fs/proc/kcore: convert read_kcore() to read_kcore_iter()

For the time being we still use a bounce buffer for vread(), however in
the next patch we will convert this to interact directly with the iterator
and eliminate the bounce buffer altogether.

Link: https://lkml.kernel.org/r/ebe12c8d70eebd71f487d80095605f3ad0d1489c.1679511146.git.lstoakes@gmail.comSigned-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Liu Shixin <liushixin2@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/proc/kcore.c

@@ -24,7 +24,7 @@
 #include <linux/memblock.h>
 #include <linux/init.h>
 #include <linux/slab.h>
-#include <linux/uaccess.h>
+#include <linux/uio.h>
 #include <asm/io.h>
 #include <linux/list.h>
 #include <linux/ioport.h>
@@ -308,9 +308,12 @@ static void append_kcore_note(char *notes, size_t *i, const char *name,
 }
 
 static ssize_t
-read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
+read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter)
 {
+	struct file *file = iocb->ki_filp;
 	char *buf = file->private_data;
+	loff_t *fpos = &iocb->ki_pos;
+
 	size_t phdrs_offset, notes_offset, data_offset;
 	size_t page_offline_frozen = 1;
 	size_t phdrs_len, notes_len;
@@ -318,6 +321,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 	size_t tsz;
 	int nphdr;
 	unsigned long start;
+	size_t buflen = iov_iter_count(iter);
 	size_t orig_buflen = buflen;
 	int ret = 0;
 
@@ -356,12 +360,11 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 		};
 
 		tsz = min_t(size_t, buflen, sizeof(struct elfhdr) - *fpos);
-		if (copy_to_user(buffer, (char *)&ehdr + *fpos, tsz)) {
+		if (copy_to_iter((char *)&ehdr + *fpos, tsz, iter) != tsz) {
 			ret = -EFAULT;
 			goto out;
 		}
 
-		buffer += tsz;
 		buflen -= tsz;
 		*fpos += tsz;
 	}
@@ -398,15 +401,14 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 		}
 
 		tsz = min_t(size_t, buflen, phdrs_offset + phdrs_len - *fpos);
-		if (copy_to_user(buffer, (char *)phdrs + *fpos - phdrs_offset,
-				 tsz)) {
+		if (copy_to_iter((char *)phdrs + *fpos - phdrs_offset, tsz,
+				 iter) != tsz) {
 			kfree(phdrs);
 			ret = -EFAULT;
 			goto out;
 		}
 		kfree(phdrs);
 
-		buffer += tsz;
 		buflen -= tsz;
 		*fpos += tsz;
 	}
@@ -448,14 +450,13 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 				  min(vmcoreinfo_size, notes_len - i));
 
 		tsz = min_t(size_t, buflen, notes_offset + notes_len - *fpos);
-		if (copy_to_user(buffer, notes + *fpos - notes_offset, tsz)) {
+		if (copy_to_iter(notes + *fpos - notes_offset, tsz, iter) != tsz) {
 			kfree(notes);
 			ret = -EFAULT;
 			goto out;
 		}
 		kfree(notes);
 
-		buffer += tsz;
 		buflen -= tsz;
 		*fpos += tsz;
 	}
@@ -497,7 +498,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 		}
 
 		if (!m) {
-			if (clear_user(buffer, tsz)) {
+			if (iov_iter_zero(tsz, iter) != tsz) {
 				ret = -EFAULT;
 				goto out;
 			}
@@ -508,14 +509,14 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 		case KCORE_VMALLOC:
 			vread(buf, (char *)start, tsz);
 			/* we have to zero-fill user buffer even if no read */
-			if (copy_to_user(buffer, buf, tsz)) {
+			if (copy_to_iter(buf, tsz, iter) != tsz) {
 				ret = -EFAULT;
 				goto out;
 			}
 			break;
 		case KCORE_USER:
 			/* User page is handled prior to normal kernel page: */
-			if (copy_to_user(buffer, (char *)start, tsz)) {
+			if (copy_to_iter((char *)start, tsz, iter) != tsz) {
 				ret = -EFAULT;
 				goto out;
 			}
@@ -531,7 +532,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 			 */
 			if (!page || PageOffline(page) ||
 			    is_page_hwpoison(page) || !pfn_is_ram(pfn)) {
-				if (clear_user(buffer, tsz)) {
+				if (iov_iter_zero(tsz, iter) != tsz) {
 					ret = -EFAULT;
 					goto out;
 				}
@@ -541,17 +542,17 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 		case KCORE_VMEMMAP:
 		case KCORE_TEXT:
 			/*
-			 * We use _copy_to_user() to bypass usermode hardening
+			 * We use _copy_to_iter() to bypass usermode hardening
 			 * which would otherwise prevent this operation.
 			 */
-			if (_copy_to_user(buffer, (char *)start, tsz)) {
+			if (_copy_to_iter((char *)start, tsz, iter) != tsz) {
 				ret = -EFAULT;
 				goto out;
 			}
 			break;
 		default:
 			pr_warn_once("Unhandled KCORE type: %d\n", m->type);
-			if (clear_user(buffer, tsz)) {
+			if (iov_iter_zero(tsz, iter) != tsz) {
 				ret = -EFAULT;
 				goto out;
 			}
@@ -559,7 +560,6 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 skip:
 		buflen -= tsz;
 		*fpos += tsz;
-		buffer += tsz;
 		start += tsz;
 		tsz = (buflen > PAGE_SIZE ? PAGE_SIZE : buflen);
 	}
@@ -603,7 +603,7 @@ static int release_kcore(struct inode *inode, struct file *file)
 }
 
 static const struct proc_ops kcore_proc_ops = {
-	.proc_read	= read_kcore,
+	.proc_read_iter	= read_kcore_iter,
 	.proc_open	= open_kcore,
 	.proc_release	= release_kcore,
 	.proc_lseek	= default_llseek,