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@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From c08b4848f596fd95543197463b5162bd7bab2442 Mon Sep 17 00:00:00 2001
From: Chen Lifu <chenlifu@xxxxxxxxxx>
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@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>
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)
