drm/ast: Fixed CVE for DP501

[Bug][DP501]
If ASPEED P2A (PCI to AHB) bridge is disabled and disallowed for
CVE_2019_6260 item3, and then the monitor's EDID is unable read through
Parade DP501.
The reason is the DP501's FW is mapped to BMC addressing space rather
than Host addressing space.
The resolution is that using "pci_iomap_range()" maps to DP501's FW that
stored on the end of FB (Frame Buffer).
In this case, FrameBuffer reserves the last 2MB used for the image of
DP501.

Signed-off-by: KuoHsiang Chou <[email protected]>
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Thomas Zimmermann <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

1 files changed, 10 insertions, 1 deletions

diff --git a/drivers/gpu/drm/ast/ast_main.c b/drivers/gpu/drm/ast/ast_main.c
index c29cc7f19863..189d783f6e2c 100644
--- a/drivers/gpu/drm/ast/ast_main.c
+++ b/drivers/gpu/drm/ast/ast_main.c
@@ -99,7 +99,7 @@ static void ast_detect_config_mode(struct drm_device *dev, u32 *scu_rev)
 	if (!(jregd0 & 0x80) || !(jregd1 & 0x10)) {
 		/* Double check it's actually working */
 		data = ast_read32(ast, 0xf004);
-		if (data != 0xFFFFFFFF) {
+		if ((data != 0xFFFFFFFF) && (data != 0x00)) {
 			/* P2A works, grab silicon revision */
 			ast->config_mode = ast_use_p2a;
 
@@ -411,6 +411,7 @@ struct ast_private *ast_device_create(const struct drm_driver *drv,
 		return ast;
 	dev = &ast->base;
 
+	dev->pdev = pdev;
 	pci_set_drvdata(pdev, dev);
 
 	ast->regs = pcim_iomap(pdev, 1, 0);
@@ -450,6 +451,14 @@ struct ast_private *ast_device_create(const struct drm_driver *drv,
 	if (ret)
 		return ERR_PTR(ret);
 
+	/* map reserved buffer */
+	ast->dp501_fw_buf = NULL;
+	if (dev->vram_mm->vram_size < pci_resource_len(dev->pdev, 0)) {
+		ast->dp501_fw_buf = pci_iomap_range(dev->pdev, 0, dev->vram_mm->vram_size, 0);
+		if (!ast->dp501_fw_buf)
+			drm_info(dev, "failed to map reserved buffer!\n");
+	}
+
 	ret = ast_mode_config_init(ast);
 	if (ret)
 		return ERR_PTR(ret);