[PATCH v3 2/2] riscv/mm: Prevent kernel module to access user memory without uaccess routines

[Eric Lin]

We found this issue in an legacy out-of-tree kernel module
which didn't properly access user space pointer by get/put_user().
Such an illegal access loops in the page fault handler.
To resolve this, let it die here.

Signed-off-by: Eric Lin <tesheng at andestech.com>
Cc: Alan Kao <alankao at andestech.com>
Reviewed-by: Pekka Enberg <penberg at kernel.org>
---
 arch/riscv/mm/fault.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index 0d5f06d6e3c7..33d284188f9a 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -243,6 +243,11 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
 
+	if (!user_mode(regs) && addr < TASK_SIZE &&
+			unlikely(!(regs->status & SR_SUM)))
+		die_kernel_fault("access to user memory without uaccess routines",
+				addr, regs);
+
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
 
 	if (cause == EXC_STORE_PAGE_FAULT)
-- 
2.17.0