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SubjectRe: [PATCH] riscv/mm: Prevent kernel module access user-space memory without uaccess routines
On Mon, Nov 30, 2020 at 7:33 AM Eric Lin <tesheng@andestech.com> wrote:
>
> In the page fault handler, an access to user-space memory
> without get/put_user() or copy_from/to_user() routines is
> not resolved properly. Like arm and other architectures,
> we need to let it die earlier in page fault handler.

Fix looks good to me. Can you elaborate on how you found the issue and
how the bug manifests itself?

>
> Signed-off-by: Eric Lin <tesheng@andestech.com>
> Cc: Alan Kao <alankao@andestech.com>
> ---
> arch/riscv/mm/fault.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> index 3c8b9e433c67..a452cfa266a2 100644
> --- a/arch/riscv/mm/fault.c
> +++ b/arch/riscv/mm/fault.c
> @@ -232,6 +232,9 @@ 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(regs, "Accessing user space memory without uaccess routines\n");

Let's introduce a die_kernel_fault() helper (similar to arm64, for
example) to ensure same semantics for the different kernel faults. You
can extract the helper from no_context().

> +
> perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
>
> if (cause == EXC_STORE_PAGE_FAULT)
> --
> 2.17.0
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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