[PATCH v6 06/10] powerpc/signal64: Replace setup_sigcontext() w/ unsafe_setup_sigcontext()
Christophe Leroy
christophe.leroy at csgroup.eu
Wed Feb 24 04:12:45 AEDT 2021
Le 21/02/2021 à 02:23, Christopher M. Riedl a écrit :
> Previously setup_sigcontext() performed a costly KUAP switch on every
> uaccess operation. These repeated uaccess switches cause a significant
> drop in signal handling performance.
>
> Rewrite setup_sigcontext() to assume that a userspace write access window
> is open by replacing all uaccess functions with their 'unsafe' versions.
> Modify the callers to first open, call unsafe_setup_sigcontext() and
> then close the uaccess window.
Do you plan to also convert setup_tm_sigcontexts() ?
It would allow to then remove copy_fpr_to_user() and copy_ckfpr_to_user() and maybe other functions too.
Christophe
>
> Signed-off-by: Christopher M. Riedl <cmr at codefail.de>
> ---
> arch/powerpc/kernel/signal_64.c | 71 ++++++++++++++++++++-------------
> 1 file changed, 44 insertions(+), 27 deletions(-)
>
> diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
> index bd8d210c9115..3faaa736ed62 100644
> --- a/arch/powerpc/kernel/signal_64.c
> +++ b/arch/powerpc/kernel/signal_64.c
> @@ -101,9 +101,13 @@ static void prepare_setup_sigcontext(struct task_struct *tsk)
> * Set up the sigcontext for the signal frame.
> */
>
> -static long setup_sigcontext(struct sigcontext __user *sc,
> - struct task_struct *tsk, int signr, sigset_t *set,
> - unsigned long handler, int ctx_has_vsx_region)
> +#define unsafe_setup_sigcontext(sc, tsk, signr, set, handler, \
> + ctx_has_vsx_region, e) \
> + unsafe_op_wrap(__unsafe_setup_sigcontext(sc, tsk, signr, set, \
> + handler, ctx_has_vsx_region), e)
> +static long notrace __unsafe_setup_sigcontext(struct sigcontext __user *sc,
> + struct task_struct *tsk, int signr, sigset_t *set,
> + unsigned long handler, int ctx_has_vsx_region)
> {
> /* When CONFIG_ALTIVEC is set, we _always_ setup v_regs even if the
> * process never used altivec yet (MSR_VEC is zero in pt_regs of
> @@ -118,20 +122,19 @@ static long setup_sigcontext(struct sigcontext __user *sc,
> #endif
> struct pt_regs *regs = tsk->thread.regs;
> unsigned long msr = regs->msr;
> - long err = 0;
> /* Force usr to alway see softe as 1 (interrupts enabled) */
> unsigned long softe = 0x1;
>
> BUG_ON(tsk != current);
>
> #ifdef CONFIG_ALTIVEC
> - err |= __put_user(v_regs, &sc->v_regs);
> + unsafe_put_user(v_regs, &sc->v_regs, efault_out);
>
> /* save altivec registers */
> if (tsk->thread.used_vr) {
> /* Copy 33 vec registers (vr0..31 and vscr) to the stack */
> - err |= __copy_to_user(v_regs, &tsk->thread.vr_state,
> - 33 * sizeof(vector128));
> + unsafe_copy_to_user(v_regs, &tsk->thread.vr_state,
> + 33 * sizeof(vector128), efault_out);
> /* set MSR_VEC in the MSR value in the frame to indicate that sc->v_reg)
> * contains valid data.
> */
> @@ -140,12 +143,12 @@ static long setup_sigcontext(struct sigcontext __user *sc,
> /* We always copy to/from vrsave, it's 0 if we don't have or don't
> * use altivec.
> */
> - err |= __put_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33]);
> + unsafe_put_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33], efault_out);
> #else /* CONFIG_ALTIVEC */
> - err |= __put_user(0, &sc->v_regs);
> + unsafe_put_user(0, &sc->v_regs, efault_out);
> #endif /* CONFIG_ALTIVEC */
> /* copy fpr regs and fpscr */
> - err |= copy_fpr_to_user(&sc->fp_regs, tsk);
> + unsafe_copy_fpr_to_user(&sc->fp_regs, tsk, efault_out);
>
> /*
> * Clear the MSR VSX bit to indicate there is no valid state attached
> @@ -160,24 +163,27 @@ static long setup_sigcontext(struct sigcontext __user *sc,
> */
> if (tsk->thread.used_vsr && ctx_has_vsx_region) {
> v_regs += ELF_NVRREG;
> - err |= copy_vsx_to_user(v_regs, tsk);
> + unsafe_copy_vsx_to_user(v_regs, tsk, efault_out);
> /* set MSR_VSX in the MSR value in the frame to
> * indicate that sc->vs_reg) contains valid data.
> */
> msr |= MSR_VSX;
> }
> #endif /* CONFIG_VSX */
> - err |= __put_user(&sc->gp_regs, &sc->regs);
> + unsafe_put_user(&sc->gp_regs, &sc->regs, efault_out);
> WARN_ON(!FULL_REGS(regs));
> - err |= __copy_to_user(&sc->gp_regs, regs, GP_REGS_SIZE);
> - err |= __put_user(msr, &sc->gp_regs[PT_MSR]);
> - err |= __put_user(softe, &sc->gp_regs[PT_SOFTE]);
> - err |= __put_user(signr, &sc->signal);
> - err |= __put_user(handler, &sc->handler);
> + unsafe_copy_to_user(&sc->gp_regs, regs, GP_REGS_SIZE, efault_out);
> + unsafe_put_user(msr, &sc->gp_regs[PT_MSR], efault_out);
> + unsafe_put_user(softe, &sc->gp_regs[PT_SOFTE], efault_out);
> + unsafe_put_user(signr, &sc->signal, efault_out);
> + unsafe_put_user(handler, &sc->handler, efault_out);
> if (set != NULL)
> - err |= __put_user(set->sig[0], &sc->oldmask);
> + unsafe_put_user(set->sig[0], &sc->oldmask, efault_out);
>
> - return err;
> + return 0;
> +
> +efault_out:
> + return -EFAULT;
> }
>
> #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> @@ -670,12 +676,15 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
>
> if (old_ctx != NULL) {
> prepare_setup_sigcontext(current);
> - if (!access_ok(old_ctx, ctx_size)
> - || setup_sigcontext(&old_ctx->uc_mcontext, current, 0, NULL, 0,
> - ctx_has_vsx_region)
> - || __copy_to_user(&old_ctx->uc_sigmask,
> - ¤t->blocked, sizeof(sigset_t)))
> + if (!user_write_access_begin(old_ctx, ctx_size))
> return -EFAULT;
> +
> + unsafe_setup_sigcontext(&old_ctx->uc_mcontext, current, 0, NULL,
> + 0, ctx_has_vsx_region, efault_out);
> + unsafe_copy_to_user(&old_ctx->uc_sigmask, ¤t->blocked,
> + sizeof(sigset_t), efault_out);
> +
> + user_write_access_end();
> }
> if (new_ctx == NULL)
> return 0;
> @@ -704,6 +713,10 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
> /* This returns like rt_sigreturn */
> set_thread_flag(TIF_RESTOREALL);
> return 0;
> +
> +efault_out:
> + user_write_access_end();
> + return -EFAULT;
> }
>
>
> @@ -854,9 +867,13 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
> } else {
> err |= __put_user(0, &frame->uc.uc_link);
> prepare_setup_sigcontext(tsk);
> - err |= setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
> - NULL, (unsigned long)ksig->ka.sa.sa_handler,
> - 1);
> + if (!user_write_access_begin(&frame->uc.uc_mcontext,
> + sizeof(frame->uc.uc_mcontext)))
> + return -EFAULT;
> + err |= __unsafe_setup_sigcontext(&frame->uc.uc_mcontext, tsk,
> + ksig->sig, NULL,
> + (unsigned long)ksig->ka.sa.sa_handler, 1);
> + user_write_access_end();
> }
> err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
> if (err)
>
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