hw/display/bcm2835_fb: Validate config settings

Validate the config settings that the guest tries to set.

The wiki page documentation is not really accurate here:
generally rather than failing requests to set bad parameters,
the hardware will just clip them to something sensible.

Validate the most important parameters: sizes and
the viewport offsets. This prevents the framebuffer
code from trying to read out-of-range memory.

In the property handling code, we validate the new parameters every
time we encounter a tag that sets them. This means we validate the
config multiple times if the request includes multiple config-setting
tags, but the code would require significant restructuring to do a
validation only once but still return the clipped settings for
get-parameter tags and the buffer allocation tag.

Validation of settings made via the older bcm2835_fb_mbox_push()
function will be done in the next commit.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180814144436.679-8-peter.maydell@linaro.org

1 files changed, 8 insertions, 0 deletions

diff --git a/include/hw/display/bcm2835_fb.h b/include/hw/display/bcm2835_fb.h
index d992c60..228988b 100644
--- a/include/hw/display/bcm2835_fb.h
+++ b/include/hw/display/bcm2835_fb.h
@@ -76,4 +76,12 @@ static inline uint32_t bcm2835_fb_get_size(BCM2835FBConfig *config)
     return yres * bcm2835_fb_get_pitch(config);
 }
 
+/**
+ * bcm2835_fb_validate_config: check provided config
+ *
+ * Validates the configuration information provided by the guest and
+ * adjusts it if necessary.
+ */
+void bcm2835_fb_validate_config(BCM2835FBConfig *config);
+
 #endif