linux-kernel - [PATCH][next] drm/i915/gvt: fix off-by-one comparison of ring

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Message-Id: <20171204172106.14950-1-colin.king@canonical.com>
Date:   Mon,  4 Dec 2017 17:21:06 +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][next] drm/i915/gvt: fix off-by-one comparison of ring_id

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

The ring_id maximum boundary is being compared using the > operator
instead of >=, leading to an off-by-one error and an out of bounds
write into array vgpu->hws_pga[].  Fix this by simply using the
correct comparison operator. Also re-work another comparison that
uses the comparison > I915_NUM_ENGINES - 1 to use the >= idiom using
to keep this consistent in this code.

Detected by CoverityScan, CID#1462404 ("Out-of-bounds write")

Fixes: a2ae95af9646 ("drm/i915/gvt: update CSB and CSB write pointer in virtual HWSP")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/gpu/drm/i915/gvt/handlers.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/handlers.c b/drivers/gpu/drm/i915/gvt/handlers.c
index 7354ed816f92..c982867e7c2b 100644
--- a/drivers/gpu/drm/i915/gvt/handlers.c
+++ b/drivers/gpu/drm/i915/gvt/handlers.c
@@ -1398,7 +1398,7 @@ static int hws_pga_write(struct intel_vgpu *vgpu, unsigned int offset,
 	 * update the VM CSB status correctly. Here listed registers can
 	 * support BDW, SKL or other platforms with same HWSP registers.
 	 */
-	if (unlikely(ring_id < 0 || ring_id > I915_NUM_ENGINES)) {
+	if (unlikely(ring_id < 0 || ring_id >= I915_NUM_ENGINES)) {
 		gvt_vgpu_err("VM(%d) access unknown hardware status page register:0x%x\n",
 			     vgpu->id, offset);
 		return -EINVAL;
@@ -1473,7 +1473,7 @@ static int elsp_mmio_write(struct intel_vgpu *vgpu, unsigned int offset,
 	u32 data = *(u32 *)p_data;
 	int ret = 0;
 
-	if (WARN_ON(ring_id < 0 || ring_id > I915_NUM_ENGINES - 1))
+	if (WARN_ON(ring_id < 0 || ring_id >= I915_NUM_ENGINES))
 		return -EINVAL;
 
 	execlist = &vgpu->submission.execlist[ring_id];
-- 
2.14.1