Re: [PATCH 2/2] riscv: signal: fix signal_minsigstksz

[Andy Chiu]

Hi Yong-Xuan,

Yong-Xuan Wang <yongxuan.wang@xxxxxxxxxx> 於 2024年12月10日 週二 下午10:24寫道：
>
> The init_rt_signal_env() funciton is called before the alternative patch
> is applied, so using the alternative-related API to check the availability
> of an extension within this function doesn't have the intended effect.
> Instead, the riscv_isa bitmap should be used to properly check whether
> given extension is available. This patch also refactors the estimation of
> signal_minsigstksz by extracting it from the get_rt_frame_size() funciton.
>
> Fixes: e92f469b0771 ("riscv: signal: Report signal frame size to userspace via auxv")
> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@xxxxxxxxxx>
> Reviewed-by: Zong Li <zong.li@xxxxxxxxxx>
> ---
>  arch/riscv/kernel/signal.c | 40 ++++++++++++++++++++++++--------------
>  1 file changed, 25 insertions(+), 15 deletions(-)
>
> diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
> index c3c517b9eee5..85eac84719e9 100644
> --- a/arch/riscv/kernel/signal.c
> +++ b/arch/riscv/kernel/signal.c
> @@ -203,22 +203,18 @@ static long restore_sigcontext(struct pt_regs *regs,
>         return err;
>  }
>
> -static size_t get_rt_frame_size(bool cal_all)
> +static size_t get_rt_frame_size(struct pt_regs *regs)
>  {
>         struct rt_sigframe __user *frame;
> -       size_t frame_size;
> +       size_t frame_size = sizeof(*frame);
>         size_t total_context_size = 0;
>
> -       frame_size = sizeof(*frame);
> -
> -       if (has_vector()) {
> -               if (cal_all || riscv_v_vstate_query(task_pt_regs(current)))
> -                       total_context_size += riscv_v_sc_size;
> -       }
> +       if (has_vector() && riscv_v_vstate_query(regs))
> +               total_context_size += riscv_v_sc_size;
>
>         frame_size += total_context_size;
> -
>         frame_size = round_up(frame_size, 16);
> +
>         return frame_size;
>  }
>
> @@ -228,7 +224,7 @@ SYSCALL_DEFINE0(rt_sigreturn)
>         struct rt_sigframe __user *frame;
>         struct task_struct *task;
>         sigset_t set;
> -       size_t frame_size = get_rt_frame_size(false);
> +       size_t frame_size = get_rt_frame_size(regs);
>
>         /* Always make any pending restarted system calls return -EINTR */
>         current->restart_block.fn = do_no_restart_syscall;
> @@ -318,7 +314,7 @@ static int setup_rt_frame(struct ksignal *ksig, sigset_t *set,
>         struct rt_sigframe __user *frame;
>         long err = 0;
>         unsigned long __maybe_unused addr;
> -       size_t frame_size = get_rt_frame_size(false);
> +       size_t frame_size = get_rt_frame_size(regs);
>
>         frame = get_sigframe(ksig, regs, frame_size);
>         if (!access_ok(frame, frame_size))
> @@ -465,19 +461,33 @@ void arch_do_signal_or_restart(struct pt_regs *regs)
>  void init_rt_signal_env(void);
>  void __init init_rt_signal_env(void)
>  {
> -       riscv_v_sc_size = sizeof(struct __riscv_ctx_hdr) +
> -                         sizeof(struct __sc_riscv_v_state) + riscv_v_vsize;
> +       struct rt_sigframe __user *frame;
> +       size_t frame_size = sizeof(*frame);
> +
> +       /*
> +        * init_rt_signal_env() is called before applying alternative patch. Do not use
> +        * __riscv_has_extension_likely()/__riscv_has_extension_unlikely() to check the
> +        * availiablity of an extension in this function.
> +        */
> +       if (__riscv_isa_extension_available(NULL, RISCV_ISA_EXT_v)) {

This should also check for IS_ENABLED(CONFIG_RISCV_ISA_V). Another way
to do this is to call init_rt_signal_env() after
apply_boot_alternative(). This can make assumptions on different piece
of code more coherent. What do you think?


> +               riscv_v_sc_size = sizeof(struct __riscv_ctx_hdr) +
> +                                 sizeof(struct __sc_riscv_v_state) + riscv_v_vsize;
> +               frame_size += riscv_v_sc_size;
> +       }
> +
> +       frame_size = round_up(frame_size, 16);
> +
>         /*
>          * Determine the stack space required for guaranteed signal delivery.
>          * The signal_minsigstksz will be populated into the AT_MINSIGSTKSZ entry
>          * in the auxiliary array at process startup.
>          */
> -       signal_minsigstksz = get_rt_frame_size(true);
> +       signal_minsigstksz = frame_size;
>  }
>
>  #ifdef CONFIG_DYNAMIC_SIGFRAME
>  bool sigaltstack_size_valid(size_t ss_size)
>  {
> -       return ss_size > get_rt_frame_size(false);
> +       return ss_size > get_rt_frame_size(current_pt_regs());
>  }
>  #endif /* CONFIG_DYNAMIC_SIGFRAME */
> --
> 2.17.1
>

Thanks,
Andy