From b18224e95cb13ef7517aa26e6b47c85117327f11 Mon Sep 17 00:00:00 2001
From: Michal Srb <msrb@suse.com>
Date: Mon, 5 Feb 2018 16:04:37 +0000
Subject: [PATCH] drm/i915/cmdparser: Check reg_table_count before derefencing.
Git-commit: b18224e95cb13ef7517aa26e6b47c85117327f11
Patch-mainline: v4.16-rc1
References: FATE#322643 bsc#1055900
No-fix: 2f265fad9756a40c09e3f4dcc62d5d7fa73a9fb2

The find_reg function was assuming that there is always at least one table in
reg_tables. It is not always true.

In case of VCS or VECS, the reg_tables is NULL and reg_table_count is 0,
implying that no register-accessing commands are allowed. However, the command
tables include commands such as MI_STORE_REGISTER_MEM. When trying to check
such command, the find_reg would dereference NULL pointer.

Now it will just return NULL meaning that the register was not found and the
command will be rejected.

Fixes: 76ff480ec963 ("drm/i915/cmdparser: Use binary search for faster register lookup")
Signed-off-by: Michal Srb <msrb@suse.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180205142916.27092-2-msrb@suse.com
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180205160438.3267-1-chris@chris-wilson.co.uk
register lookup")
(cherry picked from commit 2f265fad9756a40c09e3f4dcc62d5d7fa73a9fb2)

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/i915_cmd_parser.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/i915/i915_cmd_parser.c
+++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
@@ -1032,7 +1032,7 @@ find_reg(const struct intel_engine_cs *e
 	const struct drm_i915_reg_table *table = engine->reg_tables;
 	int count = engine->reg_table_count;
 
-	do {
+	for (; count > 0; ++table, --count) {
 		if (!table->master || is_master) {
 			const struct drm_i915_reg_descriptor *reg;
 
@@ -1040,7 +1040,7 @@ find_reg(const struct intel_engine_cs *e
 			if (reg != NULL)
 				return reg;
 		}
-	} while (table++, --count);
+	}
 
 	return NULL;
 }