[PATCH] mm: Fix access_remote_vm() regression on tagged addresses

[Kirill A. Shutemov]

GDB uses /proc/PID/mem to access memory of the target process. GDB
doesn't untag addresses manually, but relies on kernel to do the right
thing.

mem_rw() of procfs uses access_remote_vm() to get data from the target
process. It worked fine until recent changes in __access_remote_vm()
that now checks if there's VMA at target address using raw address.

Untag the address before looking up the VMA.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reported-by: Christina Schimpe <christina.schimpe@xxxxxxxxx>
Fixes: eee9c708cc89 ("gup: avoid stack expansion warning for known-good case")
Cc: stable@xxxxxxxxxxxxxxx
---
 mm/memory.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index 01f39e8144ef..3be9db30db32 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5701,6 +5701,9 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
 	if (mmap_read_lock_killable(mm))
 		return 0;
 
+	/* Untag the address before looking up the VMA */
+	addr = untagged_addr_remote(mm, addr);
+
 	/* Avoid triggering the temporary warning in __get_user_pages */
 	if (!vma_lookup(mm, addr) && !expand_stack(mm, addr))
 		return 0;
-- 
2.41.0