linux-kernel - [PATCH v2 04/10] powerpc/uaccess: Move barrier_nospec() out of allow_read_{from/write}

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Message-ID: <90ce0c90c53d3132023d753650b1741fab60dcd3.1755854833.git.christophe.leroy@csgroup.eu>
Date: Fri, 22 Aug 2025 11:58:00 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Darren Hart <dvhart@...radead.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	"Andre Almeida" <andrealmeid@...lia.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Laight <david.laight.linux@...il.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Daniel Borkmann <daniel@...earbox.net>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-block@...r.kernel.org
Subject: [PATCH v2 04/10] powerpc/uaccess: Move barrier_nospec() out of allow_read_{from/write}_user()

Commit 74e19ef0ff80 ("uaccess: Add speculation barrier to
copy_from_user()") added a redundant barrier_nospec() in
copy_from_user(), because powerpc is already calling
barrier_nospec() in allow_read_from_user() and
allow_read_write_user(). But on other architectures that
call to barrier_nospec() was missing. So change powerpc
instead of reverting the above commit and having to fix
other architectures one by one. This is now possible
because barrier_nospec() has also been added in
copy_from_user_iter().

Move barrier_nospec() out of allow_read_from_user() and
allow_read_write_user(). This will also allow reuse of those
functions when implementing masked user access which doesn't
require barrier_nospec().

Don't add it back in raw_copy_from_user() as it is already called
by copy_from_user() and copy_from_user_iter().

Fixes: 74e19ef0ff80 ("uaccess: Add speculation barrier to copy_from_user()")
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/include/asm/kup.h     | 2 --
 arch/powerpc/include/asm/uaccess.h | 4 ++++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index 2bb03d941e3e..6737416dde9f 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -134,7 +134,6 @@ static __always_inline void kuap_assert_locked(void)
 
 static __always_inline void allow_read_from_user(const void __user *from, unsigned long size)
 {
-	barrier_nospec();
 	allow_user_access(NULL, from, size, KUAP_READ);
 }
 
@@ -146,7 +145,6 @@ static __always_inline void allow_write_to_user(void __user *to, unsigned long s
 static __always_inline void allow_read_write_user(void __user *to, const void __user *from,
 						  unsigned long size)
 {
-	barrier_nospec();
 	allow_user_access(to, from, size, KUAP_READ_WRITE);
 }
 
diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 4f5a46a77fa2..3987a5c33558 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -301,6 +301,7 @@ do {								\
 	__typeof__(sizeof(*(ptr))) __gu_size = sizeof(*(ptr));	\
 								\
 	might_fault();					\
+	barrier_nospec();					\
 	allow_read_from_user(__gu_addr, __gu_size);		\
 	__get_user_size_allowed(__gu_val, __gu_addr, __gu_size, __gu_err);	\
 	prevent_read_from_user(__gu_addr, __gu_size);		\
@@ -329,6 +330,7 @@ raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
 {
 	unsigned long ret;
 
+	barrier_nospec();
 	allow_read_write_user(to, from, n);
 	ret = __copy_tofrom_user(to, from, n);
 	prevent_read_write_user(to, from, n);
@@ -415,6 +417,7 @@ static __must_check __always_inline bool user_access_begin(const void __user *pt
 
 	might_fault();
 
+	barrier_nospec();
 	allow_read_write_user((void __user *)ptr, ptr, len);
 	return true;
 }
@@ -431,6 +434,7 @@ user_read_access_begin(const void __user *ptr, size_t len)
 
 	might_fault();
 
+	barrier_nospec();
 	allow_read_from_user(ptr, len);
 	return true;
 }
-- 
2.49.0