linux-kernel - [PATCH 5.18 0061/1095] riscv: lib: uaccess: fix CSR_STATUS SR

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Date:   Mon, 15 Aug 2022 19:51:00 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Chen Lifu <chenlifu@...wei.com>,
        Ben Dooks <ben.dooks@...ethink.co.uk>,
        Palmer Dabbelt <palmer@...osinc.com>
Subject: [PATCH 5.18 0061/1095] riscv: lib: uaccess: fix CSR_STATUS SR_SUM bit

From: Chen Lifu <chenlifu@...wei.com>

commit c08b4848f596fd95543197463b5162bd7bab2442 upstream.

Since commit 5d8544e2d007 ("RISC-V: Generic library routines and assembly")
and commit ebcbd75e3962 ("riscv: Fix the bug in memory access fixup code"),
if __clear_user and __copy_user return from an fixup branch,
CSR_STATUS SR_SUM bit will be set, it is a vulnerability, so that
S-mode memory accesses to pages that are accessible by U-mode will success.
Disable S-mode access to U-mode memory should clear SR_SUM bit.

Fixes: 5d8544e2d007 ("RISC-V: Generic library routines and assembly")
Fixes: ebcbd75e3962 ("riscv: Fix the bug in memory access fixup code")
Signed-off-by: Chen Lifu <chenlifu@...wei.com>
Reviewed-by: Ben Dooks <ben.dooks@...ethink.co.uk>
Link: https://lore.kernel.org/r/20220615014714.1650349-1-chenlifu@huawei.com
Cc: stable@...r.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/riscv/lib/uaccess.S |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/riscv/lib/uaccess.S
+++ b/arch/riscv/lib/uaccess.S
@@ -175,7 +175,7 @@ ENTRY(__asm_copy_from_user)
 	/* Exception fixup code */
 10:
 	/* Disable access to user memory */
-	csrs CSR_STATUS, t6
+	csrc CSR_STATUS, t6
 	mv a0, t5
 	ret
 ENDPROC(__asm_copy_to_user)
@@ -227,7 +227,7 @@ ENTRY(__clear_user)
 	/* Exception fixup code */
 11:
 	/* Disable access to user memory */
-	csrs CSR_STATUS, t6
+	csrc CSR_STATUS, t6
 	mv a0, a1
 	ret
 ENDPROC(__clear_user)