SDEI: Ensure SDEI handler executes with CVE-2018-3639 mitigation enabled

When dynamic mitigation is used, the SDEI handler is required to
execute with the mitigation enabled by default, regardless of the
mitigation state for lower ELs.  This means that if the kernel or
hypervisor explicitly disables the mitigation and then later when the
event is dispatched, the dispatcher will remember the mitigation state
for the lower ELs but force the mitigation to be on during the SDEI
handler execution.  When the SDEI handler returns, it will restore the
mitigation state.

This behaviour is described in "Firmware interfaces for mitigating
cache speculation vulnerabilities System Software on Arm Systems"[0].

[0] https://developer.arm.com/cache-speculation-vulnerability-firmware-specification

Change-Id: I8dd60b736be0aa9e832b0f92d67a401fdeb417f4
Signed-off-by: Dimitris Papastamos <dimitris.papastamos@arm.com>

include/lib/el3_runtime/aarch64/context.h

@@ -271,6 +271,7 @@ typedef struct cpu_context {
 #endif
 #define get_sysregs_ctx(h)	(&((cpu_context_t *) h)->sysregs_ctx)
 #define get_gpregs_ctx(h)	(&((cpu_context_t *) h)->gpregs_ctx)
+#define get_cve_2018_3639_ctx(h)	(&((cpu_context_t *) h)->cve_2018_3639_ctx)
 
 /*
  * Compile time assertions related to the 'cpu_context' structure to

services/std_svc/sdei/sdei_intr_mgmt.c

@@ -39,6 +39,11 @@ typedef struct sdei_dispatch_context {
 	/* Exception state registers */
 	uint64_t elr_el3;
 	uint64_t spsr_el3;
+
+#if DYNAMIC_WORKAROUND_CVE_2018_3639
+	/* CVE-2018-3639 mitigation state */
+	uint64_t disable_cve_2018_3639;
+#endif
 } sdei_dispatch_context_t;
 
 /* Per-CPU SDEI state data */
@@ -170,6 +175,18 @@ static void save_event_ctx(sdei_ev_map_t *map, void *tgt_ctx, int sec_state,
 	memcpy(disp_ctx->x, tgt_gpregs, sizeof(disp_ctx->x));
 	disp_ctx->spsr_el3 = read_ctx_reg(tgt_el3, CTX_SPSR_EL3);
 	disp_ctx->elr_el3 = read_ctx_reg(tgt_el3, CTX_ELR_EL3);
+
+#if DYNAMIC_WORKAROUND_CVE_2018_3639
+	cve_2018_3639_t *tgt_cve_2018_3639;
+	tgt_cve_2018_3639 = get_cve_2018_3639_ctx(tgt_ctx);
+
+	/* Save CVE-2018-3639 mitigation state */
+	disp_ctx->disable_cve_2018_3639 = read_ctx_reg(tgt_cve_2018_3639,
+		CTX_CVE_2018_3639_DISABLE);
+
+	/* Force SDEI handler to execute with mitigation enabled by default */
+	write_ctx_reg(tgt_cve_2018_3639, CTX_CVE_2018_3639_DISABLE, 0);
+#endif
 }
 
 static void restore_event_ctx(sdei_dispatch_context_t *disp_ctx, void *tgt_ctx)
@@ -188,6 +205,15 @@ static void restore_event_ctx(sdei_dispatch_context_t *disp_ctx, void *tgt_ctx)
 	memcpy(tgt_gpregs, disp_ctx->x, sizeof(disp_ctx->x));
 	write_ctx_reg(tgt_el3, CTX_SPSR_EL3, disp_ctx->spsr_el3);
 	write_ctx_reg(tgt_el3, CTX_ELR_EL3, disp_ctx->elr_el3);
+
+#if DYNAMIC_WORKAROUND_CVE_2018_3639
+	cve_2018_3639_t *tgt_cve_2018_3639;
+	tgt_cve_2018_3639 = get_cve_2018_3639_ctx(tgt_ctx);
+
+	/* Restore CVE-2018-3639 mitigation state */
+	write_ctx_reg(tgt_cve_2018_3639, CTX_CVE_2018_3639_DISABLE,
+		disp_ctx->disable_cve_2018_3639);
+#endif
 }
 
 static void save_secure_context(void)