linux-kernel - [PATCH] drm/i915/gvt: don't dereference 'workload' before null checking it

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Message-Id: <20180321190653.3829-1-colin.king@canonical.com>
Date:   Wed, 21 Mar 2018 19:06:53 +0000
From:   Colin King <colin.king@...onical.com>
To:     Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/i915/gvt: don't dereference 'workload' before null checking it

From: Colin Ian King <colin.king@...onical.com>

The pointer workload is dereferenced before it is null checked, hence
there is a potential for a null pointer dereference on workload. Fix
this by only dereferencing workload after it is null checked.

Detected by CoverityScan, CID#1466017 ("Dereference before null check")

Fixes: fa3dd623e559 ("drm/i915/gvt: keep oa config in shadow ctx")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/gpu/drm/i915/gvt/scheduler.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/scheduler.c b/drivers/gpu/drm/i915/gvt/scheduler.c
index 068126404151..f3010e365a48 100644
--- a/drivers/gpu/drm/i915/gvt/scheduler.c
+++ b/drivers/gpu/drm/i915/gvt/scheduler.c
@@ -60,9 +60,9 @@ static void set_context_pdp_root_pointer(
 static void sr_oa_regs(struct intel_vgpu_workload *workload,
 		u32 *reg_state, bool save)
 {
-	struct drm_i915_private *dev_priv = workload->vgpu->gvt->dev_priv;
-	u32 ctx_oactxctrl = dev_priv->perf.oa.ctx_oactxctrl_offset;
-	u32 ctx_flexeu0 = dev_priv->perf.oa.ctx_flexeu0_offset;
+	struct drm_i915_private *dev_priv;
+	u32 ctx_oactxctrl;
+	u32 ctx_flexeu0;
 	int i = 0;
 	u32 flex_mmio[] = {
 		i915_mmio_reg_offset(EU_PERF_CNTL0),
@@ -77,6 +77,10 @@ static void sr_oa_regs(struct intel_vgpu_workload *workload,
 	if (!workload || !reg_state || workload->ring_id != RCS)
 		return;
 
+	dev_priv = workload->vgpu->gvt->dev_priv;
+	ctx_oactxctrl = dev_priv->perf.oa.ctx_oactxctrl_offset;
+	ctx_flexeu0 = dev_priv->perf.oa.ctx_flexeu0_offset;
+
 	if (save) {
 		workload->oactxctrl = reg_state[ctx_oactxctrl + 1];
 
-- 
2.15.1