2020-11-30 06:07:44

by Eric Lin

Subject: [PATCH] riscv/mm: Prevent kernel module access user-space memory without uaccess routines

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.

Signed-off-by: Eric Lin <[email protected]>
Cc: Alan Kao <[email protected]>
---
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");
+
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);

if (cause == EXC_STORE_PAGE_FAULT)
--
2.17.0

2020-11-30 08:12:42

by Pekka Enberg

Subject: Re: [PATCH] riscv/mm: Prevent kernel module access user-space memory without uaccess routines

On Mon, Nov 30, 2020 at 7:33 AM Eric Lin <[email protected]> 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 <[email protected]>
> Cc: Alan Kao <[email protected]>
> ---
> 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
> [email protected]
> http://lists.infradead.org/mailman/listinfo/linux-riscv

2020-11-30 08:33:48

by Christoph Hellwig

Subject: Re: [PATCH] riscv/mm: Prevent kernel module access user-space memory without uaccess routines

> + if (!user_mode(regs) && addr < TASK_SIZE && unlikely(!(regs->status & SR_SUM)))

Please avoid the overly long line.

2020-12-01 05:45:25

by Eric Lin

Subject: Re: [PATCH] riscv/mm: Prevent kernel module access user-space memory without uaccess routines

On Mon, Nov 30, 2020 at 04:07:03PM +0800, Pekka Enberg wrote:

Hi Pekka,
> On Mon, Nov 30, 2020 at 7:33 AM Eric Lin <[email protected]> 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?

OK, I'll elaborate more on the commit message.

>
> >
> > Signed-off-by: Eric Lin <[email protected]>
> > Cc: Alan Kao <[email protected]>
> > ---
> > 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().

OK, I'll add a die_kernel_fault() helper function in v2.

Thanks for your review.

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

2020-12-01 05:45:26

by Eric Lin

Subject: Re: [PATCH] riscv/mm: Prevent kernel module access user-space memory without uaccess routines

On Mon, Nov 30, 2020 at 04:30:15PM +0800, Christoph Hellwig wrote:
Hi Christoph,
> > + if (!user_mode(regs) && addr < TASK_SIZE && unlikely(!(regs->status & SR_SUM)))
>
> Please avoid the overly long line.
OK, I'll modify it in v2. Thanks for your review.