linux-kernel - [PATCH 2/2] fs: Use masked_user_read_access

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Message-Id: <20250209105600.3388-3-david.laight.linux@gmail.com>
Date: Sun,  9 Feb 2025 10:56:00 +0000
From: David Laight <david.laight.linux@...il.com>
To: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc: David Laight <david.laight.linux@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>,
	Arnd Bergmann <arnd@...db.de>,
	Kees Cook <kees@...nel.org>
Subject: [PATCH 2/2] fs: Use masked_user_read_access_begin()

Commit 2865baf54077a changed get_sigset_argpack() to use
masked_user_access_begin() and avoid a slow synchronisation instruction.

Replace the rather unwieldy code pattern with
masked_user_read_access_begin().
Make the same change to get_compat_sigset_argpack().

Use masked_user_write_access_begin() in do_sys_poll() to avoid
the size calculation and conditional branch for access_ok().

Code generated for get_sigset_argpack() is identical.

Signed-off-by: David Laight <david.laight.linux@...il.com>
---
 fs/select.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/fs/select.c b/fs/select.c
index 7da531b1cf6b..abe2c1a57274 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -776,9 +776,7 @@ static inline int get_sigset_argpack(struct sigset_argpack *to,
 {
 	// the path is hot enough for overhead of copy_from_user() to matter
 	if (from) {
-		if (can_do_masked_user_access())
-			from = masked_user_access_begin(from);
-		else if (!user_read_access_begin(from, sizeof(*from)))
+		if (!masked_user_read_access_begin(&from, sizeof(*from)))
 			return -EFAULT;
 		unsafe_get_user(to->p, &from->p, Efault);
 		unsafe_get_user(to->size, &from->size, Efault);
@@ -1009,7 +1007,7 @@ static int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds,
 	fdcount = do_poll(head, &table, end_time);
 	poll_freewait(&table);
 
-	if (!user_write_access_begin(ufds, nfds * sizeof(*ufds)))
+	if (!masked_user_write_access_begin(&ufds, nfds * sizeof(*ufds)))
 		goto out_fds;
 
 	for (walk = head; walk; walk = walk->next) {
@@ -1347,7 +1345,7 @@ static inline int get_compat_sigset_argpack(struct compat_sigset_argpack *to,
 					    struct compat_sigset_argpack __user *from)
 {
 	if (from) {
-		if (!user_read_access_begin(from, sizeof(*from)))
+		if (!masked_user_read_access_begin(&from, sizeof(*from)))
 			return -EFAULT;
 		unsafe_get_user(to->p, &from->p, Efault);
 		unsafe_get_user(to->size, &from->size, Efault);
-- 
2.39.5