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hw/display/bcm2835_fb: Validate config settings

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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
This commit is contained in:
Peter Maydell 2018-08-24 13:17:50 +01:00
parent 01f18af98b
commit f8add62c0c
3 changed files with 81 additions and 29 deletions
Download patch file Download diff file Expand all files Collapse all files

48
hw/display/bcm2835_fb.c
View file

@ -34,6 +34,13 @@
#define DEFAULT_VCRAM_SIZE 0x4000000
#define BCM2835_FB_OFFSET 0x00100000
/* Maximum permitted framebuffer size; experimentally determined on an rpi2 */
#define XRES_MAX 3840
#define YRES_MAX 2560
/* Framebuffer size used if guest requests zero size */
#define XRES_SMALL 592
#define YRES_SMALL 488
static void fb_invalidate_display(void *opaque)
{
BCM2835FBState *s = BCM2835_FB(opaque);
@ -202,6 +209,45 @@ static void fb_update_display(void *opaque)
s->invalidate = false;
}
void bcm2835_fb_validate_config(BCM2835FBConfig *config)
{
/*
* Validate the config, and clip any bogus values into range,
* as the hardware does. Note that fb_update_display() relies on
* this happening to prevent it from performing out-of-range
* accesses on redraw.
*/
config->xres = MIN(config->xres, XRES_MAX);
config->xres_virtual = MIN(config->xres_virtual, XRES_MAX);
config->yres = MIN(config->yres, YRES_MAX);
config->yres_virtual = MIN(config->yres_virtual, YRES_MAX);
/*
* These are not minima: a 40x40 framebuffer will be accepted.
* They're only used as defaults if the guest asks for zero size.
*/
if (config->xres == 0) {
config->xres = XRES_SMALL;
}
if (config->yres == 0) {
config->yres = YRES_SMALL;
}
if (config->xres_virtual == 0) {
config->xres_virtual = config->xres;
}
if (config->yres_virtual == 0) {
config->yres_virtual = config->yres;
}
if (fb_use_offsets(config)) {
/* Clip the offsets so the viewport is within the physical screen */
config->xoffset = MIN(config->xoffset,
config->xres_virtual - config->xres);
config->yoffset = MIN(config->yoffset,
config->yres_virtual - config->yres);
}
}
static void bcm2835_fb_mbox_push(BCM2835FBState *s, uint32_t value)
{
uint32_t pitch;
@ -238,8 +284,6 @@ void bcm2835_fb_reconfigure(BCM2835FBState *s, BCM2835FBConfig *newconfig)
{
s->lock = true;
/* TODO: input validation! */
s->config = *newconfig;
s->invalidate = true;