From b71b55248a580e9c9befc4ae060539f1f8e477da Mon Sep 17 00:00:00 2001
From: Sudeep Holla <sudeep.holla@arm.com>
Date: Thu, 20 Apr 2023 16:06:01 +0100
Subject: [PATCH] firmware: arm_ffa: Check if ffa_driver remove is present before executing
Git-commit: b71b55248a580e9c9befc4ae060539f1f8e477da
Patch-mainline: v6.4-rc4
References: git-fixes

Currently ffa_drv->remove() is called unconditionally from
ffa_device_remove(). Since the driver registration doesn't check for it
and allows it to be registered without .remove callback, we need to check
for the presence of it before executing it from ffa_device_remove() to
above a NULL pointer dereference like the one below:

  | Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
  | Mem abort info:
  |   ESR = 0x0000000086000004
  |   EC = 0x21: IABT (current EL), IL = 32 bits
  |   SET = 0, FnV = 0
  |   EA = 0, S1PTW = 0
  |   FSC = 0x04: level 0 translation fault
  | user pgtable: 4k pages, 48-bit VAs, pgdp=0000000881cc8000
  | [0000000000000000] pgd=0000000000000000, p4d=0000000000000000
  | Internal error: Oops: 0000000086000004 [#1] PREEMPT SMP
  | CPU: 3 PID: 130 Comm: rmmod Not tainted 6.3.0-rc7 #6
  | Hardware name: FVP Base RevC (DT)
  | pstate: 63402809 (nZCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=-c)
  | pc : 0x0
  | lr : ffa_device_remove+0x20/0x2c
  | Call trace:
  |  0x0
  |  device_release_driver_internal+0x16c/0x260
  |  driver_detach+0x90/0xd0
  |  bus_remove_driver+0xdc/0x11c
  |  driver_unregister+0x30/0x54
  |  ffa_driver_unregister+0x14/0x20
  |  cleanup_module+0x18/0xeec
  |  __arm64_sys_delete_module+0x234/0x378
  |  invoke_syscall+0x40/0x108
  |  el0_svc_common+0xb4/0xf0
  |  do_el0_svc+0x30/0xa4
  |  el0_svc+0x2c/0x7c
  |  el0t_64_sync_handler+0x84/0xf0
  |  el0t_64_sync+0x190/0x194

Fixes: 244f5d597e1e ("firmware: arm_ffa: Add missing remove callback to ffa_bus_type")
Link: https://lore.kernel.org/r/20230419-ffa_fixes_6-4-v2-1-d9108e43a176@arm.com
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/firmware/arm_ffa/bus.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/firmware/arm_ffa/bus.c
+++ b/drivers/firmware/arm_ffa/bus.c
@@ -53,7 +53,8 @@ static void ffa_device_remove(struct dev
 {
 	struct ffa_driver *ffa_drv = to_ffa_driver(dev->driver);
 
-	ffa_drv->remove(to_ffa_dev(dev));
+	if (ffa_drv->remove)
+		ffa_drv->remove(to_ffa_dev(dev));
 }
 
 static int ffa_device_uevent(struct device *dev, struct kobj_uevent_env *env)