Re: [PATCH 03/10] x86/fpu: Split __fpu_restore_sig to extract compat path

[Alexander Mikhalitsyn]

Am Mo., 15. Juni 2026 um 21:38 Uhr schrieb Andrei Vagin <avagin@xxxxxxxxxx>:
>
> Split __fpu_restore_sig to move the restore part for the legacy/compat
> FPU state (when buf_f is present) to a separate helper function.
>
> The legacy 32-bit FP frame duplicates the FP state portion of the
> FX/XSAVE frame. For backward compatibility, the legacy FP frame is
> treated as the source of truth, and its state is folded into the
> FX/XSAVE state before restoring the registers.
>
> Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxxx>

> ---
>  arch/x86/kernel/fpu/signal.c | 50 +++++++++++++++++++++++++++---------
>  1 file changed, 38 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
> index 42c3d78bd849..6a14b528ac7f 100644
> --- a/arch/x86/kernel/fpu/signal.c
> +++ b/arch/x86/kernel/fpu/signal.c
> @@ -264,6 +264,9 @@ static int __restore_fpregs_from_user(void __user *buf, u64 task_xfeatures,
>         }
>  }
>
> +static bool restore_fpregs_from_user_compat(void __user *buf_f, void __user *buf_fx,
> +                                           u64 xrestore_mask, bool fx_only);
> +
>  /*
>   * Attempt to restore the FPU registers directly from user memory.
>   * Pagefaults are handled and any errors returned are fatal.
> @@ -324,14 +327,9 @@ static bool restore_fpregs_from_user(void __user *buf, u64 xrestore_mask, bool f
>         return true;
>  }
>
> -static bool __fpu_restore_sig(void __user *buf_f, void __user *buf_fx,
> -                             bool ia32_fxstate)
> +static bool __fpu_restore_sig(void __user *buf_f, void __user *buf_fx)
>  {
> -       struct task_struct *tsk = current;
> -       struct fpu *fpu = x86_task_fpu(tsk);
> -       struct user_i387_ia32_struct env;
> -       bool success, fx_only = false;
> -       union fpregs_state *fpregs;
> +       bool fx_only = false;
>         u64 xrestore_mask = 0;
>
>         if (use_xsave()) {
> @@ -346,11 +344,33 @@ static bool __fpu_restore_sig(void __user *buf_f, void __user *buf_fx,
>                 xrestore_mask = XFEATURE_MASK_FPSSE;
>         }
>
> -       if (likely(!ia32_fxstate)) {
> +       if (likely(!buf_f)) {
>                 /* Restore the FPU registers directly from user memory. */
>                 return restore_fpregs_from_user(buf_fx, xrestore_mask, fx_only);
>         }
>
> +       return restore_fpregs_from_user_compat(buf_f, buf_fx, xrestore_mask, fx_only);
> +}
> +
> +#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
> +/*
> + * Restore FPU state from a signal frame when a legacy 32-bit FP frame
> + * (buf_f) is present.
> + *
> + * The legacy FP frame duplicates the FP state portion of the FX/XSAVE
> + * frame (buf_fx). For backward compatibility, the legacy FP frame is
> + * treated as the source of truth, and its state is folded into the
> + * FX/XSAVE state before restoring the registers.
> + */
> +static bool restore_fpregs_from_user_compat(void __user *buf_f, void __user *buf_fx,
> +                                           u64 xrestore_mask, bool fx_only)
> +{
> +       struct task_struct *tsk = current;
> +       struct fpu *fpu = x86_task_fpu(tsk);
> +       struct user_i387_ia32_struct env;
> +       union fpregs_state *fpregs;
> +       bool success;
> +
>         /*
>          * Copy the legacy state because the FP portion of the FX frame has
>          * to be ignored for histerical raisins. The legacy state is folded
> @@ -435,6 +455,13 @@ static bool __fpu_restore_sig(void __user *buf_f, void __user *buf_fx,
>         fpregs_unlock();
>         return success;
>  }
> +#else
> +static bool restore_fpregs_from_user_compat(void __user *buf_f, void __user *buf_fx,
> +                                                  u64 xrestore_mask, bool fx_only)
> +{
> +       return false;
> +}
> +#endif
>
>  static inline unsigned int xstate_sigframe_size(struct fpstate *fpstate)
>  {
> @@ -449,8 +476,7 @@ static inline unsigned int xstate_sigframe_size(struct fpstate *fpstate)
>  bool fpu__restore_sig(void __user *buf, int ia32_frame)
>  {
>         struct fpu *fpu = x86_task_fpu(current);
> -       void __user *buf_fx = buf;
> -       bool ia32_fxstate = false;
> +       void __user *buf_fx = buf, *buf_f = NULL;
>         bool success = false;
>         unsigned int size;
>
> @@ -471,7 +497,7 @@ bool fpu__restore_sig(void __user *buf, int ia32_frame)
>         if (ia32_frame && use_fxsr()) {
>                 buf_fx = buf + sizeof(struct fregs_state);
>                 size += sizeof(struct fregs_state);
> -               ia32_fxstate = true;
> +               buf_f = buf;
>         }
>
>         if (!access_ok(buf, size))
> @@ -482,7 +508,7 @@ bool fpu__restore_sig(void __user *buf, int ia32_frame)
>                                            sizeof(struct user_i387_ia32_struct),
>                                            NULL, buf);
>         } else {
> -               success = __fpu_restore_sig(buf, buf_fx, ia32_fxstate);
> +               success = __fpu_restore_sig(buf_f, buf_fx);
>         }
>
>  out:
> --
> 2.54.0.1189.g8c84645362-goog
>
>