From: Arnd Bergmann <arnd@arndb.de>

When CONFIG_SYSFB is disabled, the hyperv_fb driver can now run into
undefined behavior on a gen2 VM, as indicated by this smatch warning:

drivers/video/fbdev/hyperv_fb.c:1077 hvfb_getmem() error: uninitialized symbol 'base'.
drivers/video/fbdev/hyperv_fb.c:1077 hvfb_getmem() error: uninitialized symbol 'size'.

Since there is no way to know the actual framebuffer in this configuration,
just return an allocation failure here, which should avoid the build
warning and the undefined behavior.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202311070802.YCpvehaz-lkp@intel.com/
Fixes: a07b50d80ab6 ("hyperv: avoid dependency on screen_info")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/video/fbdev/hyperv_fb.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
index bf59daf862fc..a80939fe2ee6 100644
--- a/drivers/video/fbdev/hyperv_fb.c
+++ b/drivers/video/fbdev/hyperv_fb.c
@@ -1013,6 +1013,8 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
 	} else if (IS_ENABLED(CONFIG_SYSFB)) {
 		base = screen_info.lfb_base;
 		size = screen_info.lfb_size;
+	} else {
+		goto err1;
 	}
 
 	/*
-- 
2.39.2

On 11/8/23 15:58, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> When CONFIG_SYSFB is disabled, the hyperv_fb driver can now run into
> undefined behavior on a gen2 VM, as indicated by this smatch warning:
>
> drivers/video/fbdev/hyperv_fb.c:1077 hvfb_getmem() error: uninitialized symbol 'base'.
> drivers/video/fbdev/hyperv_fb.c:1077 hvfb_getmem() error: uninitialized symbol 'size'.
>
> Since there is no way to know the actual framebuffer in this configuration,
> just return an allocation failure here, which should avoid the build
> warning and the undefined behavior.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Closes: https://lore.kernel.org/r/202311070802.YCpvehaz-lkp@intel.com/
> Fixes: a07b50d80ab6 ("hyperv: avoid dependency on screen_info")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

applied.

Thanks!
Helge


> ---
>   drivers/video/fbdev/hyperv_fb.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
> index bf59daf862fc..a80939fe2ee6 100644
> --- a/drivers/video/fbdev/hyperv_fb.c
> +++ b/drivers/video/fbdev/hyperv_fb.c
> @@ -1013,6 +1013,8 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
>   	} else if (IS_ENABLED(CONFIG_SYSFB)) {
>   		base = screen_info.lfb_base;
>   		size = screen_info.lfb_size;
> +	} else {
> +		goto err1;
>   	}
>
>   	/*