/include/xenctrl.h
+++ b/tools/include/xenctrl.h
@@ -2658,6 +2658,8 @@ int xc_dt_overlay(xc_interface *xch, void *overlay_fdt,
                   uint32_t overlay_fdt_size, uint8_t overlay_op);
 #endif
 
+int xc_test_smoc(xc_interface *xch, uint32_t tests, uint32_t *result);
+
 /* Compat shims */
 #include "xenctrl_compat.h"
 
diff --git a/tools/libs/ctrl/xc_misc.c b/tools/libs/ctrl/xc_misc.c
index 5ecdfa2c7934..1d3d5929cf96 100644
--- a/tools/libs/ctrl/xc_misc.c
+++ b/tools/libs/ctrl/xc_misc.c
@@ -1021,6 +1021,20 @@ int xc_livepatch_replace(xc_interface *xch, char *name, uint32_t timeout, uint32
     return _xc_livepatch_action(xch, name, LIVEPATCH_ACTION_REPLACE, timeout, flags);
 }
 
+int xc_test_smoc(xc_interface *xch, uint32_t tests, uint32_t *result)
+{
+    struct xen_sysctl sysctl = {
+        .cmd = XEN_SYSCTL_test_smoc,
+        .u.test_smoc.tests = tests,
+    };
+    int rc = do_sysctl(xch, &sysctl);
+
+    if ( !rc )
+        *result = sysctl.u.test_smoc.results;
+
+    return rc;
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index f3abdf9cd111..ad5112b03c64 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -8,6 +8,7 @@ obj-$(CONFIG_HVM) += hvm/
 obj-y += mm/
 obj-$(CONFIG_XENOPROF) += oprofile/
 obj-$(CONFIG_PV) += pv/
+obj-y += test/
 obj-y += x86_64/
 obj-y += x86_emulate/
 
diff --git a/xen/arch/x86/include/asm/test-smoc.h b/xen/arch/x86/include/asm/test-smoc.h
new file mode 100644
index 000000000000..2547b925d291
--- /dev/null
+++ b/xen/arch/x86/include/asm/test-smoc.h
@@ -0,0 +1,18 @@
+#ifndef _ASM_X86_TEST_SMC_H_
+#define _ASM_X86_TEST_SMC_H_
+
+#include <xen/types.h>
+
+int test_smoc(uint32_t selection, uint32_t *results);
+
+#endif	/* _ASM_X86_TEST_SMC_H_ */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 3cba2be0af6c..e026b0ea5adc 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -58,6 +58,7 @@
 #include <asm/microcode.h>
 #include <asm/prot-key.h>
 #include <asm/pv/domain.h>
+#include <asm/test-smoc.h>
 
 /* opt_nosmp: If true, secondary processors are ignored. */
 static bool __initdata opt_nosmp;
@@ -1951,6 +1952,8 @@ void asmlinkage __init noreturn __start_xen(unsigned long mbi_p)
 
     alternative_branches();
 
+    test_smoc(XEN_SYSCTL_TEST_SMOC_ALL, NULL);
+
     /*
      * NB: when running as a PV shim VCPUOP_up/down is wired to the shim
      * physical cpu_add/remove functions, so launch the guest with only
diff --git a/xen/arch/x86/sysctl.c b/xen/arch/x86/sysctl.c
index 1d40d82c5ad2..918e56631b94 100644
--- a/xen/arch/x86/sysctl.c
+++ b/xen/arch/x86/sysctl.c
@@ -25,6 +25,7 @@
 #include <asm/processor.h>
 #include <asm/setup.h>
 #include <asm/smp.h>
+#include <asm/test-smoc.h>
 #include <asm/numa.h>
 #include <xen/nodemask.h>
 #include <xen/cpu.h>
@@ -423,6 +424,14 @@ long arch_do_sysctl(
         break;
     }
 
+    case XEN_SYSCTL_test_smoc:
+        ret = test_smoc(sysctl->u.test_smoc.tests,
+                        &sysctl->u.test_smoc.results);
+        if ( !ret && __copy_field_to_guest(u_sysctl, sysctl,
+                                           u.test_smoc.results) )
+            ret = -EFAULT;
+        break;
+
     default:
         ret = -ENOSYS;
         break;
diff --git a/xen/arch/x86/test/Makefile b/xen/arch/x86/test/Makefile
new file mode 100644
index 000000000000..b504b8196659
--- /dev/null
+++ b/xen/arch/x86/test/Makefile
@@ -0,0 +1 @@
+obj-y += smoc.o
diff --git a/xen/arch/x86/test/smoc.c b/xen/arch/x86/test/smoc.c
new file mode 100644
index 000000000000..e7529f937a5a
--- /dev/null
+++ b/xen/arch/x86/test/smoc.c
@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <xen/errno.h>
+
+#include <asm/alternative.h>
+#include <asm/cpufeature.h>
+#include <asm/test-smoc.h>
+
+static bool cf_check test_insn_replacement(void)
+{
+#define EXPECTED_VALUE 2
+    unsigned int r = ~EXPECTED_VALUE;
+
+    alternative_io("", "mov %1, %0", X86_FEATURE_ALWAYS,
+                   "+r" (r), "i" (EXPECTED_VALUE));
+
+    return r == EXPECTED_VALUE;
+#undef EXPECTED_VALUE
+}
+
+int test_smoc(uint32_t selection, uint32_t *results)
+{
+    struct {
+        unsigned int mask;
+        bool (*test)(void);
+        const char *name;
+    } static const tests[] = {
+        { XEN_SYSCTL_TEST_SMOC_INSN_REPL, &test_insn_replacement,
+          "alternative instruction replacement" },
+    };
+    unsigned int i;
+
+    if ( selection & ~XEN_SYSCTL_TEST_SMOC_ALL )
+        return -EINVAL;
+
+    if ( results )
+        *results = 0;
+
+    printk(XENLOG_INFO "Checking Self Modify Code\n");
+
+    for ( i = 0; i < ARRAY_SIZE(tests); i++ )
+    {
+        if ( !(selection & tests[i].mask) )
+            continue;
+
+        if ( tests[i].test() )
+        {
+            if ( results )
+                *results |= tests[i].mask;
+            continue;
+        }
+
+        add_taint(TAINT_ERROR_SMOC);
+        printk(XENLOG_ERR "%s test failed\n", tests[i].name);
+    }
+
+    return 0;
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index 08dbaa2a054c..8ddfd309f65e 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -386,13 +386,14 @@ char *print_tainted(char *str)
 {
     if ( tainted )
     {
-        snprintf(str, TAINT_STRING_MAX_LEN, "Tainted: %c%c%c%c%c%c",
+        snprintf(str, TAINT_STRING_MAX_LEN, "Tainted: %c%c%c%c%c%c%c",
                  tainted & TAINT_MACHINE_INSECURE ? 'I' : ' ',
                  tainted & TAINT_MACHINE_CHECK ? 'M' : ' ',
                  tainted & TAINT_SYNC_CONSOLE ? 'C' : ' ',
                  tainted & TAINT_ERROR_INJECT ? 'E' : ' ',
                  tainted & TAINT_HVM_FEP ? 'H' : ' ',
-                 tainted & TAINT_CPU_OUT_OF_SPEC ? 'S' : ' ');
+                 tainted & TAINT_CPU_OUT_OF_SPEC ? 'S' : ' ',
+                 tainted & TAINT_ERROR_SMOC ? 'A' : ' ');
     }
     else
     {
diff --git a/xen/include/public/sysctl.h b/xen/include/public/sysctl.h
index 9b19679caeb1..4b17f1344732 100644
--- a/xen/include/public/sysctl.h
+++ b/xen/include/public/sysctl.h
@@ -1180,6 +1180,7 @@ struct xen_sysctl_cpu_policy {
 };
 typedef struct xen_sysctl_cpu_policy xen_sysctl_cpu_policy_t;
 DEFINE_XEN_GUEST_HANDLE(xen_sysctl_cpu_policy_t);
+
 #endif
 
 #if defined(__arm__) || defined (__aarch64__)
@@ -1201,6 +1202,13 @@ struct xen_sysctl_dt_overlay {
 };
 #endif
 
+struct xen_sysctl_test_smoc {
+    uint32_t tests;     /* IN: bitmap with selected tests to execute. */
+#define XEN_SYSCTL_TEST_SMOC_INSN_REPL   (1U << 0)
+#define XEN_SYSCTL_TEST_SMOC_ALL         (XEN_SYSCTL_TEST_SMOC_INSN_REPL)
+    uint32_t results;   /* OUT: test result: 1 -> success, 0 -> failure. */
+};
+
 struct xen_sysctl {
     uint32_t cmd;
 #define XEN_SYSCTL_readconsole                    1
@@ -1232,6 +1240,7 @@ struct xen_sysctl {
 /* #define XEN_SYSCTL_set_parameter              28 */
 #define XEN_SYSCTL_get_cpu_policy                29
 #define XEN_SYSCTL_dt_overlay                    30
+#define XEN_SYSCTL_test_smoc                     31
     uint32_t interface_version; /* XEN_SYSCTL_INTERFACE_VERSION */
     union {
         struct xen_sysctl_readconsole       readconsole;
@@ -1259,6 +1268,7 @@ struct xen_sysctl {
         struct xen_sysctl_cpu_levelling_caps cpu_levelling_caps;
         struct xen_sysctl_cpu_featureset    cpu_featureset;
         struct xen_sysctl_livepatch_op      livepatch;
+        struct xen_sysctl_test_smoc         test_smoc;
 #if defined(__i386__) || defined(__x86_64__)
         struct xen_sysctl_cpu_policy        cpu_policy;
 #endif
diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
index 1793be5b6b89..575431e4bd38 100644
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -167,6 +167,7 @@ uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c);
 #define TAINT_HVM_FEP                   (1u << 3)
 #define TAINT_MACHINE_INSECURE          (1u << 4)
 #define TAINT_CPU_OUT_OF_SPEC           (1u << 5)
+#define TAINT_ERROR_SMOC                (1U << 6)
 extern unsigned int tainted;
 #define TAINT_STRING_MAX_LEN            20
 extern char *print_tainted(char *str);
-- 
2.43.0