[PATCH v4 0/3] Input/SPI: fixes for MacBook8,1 DMA timeout, UAF, and NULL pointer dereference

[PATCH v4 0/3] Input/SPI: fixes for MacBook8,1 DMA timeout, UAF, and NULL pointer dereference

[Shih-Yuan Lee]

Hi Dmitry, Mark, and the linux-input/linux-spi community,

This patch series addresses a long-standing DMA initialization timeout on the 
early 2015 12" MacBook (MacBook8,1) on any boot (including cold boot), as well 
as two pre-existing, high-severity UAF/NULL-pointer bugs in the applespi driver.

Changes in v4:
  - Reverted the runtime `can_dma` callback override from `applespi.c` to avoid 
    architectural layering violation, data races (TOCTOU) with concurrent SPI 
    transfers, and execute-after-free vulnerability upon module unload.
  - Moved the DMI quirk forcing PIO mode for MacBook8,1 to the host PCI glue 
    driver (spi-pxa2xx-pci.c) where LPSS setup occurs.
  - Formatted the DMI match using a structured `pxa2xx_spi_pci_dmi_table` and 
    helper function `pxa2xx_spi_pci_can_dma()`.
  - Added a `force_pio` module parameter in spi-pxa2xx-pci.c to allow other 
    users to manually force PIO mode for debugging.

Changes in v3:
  - Added a `force_pio` module parameter to applespi to allow users to manually 
    disable DMA for SPI transfers.
  - Resolved the execute-after-free vulnerability by unconditionally restoring 
    the original can_dma callback (even if NULL) in the driver remove path.
  - Fixed the probe timing issue by applying the can_dma override at the very 
    beginning of applespi_probe() so that all early initialization transfers 
    safely use PIO mode, and properly restoring it in all probe error paths.
  - Documented the Bugzilla link in the commit message of Patch 1.

Changes in v2:
  - Fixed an unbind/remove execute-after-free vulnerability by storing and 
    restoring the host controller's original can_dma callback in applespi_probe() 
    and applespi_remove().
  - Split the fixes into a 3-patch logical series.

Patch 1 fixes a pre-existing UAF vulnerability in the driver unbind path by 
explicitly calling cancel_work_sync() on the asynchronous registration worker 
work struct before devres frees the driver private data.

Patch 2 fixes a pre-existing race condition in the debugfs interface where 
userspace could open the tp_dim file before the asynchronous worker has 
finished initializing applespi->touchpad_input_dev, leading to a NULL 
pointer dereference. We resolve this using smp_load_acquire() and checking 
for NULL.

Patch 3 introduces a structured DMI quirk and a `force_pio` module parameter 
in spi-pxa2xx-pci.c to disable DMA on MacBook8,1. This forces the controller 
to use the rock-solid PIO mode from the very beginning.

Best regards,
Shih-Yuan Lee

Shih-Yuan Lee (3):
  Input: applespi - cancel pending work on driver remove
  Input: applespi - fix NULL pointer dereference in tp_dim open
  spi: pxa2xx: disable DMA for Apple MacBook8,1

 drivers/input/keyboard/applespi.c | 10 +++++++++-
 drivers/spi/spi-pxa2xx-pci.c      | 33 ++++++++++++++++++++++++++++++-
 2 files changed, 41 insertions(+), 2 deletions(-)

-- 
2.39.5

[PATCH v4 1/3] Input: applespi - cancel pending work on driver remove

[Shih-Yuan Lee]

During driver removal in applespi_remove(), the managed private data
structure is freed by devres. However, the driver does not cancel the
asynchronous work applespi->work, which registers the touchpad input
device.

This creates a use-after-free (UAF) vulnerability if a pending or
running worker thread attempts to access the private data after the
remove function returns.

Fix this by explicitly calling cancel_work_sync(&applespi->work) in
applespi_remove() before cleanups.

Signed-off-by: Shih-Yuan Lee <fourdollars@debian.org>
---
 drivers/input/keyboard/applespi.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/input/keyboard/applespi.c b/drivers/input/keyboard/applespi.c
index b5ff71cd5a70..3bdb9e7cfb8b 100644
--- a/drivers/input/keyboard/applespi.c
+++ b/drivers/input/keyboard/applespi.c
@@ -1822,6 +1822,8 @@ static void applespi_remove(struct spi_device *spi)
 
 	applespi_drain_reads(applespi);
 
+	cancel_work_sync(&applespi->work);
+
 	debugfs_remove_recursive(applespi->debugfs_root);
 }
 
-- 
2.39.5

[PATCH v4 2/3] Input: applespi - fix NULL pointer dereference in tp_dim open

[Shih-Yuan Lee]

The tp_dim debugfs file is registered synchronously during driver probe
in applespi_probe(). However, the applespi->touchpad_input_dev is
initialized and registered asynchronously in the driver's worker thread.

If a userspace process opens the debugfs file before the worker thread
has completed initialization, applespi_tp_dim_open() will dereference
the NULL applespi->touchpad_input_dev pointer, causing a kernel panic.

Fix this by using smp_load_acquire() to safely load touchpad_input_dev
and return -ENODEV if it is not yet initialized.

Signed-off-by: Shih-Yuan Lee <fourdollars@debian.org>
---
 drivers/input/keyboard/applespi.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/input/keyboard/applespi.c b/drivers/input/keyboard/applespi.c
index 3bdb9e7cfb8b..4d339445e9c7 100644
--- a/drivers/input/keyboard/applespi.c
+++ b/drivers/input/keyboard/applespi.c
@@ -963,12 +963,18 @@ static void applespi_debug_update_dimensions(struct applespi_data *applespi,
 static int applespi_tp_dim_open(struct inode *inode, struct file *file)
 {
 	struct applespi_data *applespi = inode->i_private;
+	struct input_dev *touchpad;
 
 	file->private_data = applespi;
 
+	/* Pairs with smp_store_release in applespi_register_touchpad_device() */
+	touchpad = smp_load_acquire(&applespi->touchpad_input_dev);
+	if (!touchpad)
+		return -ENODEV;
+
 	snprintf(applespi->tp_dim_val, sizeof(applespi->tp_dim_val),
 		 "0x%.4x %dx%d+%u+%u\n",
-		 applespi->touchpad_input_dev->id.product,
+		 touchpad->id.product,
 		 applespi->tp_dim_min_x, applespi->tp_dim_min_y,
 		 applespi->tp_dim_max_x - applespi->tp_dim_min_x,
 		 applespi->tp_dim_max_y - applespi->tp_dim_min_y);
-- 
2.39.5

[PATCH v4 3/3] spi: pxa2xx: disable DMA for Apple MacBook8,1

[Shih-Yuan Lee]

On MacBook8,1 (early 2015 12" MacBook), the LPSS SPI controller's DMA
handshake and interrupt routing frequently fail or time out on boot,
causing the keyboard and trackpad to become unresponsive.

Avoid this architectural bug by disabling DMA and forcing the SPI
controller to use PIO mode. Move this platform/motherboard-level quirk
to the SPI host controller driver (spi-pxa2xx-pci.c) where LPSS setup
occurs, preventing layering violations, TOCTOU races, or execute-after-free
bugs in the client driver.

Additionally, introduce a `force_pio` module parameter in the PCI
host controller driver to allow other users to force PIO mode for
debugging.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=108331
Signed-off-by: Shih-Yuan Lee <fourdollars@debian.org>
---
 drivers/spi/spi-pxa2xx-pci.c | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-pxa2xx-pci.c b/drivers/spi/spi-pxa2xx-pci.c
index cae77ac18520..96bbc7a7c381 100644
--- a/drivers/spi/spi-pxa2xx-pci.c
+++ b/drivers/spi/spi-pxa2xx-pci.c
@@ -18,9 +18,14 @@
 
 #include <linux/dmaengine.h>
 #include <linux/platform_data/dma-dw.h>
+#include <linux/dmi.h>
 
 #include "spi-pxa2xx.h"
 
+static bool spi_pxa2xx_force_pio;
+module_param_named(force_pio, spi_pxa2xx_force_pio, bool, 0444);
+MODULE_PARM_DESC(force_pio, "Force PIO mode (disables DMA) for SPI transfers. ([0] = disabled, 1 = enabled)");
+
 #define PCI_DEVICE_ID_INTEL_QUARK_X1000		0x0935
 #define PCI_DEVICE_ID_INTEL_BYT			0x0f0e
 #define PCI_DEVICE_ID_INTEL_MRFLD		0x1194
@@ -93,6 +98,32 @@ static void lpss_dma_put_device(void *dma_dev)
 	pci_dev_put(dma_dev);
 }
 
+static const struct dmi_system_id pxa2xx_spi_pci_dmi_table[] = {
+	{
+		.ident = "Apple MacBook8,1",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "Apple Inc."),
+			DMI_MATCH(DMI_PRODUCT_NAME, "MacBook8,1"),
+		},
+	},
+	{ }
+};
+
+static bool pxa2xx_spi_pci_can_dma(struct pci_dev *dev)
+{
+	if (spi_pxa2xx_force_pio) {
+		pci_info(dev, "Forcing PIO mode (disabling DMA)\n");
+		return false;
+	}
+
+	if (dmi_check_system(pxa2xx_spi_pci_dmi_table)) {
+		pci_info(dev, "MacBook8,1 detected: disabling DMA to force PIO mode\n");
+		return false;
+	}
+
+	return true;
+}
+
 static int lpss_spi_setup(struct pci_dev *dev, struct pxa2xx_spi_controller *c)
 {
 	struct ssp_device *ssp = &c->ssp;
@@ -166,7 +197,7 @@ static int lpss_spi_setup(struct pci_dev *dev, struct pxa2xx_spi_controller *c)
 
 	c->dma_filter = lpss_dma_filter;
 	c->dma_burst_size = 1;
-	c->enable_dma = 1;
+	c->enable_dma = pxa2xx_spi_pci_can_dma(dev);
 	return 0;
 }
 
-- 
2.39.5