Commit 7bb081c8 authored by Christopher M. Riedl's avatar Christopher M. Riedl Committed by Michael Ellerman
Browse files

powerpc/signal64: Replace setup_sigcontext() w/ unsafe_setup_sigcontext() 



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.

Signed-off-by: default avatarChristopher M. Riedl <cmr@codefail.de>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210227011259.11992-7-cmr@codefail.de
parent 2d19630e

arch/powerpc/kernel/signal_64.c

+45 −27
Original line number Diff line number Diff line
@@ -101,7 +101,12 @@ 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,

#define unsafe_setup_sigcontext(sc, tsk, signr, set, handler, ctx_has_vsx_region, label)\

do {											\

	if (__unsafe_setup_sigcontext(sc, tsk, signr, set, handler, ctx_has_vsx_region))\

		goto label;								\

} while (0)

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)

{
@@ -118,20 +123,19 @@ 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 +144,12 @@ 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 +164,27 @@ 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 +677,15 @@ 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,

				      &current->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, &current->blocked,

				    sizeof(sigset_t), efault_out);



		user_write_access_end();

	}

	if (new_ctx == NULL)

		return 0;
@@ -704,6 +714,10 @@ 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 +868,13 @@ 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)