kernel: support for Intel SMAP and SMEP on x86_64.

SMAP will generated page faults when the kernel tries to access user pages unless overriden.
If SMAP is enabled, the override instructions are written where needed in memory with
binary "altcodepatches".
Support is enabled by default, might be disabled per safemode setting.

Change-Id: Ife26cd765056aeaf65b2ffa3cadd0dcf4e273a96

headers/private/kernel/arch/generic/user_memory.h

@@ -1,4 +1,5 @@
 /*
+ * Copyright 2018, Jérôme Duval, [email protected].
  * Copyright 2014, Paweł Dziepak, [email protected].
  * Distributed under the terms of the MIT License.
  */
@@ -50,7 +51,9 @@ bool user_access(Function function)
 	// destructor.
 	auto fail = setjmp(thread_get_current_thread()->fault_handler_state);
 	if (fail == 0) {
+		set_ac();
 		function();
+		clear_ac();
 		return true;
 	}
 	return false;

headers/private/kernel/arch/x86/arch_altcodepatch.h

@@ -20,6 +20,10 @@
 #define ASM_NOP9	.byte 0x66, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00
 
 
+#define ALTCODEPATCH_TAG_STAC		1
+#define ALTCODEPATCH_TAG_CLAC		2
+
+
 #ifdef _ASSEMBLER
 
 #define CODEPATCH_START	990:
@@ -30,6 +34,14 @@
 	.short			tag				;	\
 	.popsection
 
+#define ASM_STAC	CODEPATCH_START \
+					ASM_NOP3	;	 \
+					CODEPATCH_END(ALTCODEPATCH_TAG_STAC)
+
+#define ASM_CLAC	CODEPATCH_START \
+					ASM_NOP3	;	\
+					CODEPATCH_END(ALTCODEPATCH_TAG_CLAC)
+
 #else
 
 #define _STRINGIFY(x...)	#x
@@ -43,6 +55,15 @@
 	".short			" STRINGIFY(tag)	"	\n" \
 	".popsection"
 
+#define ASM_STAC	CODEPATCH_START \
+					STRINGIFY(ASM_NOP3)	"\n" \
+					CODEPATCH_END(ALTCODEPATCH_TAG_STAC)
+
+#define ASM_CLAC	CODEPATCH_START \
+					STRINGIFY(ASM_NOP3)	"\n"\
+					CODEPATCH_END(ALTCODEPATCH_TAG_CLAC)
+
+
 void arch_altcodepatch_replace(uint16 tag, void* newcodepatch, size_t length);
 
 

headers/private/kernel/arch/x86/arch_cpu.h

@@ -17,6 +17,7 @@
 
 #include <arch_thread_types.h>
 
+#include <arch/x86/arch_altcodepatch.h>
 #include <arch/x86/descriptors.h>
 
 #ifdef __x86_64__
@@ -272,10 +273,6 @@
 #define IA32_FEATURE_AMD_EXT_IBPB	(1 << 12)	/* IBPB Support only (no IBRS) */
 
 
-// cr4 flags
-#define IA32_CR4_PAE					(1UL << 5)
-#define IA32_CR4_GLOBAL_PAGES			(1UL << 7)
-
 // Memory type ranges
 #define IA32_MTR_UNCACHED				0
 #define IA32_MTR_WRITE_COMBINING		1
@@ -299,7 +296,7 @@
 #define X86_EFLAGS_NESTED_TASK					0x00004000
 #define X86_EFLAGS_RESUME						0x00010000
 #define X86_EFLAGS_V86_MODE						0x00020000
-#define X86_EFLAGS_ALIGNMENT_CHECK				0x00040000
+#define X86_EFLAGS_ALIGNMENT_CHECK				0x00040000	// also SMAP status
 #define X86_EFLAGS_VIRTUAL_INTERRUPT			0x00080000
 #define X86_EFLAGS_VIRTUAL_INTERRUPT_PENDING	0x00100000
 #define X86_EFLAGS_ID							0x00200000
@@ -313,9 +310,20 @@
 #define CR0_FPU_EMULATION		(1UL << 2)
 #define CR0_MONITOR_FPU			(1UL << 1)
 
+// cr4 flags
+#define IA32_CR4_PAE			(1UL << 5)
+#define IA32_CR4_GLOBAL_PAGES	(1UL << 7)
 #define CR4_OS_FXSR				(1UL << 9)
 #define CR4_OS_XMM_EXCEPTION	(1UL << 10)
+#define IA32_CR4_SMEP			(1UL << 20)
+#define IA32_CR4_SMAP			(1UL << 21)
 
+// page fault error codes (http://wiki.osdev.org/Page_Fault)
+#define PGFAULT_P						0x01	// Protection violation
+#define PGFAULT_W						0x02	// Write
+#define PGFAULT_U						0x04	// Usermode
+#define PGFAULT_RSVD					0x08	// Reserved bits
+#define PGFAULT_I						0x10	// Instruction fetch
 
 // iframe types
 #define IFRAME_TYPE_SYSCALL				0x1
@@ -461,6 +469,12 @@ typedef struct arch_cpu_info {
 #define wbinvd() \
 	__asm__("wbinvd")
 
+#define set_ac() \
+	__asm__ volatile (ASM_STAC : : : "memory")
+
+#define clear_ac() \
+	__asm__ volatile (ASM_CLAC : : : "memory")
+
 #define out8(value,port) \
 	__asm__ ("outb %%al,%%dx" : : "a" (value), "d" (port))
 

headers/private/system/safemode_defs.h

@@ -12,6 +12,7 @@
 #define B_SAFEMODE_DISABLE_ACPI				"disable_acpi"
 #define B_SAFEMODE_DISABLE_APIC				"disable_apic"
 #define B_SAFEMODE_ENABLE_X2APIC			"enable_x2apic"
+#define B_SAFEMODE_DISABLE_SMEP_SMAP		"disable_smep_smap"
 #define B_SAFEMODE_DISABLE_APM				"disable_apm"
 #define B_SAFEMODE_DISABLE_SMP				"disable_smp"
 #define B_SAFEMODE_DISABLE_HYPER_THREADING	"disable_hyperthreading"