linux-kernel - [PATCH v2] xtensa: align: validate access in fast_load

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Message-ID: <20251214222856.2714887-2-richard.rringler@gmail.com>
Date: Sun, 14 Dec 2025 16:28:57 -0600
From: Ricky Ringler <richard.rringler@...il.com>
To: Max Filippov <jcmvbkbc@...il.com>,
	Chris Zankel <chris@...kel.net>
Cc: linux-kernel@...r.kernel.org,
	Ricky Ringler <richard.rringler@...il.com>
Subject: [PATCH v2] xtensa: align: validate access in fast_load_store

access_ok() is used only in user mode and
branches to .Linvalid_instruction on fault.
Kernel mode behavior unchanged.

v2:
- Address Max's feedback
- Fixed formatting
- Added user mode branch

Tested-by: Ricky Ringler <richard.rringler@...il.com>

Testing:
- Built with CONFIG_MMU enabled
- objdump before/after comparison and validated code path

Signed-off-by: Ricky Ringler <richard.rringler@...il.com>
---
 arch/xtensa/kernel/align.S | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/xtensa/kernel/align.S b/arch/xtensa/kernel/align.S
index ee97edce2300..64e775933e9b 100644
--- a/arch/xtensa/kernel/align.S
+++ b/arch/xtensa/kernel/align.S
@@ -21,6 +21,9 @@
 #include <asm/asm-offsets.h>
 #include <asm/asmmacro.h>
 #include <asm/processor.h>
+#ifdef CONFIG_MMU
+#include <asm/asm-uaccess.h>
+#endif
 
 #if XCHAL_UNALIGNED_LOAD_EXCEPTION || defined CONFIG_XTENSA_LOAD_STORE
 #define LOAD_EXCEPTION_HANDLER
@@ -185,8 +188,12 @@ ENTRY(fast_load_store)
 
 #ifdef CONFIG_MMU
 	/* l32e can't be used here even when it's available. */
-	/* TODO access_ok(a3) could be used here */
-	j	.Linvalid_instruction
+	rsr	a6, ps
+	bbsi.l	a6, PS_UM_BIT, 1f	# user mode
+	j	.Linvalid_instruction	# kernel mode
+1:
+	movi	a5, 8
+	access_ok a3, a5, a6, a2, .Linvalid_instruction
 #endif
 	l32i	a5, a3, 0
 	l32i	a6, a3, 4
-- 
2.43.0