linux-kernel - [PATCH v5 4/4] lib/strn*,uaccess: Use masked_user_{read/write}_access

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Message-ID: <cb5e4b0fa49ea9c740570949d5e3544423389757.1763396724.git.christophe.leroy@csgroup.eu>
Date: Mon, 17 Nov 2025 17:43:44 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>,
	Ingo Molnar <mingo@...hat.com>,
	Darren Hart <dvhart@...radead.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	"Andre Almeida" <andrealmeid@...lia.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Kuniyuki Iwashima <kuniyu@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Willem de Bruijn <willemb@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>,
	Simon Horman <horms@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nichlas Piggin <npiggin@...il.com>,
	linux-block@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v5 4/4] lib/strn*,uaccess: Use masked_user_{read/write}_access_begin when required

Properly use masked_user_read_access_begin() and
masked_user_write_access_begin() instead of masked_user_access_begin()
in order to match user_read_access_end() and user_write_access_end().
This is important for architectures like powerpc that enable
separately user reads and user writes.

That means masked_user_read_access_begin() is used when user memory is
exclusively read during the window and masked_user_write_access_begin()
is used when user memory is exclusively writen during the window.
masked_user_access_begin() remains and is used when both reads and
writes are performed during the open window. Each of them is expected
to be terminated by the matching user_read_access_end(),
user_write_access_end() and user_access_end().

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
v5:
- Removed net/core/scm.c which is converted to scope user access by previous patch
- Renamed the patch as it now only handles lib/strncpy_from_user.c and lib/strnlen_user.c

v4: Rebased on top of core-scoped-uaccess tag

v3: Rebased on top of v6.18-rc1 ==> change in net/core/scm.c

v2: Added more explanations in the commit message following comments received.
---
 lib/strncpy_from_user.c | 2 +-
 lib/strnlen_user.c      | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
index 6dc234913dd5..5bb752ff7c61 100644
--- a/lib/strncpy_from_user.c
+++ b/lib/strncpy_from_user.c
@@ -126,7 +126,7 @@ long strncpy_from_user(char *dst, const char __user *src, long count)
 	if (can_do_masked_user_access()) {
 		long retval;
 
-		src = masked_user_access_begin(src);
+		src = masked_user_read_access_begin(src);
 		retval = do_strncpy_from_user(dst, src, count, count);
 		user_read_access_end();
 		return retval;
diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
index 6e489f9e90f1..4a6574b67f82 100644
--- a/lib/strnlen_user.c
+++ b/lib/strnlen_user.c
@@ -99,7 +99,7 @@ long strnlen_user(const char __user *str, long count)
 	if (can_do_masked_user_access()) {
 		long retval;
 
-		str = masked_user_access_begin(str);
+		str = masked_user_read_access_begin(str);
 		retval = do_strnlen_user(str, count, count);
 		user_read_access_end();
 		return retval;
-- 
2.49.0