drm/amdgpu/pm: Remove VLA usage

In the quest to remove all stack VLA usage from the kernel[1], this
uses the maximum sane buffer size and removes copy/paste code.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Reviewed-by: Rex Zhu <rezhu@amd.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c

@@ -606,40 +606,59 @@ static ssize_t amdgpu_get_pp_dpm_sclk(struct device *dev,
 		return snprintf(buf, PAGE_SIZE, "\n");
 }
 
-static ssize_t amdgpu_set_pp_dpm_sclk(struct device *dev,
-		struct device_attribute *attr,
-		const char *buf,
-		size_t count)
+/*
+ * Worst case: 32 bits individually specified, in octal at 12 characters
+ * per line (+1 for \n).
+ */
+#define AMDGPU_MASK_BUF_MAX	(32 * 13)
+
+static ssize_t amdgpu_read_mask(const char *buf, size_t count, uint32_t *mask)
 {
-	struct drm_device *ddev = dev_get_drvdata(dev);
-	struct amdgpu_device *adev = ddev->dev_private;
 	int ret;
 	long level;
-	uint32_t mask = 0;
 	char *sub_str = NULL;
 	char *tmp;
-	char buf_cpy[count];
+	char buf_cpy[AMDGPU_MASK_BUF_MAX + 1];
 	const char delimiter[3] = {' ', '\n', '\0'};
+	size_t bytes;
 
-	memcpy(buf_cpy, buf, count+1);
+	*mask = 0;
+
+	bytes = min(count, sizeof(buf_cpy) - 1);
+	memcpy(buf_cpy, buf, bytes);
+	buf_cpy[bytes] = '\0';
 	tmp = buf_cpy;
 	while (tmp[0]) {
-		sub_str =  strsep(&tmp, delimiter);
+		sub_str = strsep(&tmp, delimiter);
 		if (strlen(sub_str)) {
 			ret = kstrtol(sub_str, 0, &level);
-
-			if (ret) {
-				count = -EINVAL;
-				goto fail;
-			}
-			mask |= 1 << level;
+			if (ret)
+				return -EINVAL;
+			*mask |= 1 << level;
 		} else
 			break;
 	}
+
+	return 0;
+}
+
+static ssize_t amdgpu_set_pp_dpm_sclk(struct device *dev,
+		struct device_attribute *attr,
+		const char *buf,
+		size_t count)
+{
+	struct drm_device *ddev = dev_get_drvdata(dev);
+	struct amdgpu_device *adev = ddev->dev_private;
+	int ret;
+	uint32_t mask = 0;
+
+	ret = amdgpu_read_mask(buf, count, &mask);
+	if (ret)
+		return ret;
+
 	if (adev->powerplay.pp_funcs->force_clock_level)
 		amdgpu_dpm_force_clock_level(adev, PP_SCLK, mask);
 
-fail:
 	return count;
 }
 
@@ -664,32 +683,15 @@ static ssize_t amdgpu_set_pp_dpm_mclk(struct device *dev,
 	struct drm_device *ddev = dev_get_drvdata(dev);
 	struct amdgpu_device *adev = ddev->dev_private;
 	int ret;
-	long level;
 	uint32_t mask = 0;
-	char *sub_str = NULL;
-	char *tmp;
-	char buf_cpy[count];
-	const char delimiter[3] = {' ', '\n', '\0'};
 
-	memcpy(buf_cpy, buf, count+1);
-	tmp = buf_cpy;
-	while (tmp[0]) {
-		sub_str =  strsep(&tmp, delimiter);
-		if (strlen(sub_str)) {
-			ret = kstrtol(sub_str, 0, &level);
+	ret = amdgpu_read_mask(buf, count, &mask);
+	if (ret)
+		return ret;
 
-			if (ret) {
-				count = -EINVAL;
-				goto fail;
-			}
-			mask |= 1 << level;
-		} else
-			break;
-	}
 	if (adev->powerplay.pp_funcs->force_clock_level)
 		amdgpu_dpm_force_clock_level(adev, PP_MCLK, mask);
 
-fail:
 	return count;
 }
 
@@ -714,33 +716,15 @@ static ssize_t amdgpu_set_pp_dpm_pcie(struct device *dev,
 	struct drm_device *ddev = dev_get_drvdata(dev);
 	struct amdgpu_device *adev = ddev->dev_private;
 	int ret;
-	long level;
 	uint32_t mask = 0;
-	char *sub_str = NULL;
-	char *tmp;
-	char buf_cpy[count];
-	const char delimiter[3] = {' ', '\n', '\0'};
-
-	memcpy(buf_cpy, buf, count+1);
-	tmp = buf_cpy;
 
-	while (tmp[0]) {
-		sub_str =  strsep(&tmp, delimiter);
-		if (strlen(sub_str)) {
-			ret = kstrtol(sub_str, 0, &level);
+	ret = amdgpu_read_mask(buf, count, &mask);
+	if (ret)
+		return ret;
 
-			if (ret) {
-				count = -EINVAL;
-				goto fail;
-			}
-			mask |= 1 << level;
-		} else
-			break;
-	}
 	if (adev->powerplay.pp_funcs->force_clock_level)
 		amdgpu_dpm_force_clock_level(adev, PP_PCIE, mask);
 
-fail:
 	return count;
 }