SDEI: Make dispatches synchronous

SDEI event dispatches currently only sets up the Non-secure context
before returning to the caller. The actual dispatch only happens upon
exiting EL3 next time.

However, for various error handling scenarios, it's beneficial to have
the dispatch happen synchronously. I.e. when receiving SDEI interrupt,
or for a successful sdei_dispatch_event() call, the event handler is
executed; and upon the event completion, dispatcher execution resumes
after the point of dispatch. The jump primitives introduced in the
earlier patch facilitates this feature.

With this patch:

  - SDEI interrupts and calls to sdei_dispatch_event prepares the NS
    context for event dispatch, then sets a jump point, and immediately
    exits EL3. This results in the client handler executing in
    Non-secure.

  - When the SDEI client completes the dispatched event, the SDEI
    dispatcher does a longjmp to the jump pointer created earlier. For
    the caller of the sdei_dispatch_event() in particular, this would
    appear as if call returned successfully.

The dynamic workaround for CVE_2018_3639 is slightly shifted around as
part of related minor refactoring. It doesn't affect the workaround
functionality.

Documentation updated.

NOTE: This breaks the semantics of the explicit dispatch API, and any
exiting usages should be carefully reviewed.

Change-Id: Ib9c876d27ea2af7fb22de49832e55a0da83da3f9
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

3 files changed, 114 insertions, 74 deletions

diff --git a/services/std_svc/sdei/sdei_dispatch.S b/services/std_svc/sdei/sdei_dispatch.S
new file mode 100644
index 00000000..a7a4a40f
--- /dev/null
+++ b/services/std_svc/sdei/sdei_dispatch.S
@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <asm_macros.S>
+
+	.globl	begin_sdei_synchronous_dispatch
+
+/*
+ * void begin_sdei_synchronous_dispatch(struct jmpbuf *buffer);
+ *
+ * Begin SDEI dispatch synchronously by setting up a jump point, and exiting
+ * EL3. This jump point is jumped to by the dispatcher after the event is
+ * completed by the client.
+ */
+func begin_sdei_synchronous_dispatch
+	stp	x30, xzr, [sp, #-16]!
+	bl	setjmp
+	cbz	x0, 1f
+	ldp	x30, xzr, [sp], #16
+	ret
+1:
+	b	el3_exit
+endfunc begin_sdei_synchronous_dispatch
diff --git a/services/std_svc/sdei/sdei_intr_mgmt.c b/services/std_svc/sdei/sdei_intr_mgmt.c
index d6324b9c..6acb1295 100644
--- a/services/std_svc/sdei/sdei_intr_mgmt.c
+++ b/services/std_svc/sdei/sdei_intr_mgmt.c
@@ -31,9 +31,8 @@
 /* Structure to store information about an outstanding dispatch */
 typedef struct sdei_dispatch_context {
 	sdei_ev_map_t *map;
-	unsigned int sec_state;
-	unsigned int intr_raw;
 	uint64_t x[SDEI_SAVED_GPREGS];
+	struct jmpbuf *dispatch_jmp;
 
 	/* Exception state registers */
 	uint64_t elr_el3;
@@ -153,8 +152,8 @@ static sdei_dispatch_context_t *get_outstanding_dispatch(void)
 	return &state->dispatch_stack[state->stack_top - 1];
 }
 
-static void save_event_ctx(sdei_ev_map_t *map, void *tgt_ctx, int sec_state,
-		unsigned int intr_raw)
+static sdei_dispatch_context_t *save_event_ctx(sdei_ev_map_t *map,
+		void *tgt_ctx)
 {
 	sdei_dispatch_context_t *disp_ctx;
 	gp_regs_t *tgt_gpregs;
@@ -166,26 +165,14 @@ static void save_event_ctx(sdei_ev_map_t *map, void *tgt_ctx, int sec_state,
 
 	disp_ctx = push_dispatch();
 	assert(disp_ctx);
-	disp_ctx->sec_state = sec_state;
 	disp_ctx->map = map;
-	disp_ctx->intr_raw = intr_raw;
 
 	/* Save general purpose and exception registers */
 	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
+	return disp_ctx;
 }
 
 static void restore_event_ctx(sdei_dispatch_context_t *disp_ctx, void *tgt_ctx)
@@ -249,13 +236,12 @@ static cpu_context_t *restore_and_resume_ns_context(void)
  * SDEI client.
  */
 static void setup_ns_dispatch(sdei_ev_map_t *map, sdei_entry_t *se,
-		cpu_context_t *ctx, int sec_state_to_resume,
-		unsigned int intr_raw)
+		cpu_context_t *ctx, struct jmpbuf *dispatch_jmp)
 {
-	el3_state_t *el3_ctx = get_el3state_ctx(ctx);
+	sdei_dispatch_context_t *disp_ctx;
 
 	/* Push the event and context */
-	save_event_ctx(map, ctx, sec_state_to_resume, intr_raw);
+	disp_ctx = save_event_ctx(map, ctx);
 
 	/*
 	 * Setup handler arguments:
@@ -267,8 +253,8 @@ static void setup_ns_dispatch(sdei_ev_map_t *map, sdei_entry_t *se,
 	 */
 	SMC_SET_GP(ctx, CTX_GPREG_X0, map->ev_num);
 	SMC_SET_GP(ctx, CTX_GPREG_X1, se->arg);
-	SMC_SET_GP(ctx, CTX_GPREG_X2, read_ctx_reg(el3_ctx, CTX_ELR_EL3));
-	SMC_SET_GP(ctx, CTX_GPREG_X3, read_ctx_reg(el3_ctx, CTX_SPSR_EL3));
+	SMC_SET_GP(ctx, CTX_GPREG_X2, disp_ctx->elr_el3);
+	SMC_SET_GP(ctx, CTX_GPREG_X3, disp_ctx->spsr_el3);
 
 	/*
 	 * Prepare for ERET:
@@ -279,6 +265,20 @@ static void setup_ns_dispatch(sdei_ev_map_t *map, sdei_entry_t *se,
 	cm_set_elr_spsr_el3(NON_SECURE, (uintptr_t) se->ep,
 			SPSR_64(sdei_client_el(), MODE_SP_ELX,
 				DISABLE_ALL_EXCEPTIONS));
+
+#if DYNAMIC_WORKAROUND_CVE_2018_3639
+	cve_2018_3639_t *tgt_cve_2018_3639;
+	tgt_cve_2018_3639 = get_cve_2018_3639_ctx(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
+
+	disp_ctx->dispatch_jmp = dispatch_jmp;
 }
 
 /* Handle a triggered SDEI interrupt while events were masked on this PE */
@@ -348,6 +348,7 @@ int sdei_intr_handler(uint32_t intr_raw, uint32_t flags, void *handle,
 	unsigned int sec_state;
 	sdei_cpu_state_t *state;
 	uint32_t intr;
+	struct jmpbuf dispatch_jmp;
 
 	/*
 	 * To handle an event, the following conditions must be true:
@@ -481,29 +482,60 @@ int sdei_intr_handler(uint32_t intr_raw, uint32_t flags, void *handle,
 		ctx = restore_and_resume_ns_context();
 	}
 
-	setup_ns_dispatch(map, se, ctx, sec_state, intr_raw);
+	/* Synchronously dispatch event */
+	setup_ns_dispatch(map, se, ctx, &dispatch_jmp);
+	begin_sdei_synchronous_dispatch(&dispatch_jmp);
+
+	/*
+	 * We reach here when client completes the event.
+	 *
+	 * If the cause of dispatch originally interrupted the Secure world, and
+	 * if Non-secure world wasn't allowed to preempt Secure execution,
+	 * resume Secure.
+	 *
+	 * No need to save the Non-secure context ahead of a world switch: the
+	 * Non-secure context was fully saved before dispatch, and has been
+	 * returned to its pre-dispatch state.
+	 */
+	if ((sec_state == SECURE) && (ehf_is_ns_preemption_allowed() == 0))
+		restore_and_resume_secure_context();
 
 	/*
-	 * End of interrupt is done in sdei_event_complete, when the client
-	 * signals completion.
+	 * The event was dispatched after receiving SDEI interrupt. With
+	 * the event handling completed, EOI the corresponding
+	 * interrupt.
 	 */
+	if ((map->ev_num != SDEI_EVENT_0) && is_map_bound(map)) {
+		ERROR("Invalid SDEI mapping: ev=%u\n", map->ev_num);
+		panic();
+	}
+	plat_ic_end_of_interrupt(intr_raw);
+
+	if (is_event_shared(map))
+		sdei_map_unlock(map);
+
 	return 0;
 }
 
-/* Explicitly dispatch the given SDEI event */
-int sdei_dispatch_event(int ev_num, unsigned int preempted_sec_state)
+/*
+ * Explicitly dispatch the given SDEI event.
+ *
+ * When calling this API, the caller must be prepared for the SDEI dispatcher to
+ * restore and make Non-secure context as active. This call returns only after
+ * the client has completed the dispatch. Then, the Non-secure context will be
+ * active, and the following ERET will return to Non-secure.
+ *
+ * Should the caller require re-entry to Secure, it must restore the Secure
+ * context and program registers for ERET.
+ */
+int sdei_dispatch_event(int ev_num)
 {
 	sdei_entry_t *se;
 	sdei_ev_map_t *map;
-	cpu_context_t *ctx;
+	cpu_context_t *ns_ctx;
 	sdei_dispatch_context_t *disp_ctx;
 	sdei_cpu_state_t *state;
-
-	/* Validate preempted security state */
-	if ((preempted_sec_state != SECURE) &&
-			(preempted_sec_state != NON_SECURE)) {
-		return -1;
-	}
+	struct jmpbuf dispatch_jmp;
 
 	/* Can't dispatch if events are masked on this PE */
 	state = sdei_get_this_pe_state();
@@ -549,21 +581,31 @@ int sdei_dispatch_event(int ev_num, unsigned int preempted_sec_state)
 	ehf_activate_priority(sdei_event_priority(map));
 
 	/*
-	 * We assume the current context is SECURE, and that it's already been
-	 * saved.
+	 * Prepare for NS dispatch by restoring the Non-secure context and
+	 * marking that as active.
 	 */
-	ctx = restore_and_resume_ns_context();
+	ns_ctx = restore_and_resume_ns_context();
+
+	/* Dispatch event synchronously */
+	setup_ns_dispatch(map, se, ns_ctx, &dispatch_jmp);
+	begin_sdei_synchronous_dispatch(&dispatch_jmp);
 
 	/*
-	 * The caller has effectively terminated execution. Record to resume the
-	 * preempted context later when the event completes or
-	 * complete-and-resumes.
+	 * We reach here when client completes the event.
+	 *
+	 * Deactivate the priority level that was activated at the time of
+	 * explicit dispatch.
 	 */
-	setup_ns_dispatch(map, se, ctx, preempted_sec_state, 0);
+	ehf_deactivate_priority(sdei_event_priority(map));
 
 	return 0;
 }
 
+static void end_sdei_explicit_dispatch(struct jmpbuf *buffer)
+{
+	longjmp(buffer);
+}
+
 int sdei_event_complete(int resume, uint64_t pc)
 {
 	sdei_dispatch_context_t *disp_ctx;
@@ -636,38 +678,8 @@ int sdei_event_complete(int resume, uint64_t pc)
 		}
 	}
 
-	/*
-	 * If the cause of dispatch originally interrupted the Secure world, and
-	 * if Non-secure world wasn't allowed to preempt Secure execution,
-	 * resume Secure.
-	 *
-	 * No need to save the Non-secure context ahead of a world switch: the
-	 * Non-secure context was fully saved before dispatch, and has been
-	 * returned to its pre-dispatch state.
-	 */
-	if ((disp_ctx->sec_state == SECURE) &&
-			(ehf_is_ns_preemption_allowed() == 0)) {
-		restore_and_resume_secure_context();
-	}
-
-	if ((map->ev_num == SDEI_EVENT_0) || is_map_bound(map)) {
-		/*
-		 * The event was dispatched after receiving SDEI interrupt. With
-		 * the event handling completed, EOI the corresponding
-		 * interrupt.
-		 */
-		plat_ic_end_of_interrupt(disp_ctx->intr_raw);
-	} else {
-		/*
-		 * An unbound event must have been dispatched explicitly.
-		 * Deactivate the priority level that was activated at the time
-		 * of explicit dispatch.
-		 */
-		ehf_deactivate_priority(sdei_event_priority(map));
-	}
-
-	if (is_event_shared(map))
-		sdei_map_unlock(map);
+	/* End the outstanding dispatch */
+	end_sdei_explicit_dispatch(disp_ctx->dispatch_jmp);
 
 	return 0;
 }
diff --git a/services/std_svc/sdei/sdei_private.h b/services/std_svc/sdei/sdei_private.h
index ec4148c6..ea602878 100644
--- a/services/std_svc/sdei/sdei_private.h
+++ b/services/std_svc/sdei/sdei_private.h
@@ -14,6 +14,7 @@
 #include <interrupt_mgmt.h>
 #include <platform.h>
 #include <sdei.h>
+#include <setjmp.h>
 #include <spinlock.h>
 #include <stdbool.h>
 #include <types.h>
@@ -240,5 +241,6 @@ unsigned int sdei_pe_mask(void);
 int sdei_intr_handler(uint32_t intr, uint32_t flags, void *handle,
 		void *cookie);
 bool can_sdei_state_trans(sdei_entry_t *se, sdei_action_t act);
+void begin_sdei_synchronous_dispatch(struct jmpbuf *buffer);
 
 #endif /* __SDEI_PRIVATE_H__ */