[PATCH v4 1/4] xen: add hypercall for reading runtime parameters

[Vasilis Liaskovitis <vliaskovitis@suse.com>]

Add a sysctl hypercall to support reading hypervisor runtime parameters.

Limitations:
- Custom runtime parameters (OPT_CUSTOM) are not supported yet.
- For integer parameters (OPT_UINT), only unsigned parameters are printed
correctly.
- The implementation only reads runtime parameters, but it can be changed
to read all hypervisor parameters if needed. 

Signed-off-by: Vasilis Liaskovitis <vliaskovitis@suse.com>
---
 tools/flask/policy/modules/dom0.te  |   2 +-
 xen/common/kernel.c                 | 118 ++++++++++++++++++++++++++++
 xen/common/sysctl.c                 |  52 +++++++++++-
 xen/include/public/sysctl.h         |  18 +++++
 xen/include/xen/lib.h               |   1 +
 xen/xsm/flask/hooks.c               |   3 +
 xen/xsm/flask/policy/access_vectors |   2 +
 7 files changed, 193 insertions(+), 3 deletions(-)

diff --git a/tools/flask/policy/modules/dom0.te b/tools/flask/policy/modules/dom0.te
index a347d664f8..681d1a101b 100644
--- a/tools/flask/policy/modules/dom0.te
+++ b/tools/flask/policy/modules/dom0.te
@@ -16,7 +16,7 @@ allow dom0_t xen_t:xen {
 allow dom0_t xen_t:xen2 {
 	resource_op psr_cmt_op psr_alloc pmu_ctrl get_symbol
 	get_cpu_levelling_caps get_cpu_featureset livepatch_op
-	coverage_op set_parameter
+	coverage_op set_parameter get_parameter
 };
 
 # Allow dom0 to use all XENVER_ subops that have checks.
diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index 612575430f..6695ffc372 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -12,6 +12,7 @@
 #include <xen/paging.h>
 #include <xen/guest_access.h>
 #include <xen/hypercall.h>
+#include <xen/ctype.h>
 #include <xsm/xsm.h>
 #include <asm/current.h>
 #include <public/version.h>
@@ -52,6 +53,123 @@ static int assign_integer_param(const struct kernel_param *param, uint64_t val)
     return 0;
 }
 
+static int get_integer_param(const struct kernel_param *param, uint64_t *val)
+{
+    switch ( param->len )
+    {
+    case sizeof(uint8_t):
+        *val = *(uint8_t *)param->par.var;
+        break;
+
+    case sizeof(uint16_t):
+        *val = *(uint16_t *)param->par.var;
+        break;
+
+    case sizeof(uint32_t):
+        *val = *(uint32_t *)param->par.var;
+        break;
+
+    case sizeof(uint64_t):
+        *val = *(uint64_t *)param->par.var;
+        break;
+
+    default:
+        BUG();
+        break;
+    }
+
+    return 0;
+}
+
+int runtime_get_params(const char *cmdline, char *values,
+                      size_t maxlen)
+{
+    char opt[128], *optkey, *q, *val = values;
+    const char *p = cmdline;
+    const struct kernel_param *param;
+    int rc = 0, len = 0;
+    size_t bufpos = 0;
+    uint64_t param_int;
+
+    while ( !rc )
+    {
+        /* Skip whitespace. */
+        while ( isspace(*p) )
+            p++;
+        if ( *p == '\0' )
+            break;
+
+        /* Grab the next whitespace-delimited option. */
+        q = optkey = opt;
+        while ( !isspace(*p) && (*p != '\0') )
+        {
+            if ( (q - opt) < (sizeof(opt) - 1) ) /* avoid overflow */
+                *q++ = *p;
+            else return -ENOMEM;
+            p++;
+        }
+        *q = '\0';
+
+        for ( param = __param_start; param < __param_end; param++ )
+        {
+            if ( strcmp(param->name, optkey) )
+                continue;
+
+            switch ( param->type )
+            {
+            case OPT_STR:
+                len = snprintf(val + bufpos, maxlen - bufpos, "%s ",
+                               (char*)param->par.var);
+                break;
+
+            case OPT_UINT:
+            case OPT_SIZE:
+                /* Signed integer parameters are not supported yet.
+                 * While there are no runtime signed integer parameters
+                 * at the moment, adding one and trying to get its value
+                 * with the current implementation will output the wrong
+                 * value.
+                 */
+                get_integer_param(param, &param_int);
+                len = snprintf(val + bufpos, maxlen - bufpos,
+                               "%"PRIu64" ", param_int);
+                break;
+
+            case OPT_BOOL:
+                get_integer_param(param, &param_int);
+                len = snprintf(val + bufpos, maxlen - bufpos, "%s ",
+                               param_int ? "true" : "false");
+                break;
+
+            case OPT_CUSTOM:
+                /* Custom parameters are not supported yet. */
+                rc = -EINVAL;
+                break;
+
+            default:
+                BUG();
+                break;
+            }
+
+            if ( len < 0 )
+                rc = len;
+            else if ( len < maxlen - bufpos )
+                /* if output was not truncated update buffer position. */
+                bufpos += len;
+            else if ( len > 0 )
+                rc = -ENOMEM;
+
+            break;
+        }
+
+        /* no parameter was matched */
+        if ( param >= __param_end )
+            rc = -EINVAL;
+    }
+
+    return rc;
+}
+
 static int parse_params(const char *cmdline, const struct kernel_param *start,
                         const struct kernel_param *end)
 {
diff --git a/xen/common/sysctl.c b/xen/common/sysctl.c
index c0aa6bde4e..20be6a6d8d 100644
--- a/xen/common/sysctl.c
+++ b/xen/common/sysctl.c
@@ -466,9 +466,9 @@ long do_sysctl(XEN_GUEST_HANDLE_PARAM(xen_sysctl_t) u_sysctl)
             copyback = 1;
         break;
 
+#define XEN_PARAMETER_MAX_SIZE 1023
     case XEN_SYSCTL_set_parameter:
     {
-#define XEN_SET_PARAMETER_MAX_SIZE 1023
         char *params;
 
         if ( op->u.set_parameter.pad[0] || op->u.set_parameter.pad[1] ||
@@ -477,7 +477,7 @@ long do_sysctl(XEN_GUEST_HANDLE_PARAM(xen_sysctl_t) u_sysctl)
             ret = -EINVAL;
             break;
         }
-        if ( op->u.set_parameter.size > XEN_SET_PARAMETER_MAX_SIZE )
+        if ( op->u.set_parameter.size > XEN_PARAMETER_MAX_SIZE )
         {
             ret = -E2BIG;
             break;
@@ -501,6 +501,54 @@ long do_sysctl(XEN_GUEST_HANDLE_PARAM(xen_sysctl_t) u_sysctl)
 
         break;
     }
+    case XEN_SYSCTL_get_parameter:
+    {
+        char *params, *values;
+
+        if ( op->u.get_parameter.pad[0] || op->u.get_parameter.pad[1] ||
+             op->u.get_parameter.pad[2] )
+        {
+            ret = -EINVAL;
+            break;
+        }
+        if ( op->u.get_parameter.size > XEN_PARAMETER_MAX_SIZE )
+        {
+            ret = -E2BIG;
+            break;
+        }
+        params = xmalloc_bytes(op->u.get_parameter.size + 1);
+        if ( !params )
+        {
+            ret = -ENOMEM;
+            break;
+        }
+
+        values = xmalloc_bytes(XEN_PARAMETER_MAX_SIZE);
+        if ( !values )
+        {
+            xfree(params);
+            ret = -ENOMEM;
+            break;
+        }
+
+        if ( copy_from_guest(params, op->u.get_parameter.params,
+                             op->u.get_parameter.size) )
+            ret = -EFAULT;
+        else
+        {
+            params[op->u.set_parameter.size] = 0;
+            ret = runtime_get_params(params, values, XEN_PARAMETER_MAX_SIZE);
+
+            if ( !ret && copy_to_guest(op->u.get_parameter.values, values,
+                                       strlen(values)) )
+                ret = -EFAULT;
+        }
+
+        xfree(params);
+        xfree(values);
+
+        break;
+    }
 
     default:
         ret = arch_do_sysctl(op, u_sysctl);
diff --git a/xen/include/public/sysctl.h b/xen/include/public/sysctl.h
index c49b4dcc99..7d77d57115 100644
--- a/xen/include/public/sysctl.h
+++ b/xen/include/public/sysctl.h
@@ -1100,6 +1100,22 @@ typedef struct xen_sysctl_cpu_policy xen_sysctl_cpu_policy_t;
 DEFINE_XEN_GUEST_HANDLE(xen_sysctl_cpu_policy_t);
 #endif
 
+/*
+ * XEN_SYSCTL_get_parameter
+ *
+ * Read hypervisor parameters at runtime.
+ * Parameters are a single string terminated by a NUL byte of max. size
+ * characters. Multiple settings can be specified by separating them
+ * with blanks.
+ */
+
+struct xen_sysctl_get_parameter {
+    XEN_GUEST_HANDLE_64(char) params;       /* IN: pointer to parameters. */
+    XEN_GUEST_HANDLE_64(char) values;       /* OUT: pointer to output values. */
+    uint16_t size;                          /* IN: size of parameters. */
+    uint16_t pad[3];                        /* IN: MUST be zero. */
+};
+
 struct xen_sysctl {
     uint32_t cmd;
 #define XEN_SYSCTL_readconsole                    1
@@ -1130,6 +1146,7 @@ struct xen_sysctl {
 #define XEN_SYSCTL_livepatch_op                  27
 #define XEN_SYSCTL_set_parameter                 28
 #define XEN_SYSCTL_get_cpu_policy                29
+#define XEN_SYSCTL_get_parameter                 30
     uint32_t interface_version; /* XEN_SYSCTL_INTERFACE_VERSION */
     union {
         struct xen_sysctl_readconsole       readconsole;
@@ -1162,6 +1179,7 @@ struct xen_sysctl {
 #if defined(__i386__) || defined(__x86_64__)
         struct xen_sysctl_cpu_policy        cpu_policy;
 #endif
+        struct xen_sysctl_get_parameter     get_parameter;
         uint8_t                             pad[128];
     } u;
 };
diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
index e0b7bcb6b7..6e6367bb7a 100644
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -71,6 +71,7 @@ struct domain;
 void cmdline_parse(const char *cmdline);
 int runtime_parse(const char *line);
 int parse_bool(const char *s, const char *e);
+int runtime_get_params(const char *cmdline, char *values, size_t maxlen);
 
 /**
  * Given a specific name, parses a string of the form:
diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
index 3d00c747f6..1b832e9a4c 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -830,6 +830,9 @@ static int flask_sysctl(int cmd)
     case XEN_SYSCTL_set_parameter:
         return avc_current_has_perm(SECINITSID_XEN, SECCLASS_XEN2,
                                     XEN2__SET_PARAMETER, NULL);
+    case XEN_SYSCTL_get_parameter:
+        return avc_current_has_perm(SECINITSID_XEN, SECCLASS_XEN2,
+                                    XEN2__GET_PARAMETER, NULL);
 
     default:
         return avc_unknown_permission("sysctl", cmd);
diff --git a/xen/xsm/flask/policy/access_vectors b/xen/xsm/flask/policy/access_vectors
index e00448b776..c5ee21d852 100644
--- a/xen/xsm/flask/policy/access_vectors
+++ b/xen/xsm/flask/policy/access_vectors
@@ -103,6 +103,8 @@ class xen2
     coverage_op
 # XEN_SYSCTL_set_parameter
     set_parameter
+# XEN_SYSCTL_get_parameter
+    get_parameter
 }
 
 # Classes domain and domain2 consist of operations that a domain performs on
-- 
2.20.1


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