[PATCH 4.9 01/24] drm/vc4: Fix termination of the initial scan for branch targets.

Greg Kroah-Hartman
2017-03-24T18:24:07Z

From: Eric Anholt <eric@anholt.net>

commit 457e67a728696c4f8e6423c64e93def50530db9a upstream.

The loop is scanning until the original max_ip (size of the BO), but
we want to not examine any code after the PROG_END's delay slots.
There was a block trying to do that, except that we had some early
continue statements if the signal wasn't a PROG_END or a BRANCH.

The failure mode would be that a valid shader is rejected because some
undefined memory after the PROG_END slots is parsed as a branch and
the rest of its setup is illegal. I haven't seen this in the wild,
but valgrind was complaining when about this up in the userland
simulator mode.

Signed-off-by: Eric Anholt <eric@anholt.net>
Cc: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/vc4/vc4_validate_shaders.c | 19 ++++++++-----------
1 file changed, 8 insertions(+), 11 deletions(-)

--- a/drivers/gpu/drm/vc4/vc4_validate_shaders.c
+++ b/drivers/gpu/drm/vc4/vc4_validate_shaders.c
@@ -608,9 +608,7 @@ static bool
vc4_validate_branches(struct vc4_shader_validation_state *validation_state)
{
uint32_t max_branch_target = 0;
- bool found_shader_end = false;
int ip;
- int shader_end_ip = 0;
int last_branch = -2;

for (ip = 0; ip < validation_state->max_ip; ip++) {
@@ -621,8 +619,13 @@ vc4_validate_branches(struct vc4_shader_
uint32_t branch_target_ip;

if (sig == QPU_SIG_PROG_END) {
- shader_end_ip = ip;
- found_shader_end = true;
+ /* There are two delay slots after program end is
+ * signaled that are still executed, then we're
+ * finished. validation_state->max_ip is the
+ * instruction after the last valid instruction in the
+ * program.
+ */
+ validation_state->max_ip = ip + 3;
continue;
}

@@ -676,15 +679,9 @@ vc4_validate_branches(struct vc4_shader_
}
set_bit(after_delay_ip, validation_state->branch_targets);
max_branch_target = max(max_branch_target, after_delay_ip);
-
- /* There are two delay slots after program end is signaled
- * that are still executed, then we're finished.
- */
- if (found_shader_end && ip == shader_end_ip + 2)
- break;
}

- if (max_branch_target > shader_end_ip) {
+ if (max_branch_target > validation_state->max_ip - 3) {
DRM_ERROR("Branch landed after QPU_SIG_PROG_END");
return false;
}