The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From c08b4848f596fd95543197463b5162bd7bab2442 Mon Sep 17 00:00:00 2001 From: Chen Lifu chenlifu@huawei.com Date: Wed, 15 Jun 2022 09:47:14 +0800 Subject: [PATCH] riscv: lib: uaccess: fix CSR_STATUS SR_SUM bit
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@huawei.com Reviewed-by: Ben Dooks ben.dooks@codethink.co.uk Link: https://lore.kernel.org/r/20220615014714.1650349-1-chenlifu@huawei.com Cc: stable@vger.kernel.org Signed-off-by: Palmer Dabbelt palmer@rivosinc.com
diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S index 8c475f4da308..ec486e5369d9 100644 --- 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)