drm/msm: Add a way to override processes comm/cmdline

In the cause of using the GPU via virtgpu, the host side process is
really a sort of proxy, and not terribly interesting from the PoV of
crash/fault logging.  Add a way to override these per process so that
we can see the guest process's name.

v2: Handle kmalloc failure, add comment to explain kstrdup returns
    NULL if passed NULL [Dan Carpenter]
Signed-off-by: Rob Clark <robdclark@chromium.org>
Link: https://lore.kernel.org/r/20220317165144.222101-4-robdclark@gmail.comSigned-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/adreno/adreno_gpu.c

@@ -290,11 +290,48 @@ int adreno_get_param(struct msm_gpu *gpu, struct msm_file_private *ctx,
 int adreno_set_param(struct msm_gpu *gpu, struct msm_file_private *ctx,
 		     uint32_t param, uint64_t value, uint32_t len)
 {
-	/* No pointer params yet */
-	if (len != 0)
-		return -EINVAL;
+	switch (param) {
+	case MSM_PARAM_COMM:
+	case MSM_PARAM_CMDLINE:
+		/* kstrdup_quotable_cmdline() limits to PAGE_SIZE, so
+		 * that should be a reasonable upper bound
+		 */
+		if (len > PAGE_SIZE)
+			return -EINVAL;
+		break;
+	default:
+		if (len != 0)
+			return -EINVAL;
+	}
 
 	switch (param) {
+	case MSM_PARAM_COMM:
+	case MSM_PARAM_CMDLINE: {
+		char *str, **paramp;
+
+		str = kmalloc(len + 1, GFP_KERNEL);
+		if (!str)
+			return -ENOMEM;
+
+		if (copy_from_user(str, u64_to_user_ptr(value), len)) {
+			kfree(str);
+			return -EFAULT;
+		}
+
+		/* Ensure string is null terminated: */
+		str[len] = '\0';
+
+		if (param == MSM_PARAM_COMM) {
+			paramp = &ctx->comm;
+		} else {
+			paramp = &ctx->cmdline;
+		}
+
+		kfree(*paramp);
+		*paramp = str;
+
+		return 0;
+	}
 	case MSM_PARAM_SYSPROF:
 		if (!capable(CAP_SYS_ADMIN))
 			return -EPERM;

drivers/gpu/drm/msm/msm_gpu.c

@@ -353,14 +353,22 @@ static void retire_submits(struct msm_gpu *gpu);
 
 static void get_comm_cmdline(struct msm_gem_submit *submit, char **comm, char **cmd)
 {
+	struct msm_file_private *ctx = submit->queue->ctx;
 	struct task_struct *task;
 
+	/* Note that kstrdup will return NULL if argument is NULL: */
+	*comm = kstrdup(ctx->comm, GFP_KERNEL);
+	*cmd  = kstrdup(ctx->cmdline, GFP_KERNEL);
+
 	task = get_pid_task(submit->pid, PIDTYPE_PID);
 	if (!task)
 		return;
 
-	*comm = kstrdup(task->comm, GFP_KERNEL);
-	*cmd = kstrdup_quotable_cmdline(task, GFP_KERNEL);
+	if (!*comm)
+		*comm = kstrdup(task->comm, GFP_KERNEL);
+
+	if (!*cmd)
+		*cmd = kstrdup_quotable_cmdline(task, GFP_KERNEL);
 
 	put_task_struct(task);
 }

drivers/gpu/drm/msm/msm_gpu.h

@@ -355,6 +355,12 @@ struct msm_file_private {
 	 */
 	int sysprof;
 
+	/** comm: Overridden task comm, see MSM_PARAM_COMM */
+	char *comm;
+
+	/** cmdline: Overridden task cmdline, see MSM_PARAM_CMDLINE */
+	char *cmdline;
+
 	/**
 	 * entities:
 	 *

drivers/gpu/drm/msm/msm_submitqueue.c

@@ -61,6 +61,8 @@ void __msm_file_private_destroy(struct kref *kref)
 	}
 
 	msm_gem_address_space_put(ctx->aspace);
+	kfree(ctx->comm);
+	kfree(ctx->cmdline);
 	kfree(ctx);
 }
 

include/uapi/drm/msm_drm.h

@@ -82,6 +82,8 @@ struct drm_msm_timespec {
 #define MSM_PARAM_FAULTS     0x09  /* RO */
 #define MSM_PARAM_SUSPENDS   0x0a  /* RO */
 #define MSM_PARAM_SYSPROF    0x0b  /* WO: 1 preserves perfcntrs, 2 also disables suspend */
+#define MSM_PARAM_COMM       0x0c  /* WO: override for task->comm */
+#define MSM_PARAM_CMDLINE    0x0d  /* WO: override for task cmdline */
 
 /* For backwards compat.  The original support for preemption was based on
  * a single ring per priority level so # of priority levels equals the #