Re: [RFC PATCH 01/14] fs/proc/vmcore: Update read_from_oldmem() for user pointer

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On 12/6/21 7:34 PM, Christoph Hellwig wrote:
On Fri, Dec 03, 2021 at 04:12:18PM +0530, Amit Daniel Kachhap wrote:
+	return read_from_oldmem_to_kernel(buf, count, ppos,
+					  cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT));

Overly long line.

+ssize_t read_from_oldmem(char __user *ubuf, char *kbuf, size_t count,
+			 u64 *ppos, bool encrypted)
  {
  	unsigned long pfn, offset;
  	size_t nr_bytes;
@@ -156,19 +163,27 @@ ssize_t read_from_oldmem(char *buf, size_t count,
  		/* If pfn is not ram, return zeros for sparse dump files */
  		if (!pfn_is_ram(pfn)) {
  			tmp = 0;
-			if (!userbuf)
-				memset(buf, 0, nr_bytes);
-			else if (clear_user(buf, nr_bytes))
+			if (kbuf)
+				memset(kbuf, 0, nr_bytes);
+			else if (clear_user(ubuf, nr_bytes))
  				tmp = -EFAULT;

This looks like a huge mess.  What speak against using an iov_iter
here?

iov_iter seems to be a reasonable way. As a start I thought of adding
minimal changes.



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