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From: yunhui cui <cuiyunhui@bytedance.com>
Date: Wed, 27 Mar 2024 16:43:31 +0800
Message-ID: <CAEEQ3w=yNEktgUucmKuUvqfwDYYztVX+jofi5Q7hG-yQWcLbTA@mail.gmail.com>
Subject: Re: [External] [PATCH] riscv: process: Fix kernel gp leakage
To: "Stefan O'Rear" <sorear@fastmail.com>
Cc: linux-riscv@lists.infradead.org, Paul Walmsley <paul.walmsley@sifive.com>, 
	Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou <aou@eecs.berkeley.edu>, linux-kernel@vger.kernel.org
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Hi Stefan,

On Wed, Mar 27, 2024 at 2:14=E2=80=AFPM Stefan O'Rear <sorear@fastmail.com>=
 wrote:
>
> childregs represents the registers which are active for the new thread
> in user context. For a kernel thread, childregs->gp is never used since
> the kernel gp is not touched by switch_to. For a user mode helper, the
> gp value can be observed in user space after execve or possibly by other
> means.
>
> Fixes: 7db91e57a0ac ("RISC-V: Task implementation")
> Signed-off-by: Stefan O'Rear <sorear@fastmail.com>
> ---
>  arch/riscv/kernel/process.c | 3 ---
>  1 file changed, 3 deletions(-)
>
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index 92922dbd5b5c..51042f48da17 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -27,8 +27,6 @@
>  #include <asm/vector.h>
>  #include <asm/cpufeature.h>
>
> -register unsigned long gp_in_global __asm__("gp");
> -
>  #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER=
_TASK)
>  #include <linux/stackprotector.h>
>  unsigned long __stack_chk_guard __read_mostly;
> @@ -207,7 +205,6 @@ int copy_thread(struct task_struct *p, const struct k=
ernel_clone_args *args)
>         if (unlikely(args->fn)) {
>                 /* Kernel thread */
>                 memset(childregs, 0, sizeof(struct pt_regs));
> -               childregs->gp =3D gp_in_global;
>                 /* Supervisor/Machine, irqs on: */
>                 childregs->status =3D SR_PP | SR_PIE;
>
> --
> 2.40.1
>
>
Can you help express in more detail what the problem was before fixing it?

Thanks,
Yunhui