linux-kernel - [PATCH] nv50_disp_chan_mthd: ensure mthd is not NULL

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Date:   Sat, 8 Feb 2020 20:43:27 +0100
From:   Frédéric Pierret 
        <frederic.pierret@...es-os.org>
To:     bskeggs@...hat.com, airlied@...ux.ie, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] nv50_disp_chan_mthd: ensure mthd is not NULL

Pointer to structure array is assumed not NULL by default. It has
the consequence to raise a kernel panic when it's not the case.

Basically, running at least a RTX2080TI on Xen makes a bad mmio error
which causes having 'mthd' pointer to be NULL in 'channv50.c'. From the
code, it's assumed to be not NULL by accessing directly 'mthd->data[0]'
which is the reason of the kernel panic. Simply check if the pointer
is not NULL before continuing.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=206299
Cc: stable@...r.kernel.org
Signed-off-by: Frédéric Pierret (fepitre) <frederic.pierret@...es-os.org>
---
 drivers/gpu/drm/nouveau/nvkm/engine/disp/channv50.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/disp/channv50.c b/drivers/gpu/drm/nouveau/nvkm/engine/disp/channv50.c
index bcf32d92ee5a..50e3539f33d2 100644
--- a/drivers/gpu/drm/nouveau/nvkm/engine/disp/channv50.c
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/disp/channv50.c
@@ -74,6 +74,8 @@ nv50_disp_chan_mthd(struct nv50_disp_chan *chan, int debug)
 
 	if (debug > subdev->debug)
 		return;
+	if (!mthd)
+		return;
 
 	for (i = 0; (list = mthd->data[i].mthd) != NULL; i++) {
 		u32 base = chan->head * mthd->addr;
-- 
2.21.0




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