linux-kernel - [PATCH v5 1/4] iov_iter: Convert copy_from_user

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Message-ID: <58e4b07d469ca68a2b9477fe2c1ccc8a44cef131.1763396724.git.christophe.leroy@csgroup.eu>
Date: Mon, 17 Nov 2025 17:43:41 +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 1/4] iov_iter: Convert copy_from_user_iter() to masked user access

Following patch will add missing barrier_nospec() to
copy_from_user_iter(). On some architecture like x86 it might
degrade performance, which would be unfortunate as
copy_from_user_iter() is a critical function.

Convert copy_from_user_iter() to using masked user access on
architecture that support it.

This is similar to what was done for copy_from_user() by
commit 0fc810ae3ae1 ("x86/uaccess: Avoid barrier_nospec()
in 64-bit copy_from_user()")

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
v5: Changed commit message

v2: New in v2
---
 lib/iov_iter.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 2fe66a6b8789..a589935bf302 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -49,12 +49,16 @@ size_t copy_from_user_iter(void __user *iter_from, size_t progress,
 
 	if (should_fail_usercopy())
 		return len;
-	if (access_ok(iter_from, len)) {
-		to += progress;
-		instrument_copy_from_user_before(to, iter_from, len);
-		res = raw_copy_from_user(to, iter_from, len);
-		instrument_copy_from_user_after(to, iter_from, len, res);
-	}
+	if (can_do_masked_user_access())
+		iter_from = mask_user_address(iter_from);
+	else if (!access_ok(iter_from, len))
+		return res;
+
+	to += progress;
+	instrument_copy_from_user_before(to, iter_from, len);
+	res = raw_copy_from_user(to, iter_from, len);
+	instrument_copy_from_user_after(to, iter_from, len, res);
+
 	return res;
 }
 
-- 
2.49.0