[Xen-devel] [PATCH V2] xen: support enabling SMEP/SMAP for HVM only

[He Chen <he.chen@xxxxxxxxxxxxxxx>]

Enhance "smep" and "smap" command line options to support enabling SMEP
or SMAP for HVM only with allowing "hvm" as a value.

Signed-off-by: He Chen <he.chen@xxxxxxxxxxxxxxx>
---
Changes in V2:
* Allow "hvm" as a value to "smep" and "smap" command line options.
* Clear SMEP/SMAP CPUID bits for pv guests if they are set to hvm only.
* Refine docs.
* Rewrite commit message.
---
 docs/misc/xen-command-line.markdown | 14 +++++----
 xen/arch/x86/cpuid.c                |  5 ++++
 xen/arch/x86/setup.c                | 58 ++++++++++++++++++++++++++++++++-----
 xen/include/asm-x86/setup.h         |  3 ++
 4 files changed, 66 insertions(+), 14 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index 3a250cb..0e49358 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -1427,19 +1427,21 @@ enabling more sockets and cores to go into deeper sleep 
states.
 
 Set the serial transmit buffer size.
 
-### smep
-> `= <boolean>`
+### smap
+> `= <boolean> | hvm`
 
 > Default: `true`
 
-Flag to enable Supervisor Mode Execution Protection
+Flag to enable Supervisor Mode Access Prevention
+Using `smap=hvm` to enable SMAP for HVM guests only.
 
-### smap
-> `= <boolean>`
+### smep
+> `= <boolean> | hvm`
 
 > Default: `true`
 
-Flag to enable Supervisor Mode Access Prevention
+Flag to enable Supervisor Mode Execution Protection
+Using `smep=hvm` to enable SMEP for HVM guests only.
 
 ### snb\_igd\_quirk
 > `= <boolean> | cap | <integer>`
diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index 38e34bd..afa16b8 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -4,6 +4,7 @@
 #include <asm/hvm/hvm.h>
 #include <asm/hvm/vmx/vmcs.h>
 #include <asm/processor.h>
+#include <asm/setup.h>
 
 const uint32_t known_features[] = INIT_KNOWN_FEATURES;
 const uint32_t special_features[] = INIT_SPECIAL_FEATURES;
@@ -118,6 +119,10 @@ static void __init calculate_pv_featureset(void)
     __set_bit(X86_FEATURE_HTT, pv_featureset);
     __set_bit(X86_FEATURE_X2APIC, pv_featureset);
     __set_bit(X86_FEATURE_CMP_LEGACY, pv_featureset);
+    if ( smep_hvm_only )
+        __clear_bit(X86_FEATURE_SMEP, pv_featureset);
+    if ( smap_hvm_only )
+        __clear_bit(X86_FEATURE_SMAP, pv_featureset);
 
     sanitise_featureset(pv_featureset);
 }
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 217c775..625b9b4 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -61,13 +61,19 @@ boolean_param("nosmp", opt_nosmp);
 static unsigned int __initdata max_cpus;
 integer_param("maxcpus", max_cpus);
 
-/* smep: Enable/disable Supervisor Mode Execution Protection (default on). */
-static bool_t __initdata opt_smep = 1;
-boolean_param("smep", opt_smep);
-
-/* smap: Enable/disable Supervisor Mode Access Prevention (default on). */
-static bool_t __initdata opt_smap = 1;
-boolean_param("smap", opt_smap);
+/* Supervisor Mode Execution Protection (default on). */
+/* "smep=on": Enable SMEP for Xen and guests.         */
+/* "smep=hvm": Enable SMEP for HVM only.              */
+/* "smep=off": Disable SMEP for Xen and guests.       */
+static void parse_smep_param(char *s);
+custom_param("smep", parse_smep_param);
+
+/* Supervisor Mode Access Prevention (default on). */
+/* "smep=on": Enable SMAP for Xen and guests.      */
+/* "smep=hvm": Enable SMAP for HVM only.           */
+/* "smep=off": Disable SMAP for Xen and guests.    */
+static void parse_smap_param(char *s);
+custom_param("smap", parse_smap_param);
 
 unsigned long __read_mostly cr4_pv32_mask;
 
@@ -111,6 +117,34 @@ struct cpuinfo_x86 __read_mostly boot_cpu_data = { 0, 0, 
0, 0, -1 };
 
 unsigned long __read_mostly mmu_cr4_features = XEN_MINIMAL_CR4;
 
+static bool_t __initdata opt_smep = 1;
+bool_t __initdata smep_hvm_only = 0;
+static void __init parse_smep_param(char *s)
+{
+    if ( !parse_bool(s) )
+    {
+        opt_smep = 0;
+    }
+    else if ( !strcmp(s, "hvm") )
+    {
+        smep_hvm_only = 1;
+    }
+}
+
+static bool_t __initdata opt_smap = 1;
+bool_t __initdata smap_hvm_only = 0;
+static void __init parse_smap_param(char *s)
+{
+    if ( !parse_bool(s) )
+    {
+        opt_smap = 0;
+    }
+    else if ( !strcmp(s, "hvm") )
+    {
+        smap_hvm_only = 1;
+    }
+}
+
 bool_t __read_mostly acpi_disabled;
 bool_t __initdata acpi_force;
 static char __initdata acpi_param[10] = "";
@@ -1404,12 +1438,20 @@ void __init noreturn __start_xen(unsigned long mbi_p)
     if ( !opt_smep )
         setup_clear_cpu_cap(X86_FEATURE_SMEP);
     if ( cpu_has_smep )
+    {
         set_in_cr4(X86_CR4_SMEP);
+        if ( smep_hvm_only )
+            write_cr4(read_cr4() & ~X86_CR4_SMEP);
+    }
 
     if ( !opt_smap )
         setup_clear_cpu_cap(X86_FEATURE_SMAP);
     if ( cpu_has_smap )
+    {
         set_in_cr4(X86_CR4_SMAP);
+        if ( smap_hvm_only )
+            write_cr4(read_cr4() & ~X86_CR4_SMAP);
+    }
 
     cr4_pv32_mask = mmu_cr4_features & XEN_CR4_PV32_BITS;
 
@@ -1570,7 +1612,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
                         bootstrap_map, cmdline) != 0)
         panic("Could not set up DOM0 guest OS");
 
-    if ( cpu_has_smap )
+    if ( cpu_has_smap && !smap_hvm_only )
     {
         write_cr4(read_cr4() | X86_CR4_SMAP);
         cr4_pv32_mask |= X86_CR4_SMAP;
diff --git a/xen/include/asm-x86/setup.h b/xen/include/asm-x86/setup.h
index c65b79c..a0e69ae 100644
--- a/xen/include/asm-x86/setup.h
+++ b/xen/include/asm-x86/setup.h
@@ -51,6 +51,9 @@ void microcode_grab_module(
 
 extern uint8_t kbd_shift_flags;
 
+extern bool_t smep_hvm_only;
+extern bool_t smap_hvm_only;
+
 #ifdef NDEBUG
 # define highmem_start 0
 #else
-- 
1.9.1


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