drm/nv50/fb: Fix nullptr-deref on IGPs

When COMP_MAX_TAG == 0, the tags mm was uninitialised. Fixed by initialising with zero length.

v2: Fix style error

Signed-off-by: Roy Spliet <r.spliet@student.tudelft.nl>
Tested-by: Roy Spliet <r.spliet@student.tudelft.nl>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

2 files changed, 5 insertions, 4 deletions

diff --git a/drivers/gpu/drm/nouveau/core/subdev/fb/base.c b/drivers/gpu/drm/nouveau/core/subdev/fb/base.c
index d6d16007ec1a..d62045f454b2 100644
--- a/drivers/gpu/drm/nouveau/core/subdev/fb/base.c
+++ b/drivers/gpu/drm/nouveau/core/subdev/fb/base.c
@@ -86,8 +86,8 @@ nouveau_fb_preinit(struct nouveau_fb *pfb)
                         return ret;
         }
 
-        if (!nouveau_mm_initialised(&pfb->tags) && tags) {
-                ret = nouveau_mm_init(&pfb->tags, 0, ++tags, 1);
+        if (!nouveau_mm_initialised(&pfb->tags)) {
+                ret = nouveau_mm_init(&pfb->tags, 0, tags ? ++tags : 0, 1);
                 if (ret)
                         return ret;
         }
diff --git a/drivers/gpu/drm/nouveau/core/subdev/fb/nv50.c b/drivers/gpu/drm/nouveau/core/subdev/fb/nv50.c
index 487cb8c6c204..eac236ed19b2 100644
--- a/drivers/gpu/drm/nouveau/core/subdev/fb/nv50.c
+++ b/drivers/gpu/drm/nouveau/core/subdev/fb/nv50.c
@@ -99,7 +99,7 @@ nv50_fb_vram_init(struct nouveau_fb *pfb)
         struct nouveau_bios *bios = nouveau_bios(device);
         const u32 rsvd_head = ( 256 * 1024) >> 12; /* vga memory */
         const u32 rsvd_tail = (1024 * 1024) >> 12; /* vbios etc */
-        u32 size;
+        u32 size, tags = 0;
         int ret;
 
         pfb->ram.size = nv_rd32(pfb, 0x10020c);
@@ -140,10 +140,11 @@ nv50_fb_vram_init(struct nouveau_fb *pfb)
                         return ret;
 
                 pfb->ram.ranks = (nv_rd32(pfb, 0x100200) & 0x4) ? 2 : 1;
+                tags = nv_rd32(pfb, 0x100320);
                 break;
         }
 
-        return nv_rd32(pfb, 0x100320);
+        return tags;
 }
 
 static int