pstore/pmsg: drop bounce buffer

Removing a bounce buffer copy operation in the pmsg driver path is
always better. We also gain in overall performance by not requesting
a vmalloc on every write as this can cause precious RT tasks, such
as user facing media operation, to stall while memory is being
reclaimed. Added a write_buf_user to the pstore functions, a backup
platform write_buf_user that uses the small buffer that is part of
the instance, and implemented a ramoops write_buf_user that only
supports PSTORE_TYPE_PMSG.
Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

fs/pstore/platform.c

@@ -623,6 +623,40 @@ static int pstore_write_compat(enum pstore_type_id type,
 			     size, psi);
 }
 
+static int pstore_write_buf_user_compat(enum pstore_type_id type,
+			       enum kmsg_dump_reason reason,
+			       u64 *id, unsigned int part,
+			       const char __user *buf,
+			       bool compressed, size_t size,
+			       struct pstore_info *psi)
+{
+	unsigned long flags = 0;
+	size_t i, bufsize = size;
+	long ret = 0;
+
+	if (unlikely(!access_ok(VERIFY_READ, buf, size)))
+		return -EFAULT;
+	if (bufsize > psinfo->bufsize)
+		bufsize = psinfo->bufsize;
+	spin_lock_irqsave(&psinfo->buf_lock, flags);
+	for (i = 0; i < size; ) {
+		size_t c = min(size - i, bufsize);
+
+		ret = __copy_from_user(psinfo->buf, buf + i, c);
+		if (unlikely(ret != 0)) {
+			ret = -EFAULT;
+			break;
+		}
+		ret = psi->write_buf(type, reason, id, part, psinfo->buf,
+				     compressed, c, psi);
+		if (unlikely(ret < 0))
+			break;
+		i += c;
+	}
+	spin_unlock_irqrestore(&psinfo->buf_lock, flags);
+	return unlikely(ret < 0) ? ret : size;
+}
+
 /*
  * platform specific persistent storage driver registers with
  * us here. If pstore is already mounted, call the platform
@@ -645,6 +679,8 @@ int pstore_register(struct pstore_info *psi)
 
 	if (!psi->write)
 		psi->write = pstore_write_compat;
+	if (!psi->write_buf_user)
+		psi->write_buf_user = pstore_write_buf_user_compat;
 	psinfo = psi;
 	mutex_init(&psinfo->read_mutex);
 	spin_unlock(&pstore_lock);

fs/pstore/pmsg.c

@@ -19,48 +19,25 @@
 #include "internal.h"
 
 static DEFINE_MUTEX(pmsg_lock);
-#define PMSG_MAX_BOUNCE_BUFFER_SIZE (2*PAGE_SIZE)
 
 static ssize_t write_pmsg(struct file *file, const char __user *buf,
 			  size_t count, loff_t *ppos)
 {
-	size_t i, buffer_size;
-	char *buffer;
+	u64 id;
+	int ret;
 
 	if (!count)
 		return 0;
 
+	/* check outside lock, page in any data. write_buf_user also checks */
 	if (!access_ok(VERIFY_READ, buf, count))
 		return -EFAULT;
 
-	buffer_size = count;
-	if (buffer_size > PMSG_MAX_BOUNCE_BUFFER_SIZE)
-		buffer_size = PMSG_MAX_BOUNCE_BUFFER_SIZE;
-	buffer = vmalloc(buffer_size);
-	if (!buffer)
-		return -ENOMEM;
-
 	mutex_lock(&pmsg_lock);
-	for (i = 0; i < count; ) {
-		size_t c = min(count - i, buffer_size);
-		u64 id;
-		long ret;
-
-		ret = __copy_from_user(buffer, buf + i, c);
-		if (unlikely(ret != 0)) {
-			mutex_unlock(&pmsg_lock);
-			vfree(buffer);
-			return -EFAULT;
-		}
-		psinfo->write_buf(PSTORE_TYPE_PMSG, 0, &id, 0, buffer, 0, c,
+	ret = psinfo->write_buf_user(PSTORE_TYPE_PMSG, 0, &id, 0, buf, 0, count,
 				     psinfo);
-
-		i += c;
-	}
-
 	mutex_unlock(&pmsg_lock);
-	vfree(buffer);
-	return count;
+	return ret ? ret : count;
 }
 
 static const struct file_operations pmsg_fops = {

fs/pstore/ram.c

@@ -331,6 +331,24 @@ static int notrace ramoops_pstore_write_buf(enum pstore_type_id type,
 	return 0;
 }
 
+static int notrace ramoops_pstore_write_buf_user(enum pstore_type_id type,
+						 enum kmsg_dump_reason reason,
+						 u64 *id, unsigned int part,
+						 const char __user *buf,
+						 bool compressed, size_t size,
+						 struct pstore_info *psi)
+{
+	if (type == PSTORE_TYPE_PMSG) {
+		struct ramoops_context *cxt = psi->data;
+
+		if (!cxt->mprz)
+			return -ENOMEM;
+		return persistent_ram_write_user(cxt->mprz, buf, size);
+	}
+
+	return -EINVAL;
+}
+
 static int ramoops_pstore_erase(enum pstore_type_id type, u64 id, int count,
 				struct timespec time, struct pstore_info *psi)
 {
@@ -369,6 +387,7 @@ static struct ramoops_context oops_cxt = {
 		.open	= ramoops_pstore_open,
 		.read	= ramoops_pstore_read,
 		.write_buf	= ramoops_pstore_write_buf,
+		.write_buf_user	= ramoops_pstore_write_buf_user,
 		.erase	= ramoops_pstore_erase,
 	},
 };

fs/pstore/ram_core.c

@@ -17,15 +17,16 @@
 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/errno.h>
-#include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/io.h>
+#include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/memblock.h>
+#include <linux/pstore_ram.h>
 #include <linux/rslib.h>
 #include <linux/slab.h>
+#include <linux/uaccess.h>
 #include <linux/vmalloc.h>
-#include <linux/pstore_ram.h>
 #include <asm/page.h>
 
 struct persistent_ram_buffer {
@@ -267,6 +268,16 @@ static void notrace persistent_ram_update(struct persistent_ram_zone *prz,
 	persistent_ram_update_ecc(prz, start, count);
 }
 
+static int notrace persistent_ram_update_user(struct persistent_ram_zone *prz,
+	const void __user *s, unsigned int start, unsigned int count)
+{
+	struct persistent_ram_buffer *buffer = prz->buffer;
+	int ret = unlikely(__copy_from_user(buffer->data + start, s, count)) ?
+		-EFAULT : 0;
+	persistent_ram_update_ecc(prz, start, count);
+	return ret;
+}
+
 void persistent_ram_save_old(struct persistent_ram_zone *prz)
 {
 	struct persistent_ram_buffer *buffer = prz->buffer;
@@ -320,6 +331,38 @@ int notrace persistent_ram_write(struct persistent_ram_zone *prz,
 	return count;
 }
 
+int notrace persistent_ram_write_user(struct persistent_ram_zone *prz,
+	const void __user *s, unsigned int count)
+{
+	int rem, ret = 0, c = count;
+	size_t start;
+
+	if (unlikely(!access_ok(VERIFY_READ, s, count)))
+		return -EFAULT;
+	if (unlikely(c > prz->buffer_size)) {
+		s += c - prz->buffer_size;
+		c = prz->buffer_size;
+	}
+
+	buffer_size_add(prz, c);
+
+	start = buffer_start_add(prz, c);
+
+	rem = prz->buffer_size - start;
+	if (unlikely(rem < c)) {
+		ret = persistent_ram_update_user(prz, s, start, rem);
+		s += rem;
+		c -= rem;
+		start = 0;
+	}
+	if (likely(!ret))
+		ret = persistent_ram_update_user(prz, s, start, c);
+
+	persistent_ram_update_header_ecc(prz);
+
+	return unlikely(ret) ? ret : count;
+}
+
 size_t persistent_ram_old_size(struct persistent_ram_zone *prz)
 {
 	return prz->old_log_size;

include/linux/pstore.h

@@ -22,12 +22,13 @@
 #ifndef _LINUX_PSTORE_H
 #define _LINUX_PSTORE_H
 
-#include <linux/time.h>
+#include <linux/compiler.h>
+#include <linux/errno.h>
 #include <linux/kmsg_dump.h>
 #include <linux/mutex.h>
-#include <linux/types.h>
 #include <linux/spinlock.h>
-#include <linux/errno.h>
+#include <linux/time.h>
+#include <linux/types.h>
 
 /* types */
 enum pstore_type_id {
@@ -68,6 +69,10 @@ struct pstore_info {
 			enum kmsg_dump_reason reason, u64 *id,
 			unsigned int part, const char *buf, bool compressed,
 			size_t size, struct pstore_info *psi);
+	int		(*write_buf_user)(enum pstore_type_id type,
+			enum kmsg_dump_reason reason, u64 *id,
+			unsigned int part, const char __user *buf,
+			bool compressed, size_t size, struct pstore_info *psi);
 	int		(*erase)(enum pstore_type_id type, u64 id,
 			int count, struct timespec time,
 			struct pstore_info *psi);

include/linux/pstore_ram.h

@@ -17,11 +17,12 @@
 #ifndef __LINUX_PSTORE_RAM_H__
 #define __LINUX_PSTORE_RAM_H__
 
+#include <linux/compiler.h>
 #include <linux/device.h>
+#include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/types.h>
-#include <linux/init.h>
 
 struct persistent_ram_buffer;
 struct rs_control;
@@ -60,6 +61,8 @@ void persistent_ram_zap(struct persistent_ram_zone *prz);
 
 int persistent_ram_write(struct persistent_ram_zone *prz, const void *s,
 			 unsigned int count);
+int persistent_ram_write_user(struct persistent_ram_zone *prz,
+			      const void __user *s, unsigned int count);
 
 void persistent_ram_save_old(struct persistent_ram_zone *prz);
 size_t persistent_ram_old_size(struct persistent_ram_zone *prz);