[Mesa-dev] [PATCH] i965: fix problem with constant out of bounds access (v3)

[Dave Airlie]

Okay I now understand why Frank would want to run away, this is
my attempt at fixing the CVE out of bounds access to constants
outside the range. This attempt converts any illegal constants
to constant 0 as per the GL spec, and is undefined behaviour.

A future patch should add some debug for users to find this out,
but this needs to be backported to stable branches.

CVE-2013-1872

v2: drop the last hunk which was a separate fix (now in master).
hopefully fix the indentations.

v3: don't fail piglit, the whole 8/16 dispatch stuff was over
my head, and I spent a while figuring it out, but this one is
definitely safe, one piglit pass extra on my Ironlake.

NOTE: This is a candidate for stable branches.
---
 src/mesa/drivers/dri/i965/brw_fs.cpp         | 15 ++++++++++++++-
 src/mesa/drivers/dri/i965/brw_fs.h           |  1 +
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp |  1 +
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index baaa25c..7f8edff 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -818,6 +818,7 @@ fs_visitor::import_uniforms(fs_visitor *v)
 			   import_uniforms_callback,
 			   variable_ht);
    this->params_remap = v->params_remap;
+   this->nr_params_remap = v->nr_params_remap;
 }
 
 /* Our support for uniforms is piggy-backed on the struct
@@ -1490,6 +1491,7 @@ fs_visitor::remove_dead_constants()
 {
    if (dispatch_width == 8) {
       this->params_remap = ralloc_array(mem_ctx, int, c->prog_data.nr_params);
+      this->nr_params_remap = c->prog_data.nr_params;
 
       for (unsigned int i = 0; i < c->prog_data.nr_params; i++)
 	 this->params_remap[i] = -1;
@@ -1504,7 +1506,14 @@ fs_visitor::remove_dead_constants()
 	    if (inst->src[i].file != UNIFORM)
 	       continue;
 
-	    assert(constant_nr < (int)c->prog_data.nr_params);
+	    /* Section 5.11 of the OpenGL 4.3 spec says:
+	     *
+	     *     "Out-of-bounds reads return undefined values, which include
+	     *     values from other variables of the active program or zero."
+	     */
+	    if (constant_nr < 0 || constant_nr >= (int)c->prog_data.nr_params) {
+	       constant_nr = 0;
+	    }
 
 	    /* For now, set this to non-negative.  We'll give it the
 	     * actual new number in a moment, in order to keep the
@@ -1552,6 +1561,10 @@ fs_visitor::remove_dead_constants()
 	 if (inst->src[i].file != UNIFORM)
 	    continue;
 
+	 /* as above alias to 0 */
+	 if (constant_nr < 0 || constant_nr >= (int)this->nr_params_remap) {
+	    constant_nr = 0;
+	 }
 	 assert(this->params_remap[constant_nr] != -1);
 	 inst->src[i].reg = this->params_remap[constant_nr];
 	 inst->src[i].reg_offset = 0;
diff --git a/src/mesa/drivers/dri/i965/brw_fs.h b/src/mesa/drivers/dri/i965/brw_fs.h
index 3d44daf..762e250 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.h
+++ b/src/mesa/drivers/dri/i965/brw_fs.h
@@ -440,6 +440,7 @@ public:
     * uniform index.
     */
    int *params_remap;
+   int nr_params_remap;
 
    struct hash_table *variable_ht;
    fs_reg frag_depth;
diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 79c5a11..9bb15d0 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -2464,6 +2464,7 @@ fs_visitor::fs_visitor(struct brw_context *brw,
    this->live_intervals_valid = false;
 
    this->params_remap = NULL;
+   this->nr_params_remap = 0;
 
    this->force_uncompressed_stack = 0;
    this->force_sechalf_stack = 0;
-- 
1.8.1.4