linux-kernel - [PATCH v2 2/2] riscv/mm: Prevent kernel module to access user memory without uaccess routines

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Date:   Thu, 3 Dec 2020 14:48:26 +0800
From:   Eric Lin <tesheng@...estech.com>
To:     <linux-kernel@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
        <walken@...gle.com>, <vbabka@...e.cz>, <peterx@...hat.com>,
        <akpm@...ux-foundation.org>, <penberg@...nel.org>,
        <aou@...s.berkeley.edu>, <palmer@...belt.com>,
        <paul.walmsley@...ive.com>, <hch@...radead.org>
CC:     Eric Lin <tesheng@...estech.com>, Alan Kao <alankao@...estech.com>
Subject: [PATCH v2 2/2] riscv/mm: Prevent kernel module to access user memory without uaccess routines

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@...estech.com>
Cc: Alan Kao <alankao@...estech.com>
---
 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 0bcfd0e1b39e..00884c1bac28 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -245,6 +245,11 @@ 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