[PATCH 5.15 025/136] riscv: lib: uaccess: fix CSR_STATUS SR_SUM bit

[Greg Kroah-Hartman]

From: Chen Lifu <chenlifu@xxxxxxxxxx>

[ Upstream commit c08b4848f596fd95543197463b5162bd7bab2442 ]

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@xxxxxxxxxx>
Reviewed-by: Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220615014714.1650349-1-chenlifu@xxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/riscv/lib/uaccess.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S
index ac34f0026adcd..2c7c1c5026af3 100644
--- a/arch/riscv/lib/uaccess.S
+++ b/arch/riscv/lib/uaccess.S
@@ -177,7 +177,7 @@ 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)
@@ -229,7 +229,7 @@ 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)
-- 
2.35.1