linux-kernel - [PATCH] drm/vmwgfx: Fix uninitialized use of dst_pitch in vmw_stdu_bo_cpu

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Date:   Tue, 14 Mar 2023 08:38:08 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     zackr@...are.com
Cc:     linux-graphics-maintainer@...are.com, ndesaulniers@...gle.com,
        trix@...hat.com, krastevm@...are.com, mombasawalam@...are.com,
        tzimmermann@...e.de, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        patches@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] drm/vmwgfx: Fix uninitialized use of dst_pitch in
 vmw_stdu_bo_cpu_commit()

Clang warns (or errors with CONFIG_WERROR):

  drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c:509:29: error: variable 'dst_pitch' is uninitialized when used here [-Werror,-Wuninitialized]
          src_offset = ddirty->top * dst_pitch + ddirty->left * stdu->cpp;
                                     ^~~~~~~~~
  drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c:492:26: note: initialize the variable 'dst_pitch' to silence this warning
          s32 src_pitch, dst_pitch;
                                  ^
                                   = 0
  1 error generated.

The assignments were switched around in such a way that dst_pitch was
used before it was assigned. Swap the pitch assignments to fix the issue
and make it clear which section they are used in.

Fixes: 39985eea5a6d ("drm/vmwgfx: Abstract placement selection")
Link: https://github.com/ClangBuiltLinux/linux/issues/1811
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
I am not sure if this is the right fix, as it was not entirely clear to
me that src_pitch and dst_pitch were being used in the right assignments
but this is the obvious fix otherwise. Consider this a bug report if
not :)
---
 drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c b/drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c
index d79a6eccfaa4..030e977c68e2 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c
@@ -504,11 +504,11 @@ static void vmw_stdu_bo_cpu_commit(struct vmw_kms_dirty *dirty)
 		return;
 
 	/* Assume we are blitting from Guest (bo) to Host (display_srf) */
-	src_pitch = stdu->display_srf->metadata.base_size.width * stdu->cpp;
+	dst_pitch = ddirty->pitch;
 	src_bo = &stdu->display_srf->res.guest_memory_bo->tbo;
 	src_offset = ddirty->top * dst_pitch + ddirty->left * stdu->cpp;
 
-	dst_pitch = ddirty->pitch;
+	src_pitch = stdu->display_srf->metadata.base_size.width * stdu->cpp;
 	dst_bo = &ddirty->buf->tbo;
 	dst_offset = ddirty->fb_top * src_pitch + ddirty->fb_left * stdu->cpp;
 

---
base-commit: c87e859cdeb5d106cb861326e3135c606d61f88d
change-id: 20230314-vmware-wuninitialized-28666fb5a62b

Best regards,
-- 
Nathan Chancellor <nathan@...nel.org>