linux-kernel - [PATCH 1/4] riscv: __asm_copy_to-from

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Date:   Tue, 20 Jul 2021 17:50:52 +0900
From:   Akira Tsukamoto <akira.tsukamoto@...il.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] riscv: __asm_copy_to-from_user: Fix: overrun copy


There were two causes for the overrun memory access.

The threshold size was too small.
The aligning dst require one SZREG and unrolling word copy requires
8*SZREG, total have to be at least 9*SZREG.

Inside the unrolling copy, the subtracting -(8*SZREG-1) would make
iteration happening one extra loop. Proper value is -(8*SZREG).

Signed-off-by: Akira Tsukamoto <akira.tsukamoto@...il.com>
---
 arch/riscv/lib/uaccess.S | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S
index bceb0629e440..8bbeca89a93f 100644
--- a/arch/riscv/lib/uaccess.S
+++ b/arch/riscv/lib/uaccess.S
@@ -35,7 +35,7 @@ ENTRY(__asm_copy_from_user)
 	/*
 	 * Use byte copy only if too small.
 	 */
-	li	a3, 8*SZREG /* size must be larger than size in word_copy */
+	li	a3, 9*SZREG /* size must be larger than size in word_copy */
 	bltu	a2, a3, .Lbyte_copy_tail
 
 	/*
@@ -75,7 +75,7 @@ ENTRY(__asm_copy_from_user)
 	 * a3 - a1 & mask:(SZREG-1)
 	 * t0 - end of aligned dst
 	 */
-	addi	t0, t0, -(8*SZREG-1) /* not to over run */
+	addi	t0, t0, -(8*SZREG) /* not to over run */
 2:
 	fixup REG_L   a4,        0(a1), 10f
 	fixup REG_L   a5,    SZREG(a1), 10f
@@ -97,7 +97,7 @@ ENTRY(__asm_copy_from_user)
 	addi	a1, a1, 8*SZREG
 	bltu	a0, t0, 2b
 
-	addi	t0, t0, 8*SZREG-1 /* revert to original value */
+	addi	t0, t0, 8*SZREG /* revert to original value */
 	j	.Lbyte_copy_tail
 
 .Lshift_copy:
-- 
2.17.1