Add support for dynamic mitigation for CVE-2018-3639

Some CPUS may benefit from using a dynamic mitigation approach for
CVE-2018-3639.  A new SMC interface is defined to allow software
executing in lower ELs to enable or disable the mitigation for their
execution context.

It should be noted that regardless of the state of the mitigation for
lower ELs, code executing in EL3 is always mitigated against
CVE-2018-3639.

NOTE: This change is a compatibility break for any platform using
the declare_cpu_ops_workaround_cve_2017_5715 macro.  Migrate to
the declare_cpu_ops_wa macro instead.

Change-Id: I3509a9337ad217bbd96de9f380c4ff8bf7917013
Signed-off-by: Dimitris Papastamos <dimitris.papastamos@arm.com>

docs/cpu-specific-build-macros.rst

@@ -30,6 +30,11 @@ vulnerability workarounds should be applied at runtime.
    CVE-2018-3639, in order to comply with the recommendation in the spec
    regarding workaround discovery.
 
+-  ``DYNAMIC_WORKAROUND_CVE_2018_3639``: Enables dynamic mitigation for
+   `CVE-2018-3639`_. This build option should be set to 1 if the target
+   platform contains at least 1 CPU that requires dynamic mitigation.
+   Defaults to 0.
+
 CPU Errata Workarounds
 ----------------------
 

include/lib/cpus/aarch64/cpu_macros.S

@@ -18,6 +18,9 @@
 /* Special constant to specify that CPU has no reset function */
 #define CPU_NO_RESET_FUNC		0
 
+#define CPU_NO_EXTRA1_FUNC		0
+#define CPU_NO_EXTRA2_FUNC		0
+
 /* Word size for 64-bit CPUs */
 #define CPU_WORD_SIZE			8
 
@@ -48,6 +51,8 @@ CPU_RESET_FUNC: /* cpu_ops reset_func */
 #endif
 CPU_EXTRA1_FUNC:
 	.space	8
+CPU_EXTRA2_FUNC:
+	.space	8
 #ifdef IMAGE_BL31 /* The power down core and cluster is needed only in BL31 */
 CPU_PWR_DWN_OPS: /* cpu_ops power down functions */
 	.space  (8 * CPU_MAX_PWR_DWN_OPS)
@@ -119,6 +124,10 @@ CPU_OPS_SIZE = .
 	 *	This is a placeholder for future per CPU operations.  Currently,
 	 *	some CPUs use this entry to set a test function to determine if
 	 *	the workaround for CVE-2017-5715 needs to be applied or not.
+	 * _extra2:
+	 *	This is a placeholder for future per CPU operations.  Currently
+	 *	some CPUs use this entry to set a function to disable the
+	 *	workaround for CVE-2018-3639.
 	 * _power_down_ops:
 	 *	Comma-separated list of functions to perform power-down
 	 *	operatios on the CPU. At least one, and up to
@@ -129,7 +138,7 @@ CPU_OPS_SIZE = .
 	 *	used to handle power down at subsequent levels
 	 */
 	.macro declare_cpu_ops_base _name:req, _midr:req, _resetfunc:req, \
-		_extra1:req, _power_down_ops:vararg
+		_extra1:req, _extra2:req, _power_down_ops:vararg
 	.section cpu_ops, "a"
 	.align 3
 	.type cpu_ops_\_name, %object
@@ -138,6 +147,7 @@ CPU_OPS_SIZE = .
 	.quad \_resetfunc
 #endif
 	.quad \_extra1
+	.quad \_extra2
 #ifdef IMAGE_BL31
 1:
 	/* Insert list of functions */
@@ -196,14 +206,15 @@ CPU_OPS_SIZE = .
 
 	.macro declare_cpu_ops _name:req, _midr:req, _resetfunc:req, \
 		_power_down_ops:vararg
-		declare_cpu_ops_base \_name, \_midr, \_resetfunc, 0, \
+		declare_cpu_ops_base \_name, \_midr, \_resetfunc, 0, 0, \
 			\_power_down_ops
 	.endm
 
-	.macro declare_cpu_ops_workaround_cve_2017_5715 _name:req, _midr:req, \
-		_resetfunc:req, _extra1:req, _power_down_ops:vararg
+	.macro declare_cpu_ops_wa _name:req, _midr:req, \
+		_resetfunc:req, _extra1:req, _extra2:req, \
+		_power_down_ops:vararg
 		declare_cpu_ops_base \_name, \_midr, \_resetfunc, \
-			\_extra1, \_power_down_ops
+			\_extra1, \_extra2, \_power_down_ops
 	.endm
 
 #if REPORT_ERRATA

include/lib/cpus/wa_cve_2018_3639.h

@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef __WA_CVE_2018_3639_H__
+#define __WA_CVE_2018_3639_H__
+
+void *wa_cve_2018_3639_get_disable_ptr(void);
+
+#endif /* __WA_CVE_2018_3639_H__ */

include/lib/el3_runtime/aarch64/context.h

@@ -128,8 +128,8 @@
  * Constants that allow assembler code to access members of and the 'fp_regs'
  * structure at their correct offsets.
  ******************************************************************************/
-#if CTX_INCLUDE_FPREGS
 #define CTX_FPREGS_OFFSET	(CTX_SYSREGS_OFFSET + CTX_SYSREGS_END)
+#if CTX_INCLUDE_FPREGS
 #define CTX_FP_Q0		U(0x0)
 #define CTX_FP_Q1		U(0x10)
 #define CTX_FP_Q2		U(0x20)
@@ -170,8 +170,14 @@
 #else
 #define CTX_FPREGS_END		U(0x210) /* Align to the next 16 byte boundary */
 #endif
+#else
+#define CTX_FPREGS_END		U(0)
 #endif
 
+#define CTX_CVE_2018_3639_OFFSET	(CTX_FPREGS_OFFSET + CTX_FPREGS_END)
+#define CTX_CVE_2018_3639_DISABLE	U(0)
+#define CTX_CVE_2018_3639_END		U(0x10) /* Align to the next 16 byte boundary */
+
 #ifndef __ASSEMBLY__
 
 #include <cassert.h>
@@ -195,6 +201,7 @@
 #define CTX_FPREG_ALL		(CTX_FPREGS_END >> DWORD_SHIFT)
 #endif
 #define CTX_EL3STATE_ALL	(CTX_EL3STATE_END >> DWORD_SHIFT)
+#define CTX_CVE_2018_3639_ALL	(CTX_CVE_2018_3639_END >> DWORD_SHIFT)
 
 /*
  * AArch64 general purpose register context structure. Usually x0-x18,
@@ -227,6 +234,9 @@ DEFINE_REG_STRUCT(fp_regs, CTX_FPREG_ALL);
  */
 DEFINE_REG_STRUCT(el3_state, CTX_EL3STATE_ALL);
 
+/* Function pointer used by CVE-2018-3639 dynamic mitigation */
+DEFINE_REG_STRUCT(cve_2018_3639, CTX_CVE_2018_3639_ALL);
+
 /*
  * Macros to access members of any of the above structures using their
  * offsets
@@ -251,6 +261,7 @@ typedef struct cpu_context {
 #if CTX_INCLUDE_FPREGS
 	fp_regs_t fpregs_ctx;
 #endif
+	cve_2018_3639_t cve_2018_3639_ctx;
 } cpu_context_t;
 
 /* Macros to access members of the 'cpu_context_t' structure */
@@ -276,6 +287,8 @@ CASSERT(CTX_FPREGS_OFFSET == __builtin_offsetof(cpu_context_t, fpregs_ctx), \
 #endif
 CASSERT(CTX_EL3STATE_OFFSET == __builtin_offsetof(cpu_context_t, el3state_ctx), \
 	assert_core_context_el3state_offset_mismatch);
+CASSERT(CTX_CVE_2018_3639_OFFSET == __builtin_offsetof(cpu_context_t, cve_2018_3639_ctx), \
+	assert_core_context_cve_2018_3639_offset_mismatch);
 
 /*
  * Helper macro to set the general purpose registers that correspond to

lib/cpus/aarch64/cortex_a57.S

@@ -573,8 +573,9 @@ func cortex_a57_cpu_reg_dump
 	ret
 endfunc cortex_a57_cpu_reg_dump
 
-declare_cpu_ops_workaround_cve_2017_5715 cortex_a57, CORTEX_A57_MIDR, \
+declare_cpu_ops_wa cortex_a57, CORTEX_A57_MIDR, \
 	cortex_a57_reset_func, \
 	check_errata_cve_2017_5715, \
+	CPU_NO_EXTRA2_FUNC, \
 	cortex_a57_core_pwr_dwn, \
 	cortex_a57_cluster_pwr_dwn

lib/cpus/aarch64/cortex_a72.S

@@ -310,8 +310,9 @@ func cortex_a72_cpu_reg_dump
 	ret
 endfunc cortex_a72_cpu_reg_dump
 
-declare_cpu_ops_workaround_cve_2017_5715 cortex_a72, CORTEX_A72_MIDR, \
+declare_cpu_ops_wa cortex_a72, CORTEX_A72_MIDR, \
 	cortex_a72_reset_func, \
 	check_errata_cve_2017_5715, \
+	CPU_NO_EXTRA2_FUNC, \
 	cortex_a72_core_pwr_dwn, \
 	cortex_a72_cluster_pwr_dwn

lib/cpus/aarch64/cortex_a73.S

@@ -187,8 +187,9 @@ func cortex_a73_cpu_reg_dump
 	ret
 endfunc cortex_a73_cpu_reg_dump
 
-declare_cpu_ops_workaround_cve_2017_5715 cortex_a73, CORTEX_A73_MIDR, \
+declare_cpu_ops_wa cortex_a73, CORTEX_A73_MIDR, \
 	cortex_a73_reset_func, \
 	check_errata_cve_2017_5715, \
+	CPU_NO_EXTRA2_FUNC, \
 	cortex_a73_core_pwr_dwn, \
 	cortex_a73_cluster_pwr_dwn

lib/cpus/aarch64/cortex_a75.S

@@ -130,7 +130,8 @@ func cortex_a75_cpu_reg_dump
 	ret
 endfunc cortex_a75_cpu_reg_dump
 
-declare_cpu_ops_workaround_cve_2017_5715 cortex_a75, CORTEX_A75_MIDR, \
+declare_cpu_ops_wa cortex_a75, CORTEX_A75_MIDR, \
 	cortex_a75_reset_func, \
 	check_errata_cve_2017_5715, \
+	CPU_NO_EXTRA2_FUNC, \
 	cortex_a75_core_pwr_dwn

lib/cpus/aarch64/cpu_helpers.S

@@ -316,3 +316,27 @@ func check_wa_cve_2017_5715
 	mov	x0, #ERRATA_NOT_APPLIES
 	ret
 endfunc check_wa_cve_2017_5715
+
+/*
+ * void *wa_cve_2018_3639_get_disable_ptr(void);
+ *
+ * Returns a function pointer which is used to disable mitigation
+ * for CVE-2018-3639.
+ * The function pointer is only returned on cores that employ
+ * dynamic mitigation.  If the core uses static mitigation or is
+ * unaffected by CVE-2018-3639 this function returns NULL.
+ *
+ * NOTE: Must be called only after cpu_ops have been initialized
+ *       in per-CPU data.
+ */
+	.globl	wa_cve_2018_3639_get_disable_ptr
+func wa_cve_2018_3639_get_disable_ptr
+	mrs	x0, tpidr_el3
+#if ENABLE_ASSERTIONS
+	cmp	x0, #0
+	ASM_ASSERT(ne)
+#endif
+	ldr	x0, [x0, #CPU_DATA_CPU_OPS_PTR]
+	ldr	x0, [x0, #CPU_EXTRA2_FUNC]
+	ret
+endfunc wa_cve_2018_3639_get_disable_ptr

lib/cpus/cpu-ops.mk

@@ -18,6 +18,7 @@ A57_DISABLE_NON_TEMPORAL_HINT	?=1
 
 WORKAROUND_CVE_2017_5715	?=1
 WORKAROUND_CVE_2018_3639	?=1
+DYNAMIC_WORKAROUND_CVE_2018_3639	?=0
 
 # Process SKIP_A57_L1_FLUSH_PWR_DWN flag
 $(eval $(call assert_boolean,SKIP_A57_L1_FLUSH_PWR_DWN))
@@ -39,6 +40,15 @@ $(eval $(call add_define,WORKAROUND_CVE_2017_5715))
 $(eval $(call assert_boolean,WORKAROUND_CVE_2018_3639))
 $(eval $(call add_define,WORKAROUND_CVE_2018_3639))
 
+$(eval $(call assert_boolean,DYNAMIC_WORKAROUND_CVE_2018_3639))
+$(eval $(call add_define,DYNAMIC_WORKAROUND_CVE_2018_3639))
+
+ifneq (${DYNAMIC_WORKAROUND_CVE_2018_3639},0)
+    ifeq (${WORKAROUND_CVE_2018_3639},0)
+        $(error "Error: WORKAROUND_CVE_2018_3639 must be 1 if DYNAMIC_WORKAROUND_CVE_2018_3639 is 1")
+    endif
+endif
+
 # CPU Errata Build flags.
 # These should be enabled by the platform if the erratum workaround needs to be
 # applied.

lib/el3_runtime/aarch64/context.S

@@ -404,6 +404,15 @@ func el3_exit
 	msr	spsr_el3, x16
 	msr	elr_el3, x17
 
+#if IMAGE_BL31 && DYNAMIC_WORKAROUND_CVE_2018_3639
+	/* Restore mitigation state as it was on entry to EL3 */
+	ldr	x17, [sp, #CTX_CVE_2018_3639_OFFSET + CTX_CVE_2018_3639_DISABLE]
+	cmp	x17, xzr
+	beq	1f
+	blr	x17
+#endif
+
+1:
 	/* Restore saved general purpose registers and return */
 	b	restore_gp_registers_eret
 endfunc el3_exit

services/arm_arch_svc/arm_arch_svc_setup.c

@@ -11,6 +11,7 @@
 #include <smccc.h>
 #include <smccc_helpers.h>
 #include <wa_cve_2017_5715.h>
+#include <wa_cve_2018_3639.h>
 
 static int32_t smccc_version(void)
 {
@@ -31,7 +32,24 @@ static int32_t smccc_arch_features(u_register_t arg)
 #endif
 #if WORKAROUND_CVE_2018_3639
 	case SMCCC_ARCH_WORKAROUND_2:
+#if DYNAMIC_WORKAROUND_CVE_2018_3639
+		/*
+		 * On a platform where at least one CPU requires
+		 * dynamic mitigation but others are either unaffected
+		 * or permanently mitigated, report the latter as not
+		 * needing dynamic mitigation.
+		 */
+		if (wa_cve_2018_3639_get_disable_ptr() == NULL)
+			return 1;
+		/*
+		 * If we get here, this CPU requires dynamic mitigation
+		 * so report it as such.
+		 */
+		return 0;
+#else
+		/* Either the CPUs are unaffected or permanently mitigated */
 		return SMCCC_ARCH_NOT_REQUIRED;
+#endif
 #endif
 	default:
 		return SMC_UNK;