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

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Message-ID: <20230809144600.13721-1-kirill.shutemov@linux.intel.com>
Date:   Wed,  9 Aug 2023 17:46:00 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Kostya Serebryany <kcc@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Taras Madan <tarasmadan@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Christina Schimpe <christina.schimpe@...el.com>,
        stable@...r.kernel.org
Subject: [PATCH] mm: Fix access_remote_vm() regression on tagged addresses

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@...ux.intel.com>
Reported-by: Christina Schimpe <christina.schimpe@...el.com>
Fixes: eee9c708cc89 ("gup: avoid stack expansion warning for known-good case")
Cc: stable@...r.kernel.org
---
 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