linux-kernel - [PATCH v3 2/3] mm/gup: remove unneeded checking in follow_page

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250407030306.411977-3-bhe@redhat.com>
Date: Mon,  7 Apr 2025 11:03:05 +0800
From: Baoquan He <bhe@...hat.com>
To: linux-mm@...ck.org
Cc: akpm@...ux-foundation.org,
	osalvador@...e.de,
	david@...hat.com,
	mingo@...nel.org,
	yanjun.zhu@...ux.dev,
	linux-kernel@...r.kernel.org,
	Baoquan He <bhe@...hat.com>
Subject: [PATCH v3 2/3] mm/gup: remove unneeded checking in follow_page_pte()

In __get_user_pages(), it will traverse page table and take a reference
to the page the given user address corresponds to if GUP_GET or GUP_PIN
is set. However, it's not supported both GUP_GET and GUP_PIN are set.
Even though this check need be done, it should be done earlier, but not
doing it till entering into follow_page_pte() and failed.

Furthermore, this checking has been done in is_valid_gup_args() and all
external users of __get_user_pages() will call is_valid_gup_args() to
catch the illegal setting. We don't need to worry about internal users
of __get_user_pages() because the gup_flags are set by MM code correctly.

Here remove the checking in follow_page_pte(), and add VM_WARN_ON_ONCE()
to catch the possible exceptional setting just in case.

And also change the VM_BUG_ON to VM_WARN_ON_ONCE() for checking
(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN))) because the checking
has been done in is_valid_gup_args() for external users of __get_user_pages().

Signed-off-by: Baoquan He <bhe@...hat.com>
---
 mm/gup.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 67a7de9e4f80..5b3ac5a867a3 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -844,11 +844,6 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
 	pte_t *ptep, pte;
 	int ret;

-	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
-	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
-			 (FOLL_PIN | FOLL_GET)))
-		return ERR_PTR(-EINVAL);
-
 	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
 	if (!ptep)
 		return no_page_table(vma, flags, address);
@@ -1432,7 +1427,11 @@ static long __get_user_pages(struct mm_struct *mm,

 	start = untagged_addr_remote(mm, start);

-	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
+	VM_WARN_ON_ONCE(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
+
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	VM_WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
+			(FOLL_PIN | FOLL_GET));

 	do {
 		struct page *page;
-- 
2.41.0