[PATCH v5 07/10] powerpc/signal64: Replace restore_sigcontext() w/ unsafe_restore_sigcontext()

Christopher M. Riedl cmr at codefail.de
Thu Feb 18 06:32:16 AEDT 2021


On Fri Feb 12, 2021 at 3:17 PM CST, Daniel Axtens wrote:
> Hi Chris,
>
> > Previously restore_sigcontext() performed a costly KUAP switch on every
> > uaccess operation. These repeated uaccess switches cause a significant
> > drop in signal handling performance.
> >
> > Rewrite restore_sigcontext() to assume that a userspace read access
> > window is open. Replace all uaccess functions with their 'unsafe'
> > versions which avoid the repeated uaccess switches.
> >
>
> Much of the same comments apply here as to the last patch:
> - the commit message might be improved by adding that you are also
> changing the calling functions to open the uaccess window before
> calling into the new unsafe functions
>
> - I have checked that the safe to unsafe conversions look right.
>
> - I think you're opening too wide a window in user_read_access_begin,
> it seems to me that it could be reduced to just the
> uc_mcontext. (Again, not that it makes a difference with the current
> HW.)

Ok, I'll fix these in the next version as well.

>
> Kind regards,
> Daniel
>
> > Signed-off-by: Christopher M. Riedl <cmr at codefail.de>
> > ---
> >  arch/powerpc/kernel/signal_64.c | 68 ++++++++++++++++++++-------------
> >  1 file changed, 41 insertions(+), 27 deletions(-)
> >
> > diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
> > index 4248e4489ff1..d668f8af18fe 100644
> > --- a/arch/powerpc/kernel/signal_64.c
> > +++ b/arch/powerpc/kernel/signal_64.c
> > @@ -326,14 +326,14 @@ static long setup_tm_sigcontexts(struct sigcontext __user *sc,
> >  /*
> >   * Restore the sigcontext from the signal frame.
> >   */
> > -
> > -static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
> > -			      struct sigcontext __user *sc)
> > +#define unsafe_restore_sigcontext(tsk, set, sig, sc, e) \
> > +	unsafe_op_wrap(__unsafe_restore_sigcontext(tsk, set, sig, sc), e)
> > +static long notrace __unsafe_restore_sigcontext(struct task_struct *tsk, sigset_t *set,
> > +						int sig, struct sigcontext __user *sc)
> >  {
> >  #ifdef CONFIG_ALTIVEC
> >  	elf_vrreg_t __user *v_regs;
> >  #endif
> > -	unsigned long err = 0;
> >  	unsigned long save_r13 = 0;
> >  	unsigned long msr;
> >  	struct pt_regs *regs = tsk->thread.regs;
> > @@ -348,27 +348,28 @@ static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
> >  		save_r13 = regs->gpr[13];
> >  
> >  	/* copy the GPRs */
> > -	err |= __copy_from_user(regs->gpr, sc->gp_regs, sizeof(regs->gpr));
> > -	err |= __get_user(regs->nip, &sc->gp_regs[PT_NIP]);
> > +	unsafe_copy_from_user(regs->gpr, sc->gp_regs, sizeof(regs->gpr),
> > +			      efault_out);
> > +	unsafe_get_user(regs->nip, &sc->gp_regs[PT_NIP], efault_out);
> >  	/* get MSR separately, transfer the LE bit if doing signal return */
> > -	err |= __get_user(msr, &sc->gp_regs[PT_MSR]);
> > +	unsafe_get_user(msr, &sc->gp_regs[PT_MSR], efault_out);
> >  	if (sig)
> >  		regs->msr = (regs->msr & ~MSR_LE) | (msr & MSR_LE);
> > -	err |= __get_user(regs->orig_gpr3, &sc->gp_regs[PT_ORIG_R3]);
> > -	err |= __get_user(regs->ctr, &sc->gp_regs[PT_CTR]);
> > -	err |= __get_user(regs->link, &sc->gp_regs[PT_LNK]);
> > -	err |= __get_user(regs->xer, &sc->gp_regs[PT_XER]);
> > -	err |= __get_user(regs->ccr, &sc->gp_regs[PT_CCR]);
> > +	unsafe_get_user(regs->orig_gpr3, &sc->gp_regs[PT_ORIG_R3], efault_out);
> > +	unsafe_get_user(regs->ctr, &sc->gp_regs[PT_CTR], efault_out);
> > +	unsafe_get_user(regs->link, &sc->gp_regs[PT_LNK], efault_out);
> > +	unsafe_get_user(regs->xer, &sc->gp_regs[PT_XER], efault_out);
> > +	unsafe_get_user(regs->ccr, &sc->gp_regs[PT_CCR], efault_out);
> >  	/* Don't allow userspace to set SOFTE */
> >  	set_trap_norestart(regs);
> > -	err |= __get_user(regs->dar, &sc->gp_regs[PT_DAR]);
> > -	err |= __get_user(regs->dsisr, &sc->gp_regs[PT_DSISR]);
> > -	err |= __get_user(regs->result, &sc->gp_regs[PT_RESULT]);
> > +	unsafe_get_user(regs->dar, &sc->gp_regs[PT_DAR], efault_out);
> > +	unsafe_get_user(regs->dsisr, &sc->gp_regs[PT_DSISR], efault_out);
> > +	unsafe_get_user(regs->result, &sc->gp_regs[PT_RESULT], efault_out);
> >  
> >  	if (!sig)
> >  		regs->gpr[13] = save_r13;
> >  	if (set != NULL)
> > -		err |=  __get_user(set->sig[0], &sc->oldmask);
> > +		unsafe_get_user(set->sig[0], &sc->oldmask, efault_out);
> >  
> >  	/*
> >  	 * Force reload of FP/VEC.
> > @@ -378,29 +379,28 @@ static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
> >  	regs->msr &= ~(MSR_FP | MSR_FE0 | MSR_FE1 | MSR_VEC | MSR_VSX);
> >  
> >  #ifdef CONFIG_ALTIVEC
> > -	err |= __get_user(v_regs, &sc->v_regs);
> > -	if (err)
> > -		return err;
> > +	unsafe_get_user(v_regs, &sc->v_regs, efault_out);
> >  	if (v_regs && !access_ok(v_regs, 34 * sizeof(vector128)))
> >  		return -EFAULT;
> >  	/* Copy 33 vec registers (vr0..31 and vscr) from the stack */
> >  	if (v_regs != NULL && (msr & MSR_VEC) != 0) {
> > -		err |= __copy_from_user(&tsk->thread.vr_state, v_regs,
> > -					33 * sizeof(vector128));
> > +		unsafe_copy_from_user(&tsk->thread.vr_state, v_regs,
> > +				      33 * sizeof(vector128), efault_out);
> >  		tsk->thread.used_vr = true;
> >  	} else if (tsk->thread.used_vr) {
> >  		memset(&tsk->thread.vr_state, 0, 33 * sizeof(vector128));
> >  	}
> >  	/* Always get VRSAVE back */
> >  	if (v_regs != NULL)
> > -		err |= __get_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33]);
> > +		unsafe_get_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33],
> > +				efault_out);
> >  	else
> >  		tsk->thread.vrsave = 0;
> >  	if (cpu_has_feature(CPU_FTR_ALTIVEC))
> >  		mtspr(SPRN_VRSAVE, tsk->thread.vrsave);
> >  #endif /* CONFIG_ALTIVEC */
> >  	/* restore floating point */
> > -	err |= copy_fpr_from_user(tsk, &sc->fp_regs);
> > +	unsafe_copy_fpr_from_user(tsk, &sc->fp_regs, efault_out);
> >  #ifdef CONFIG_VSX
> >  	/*
> >  	 * Get additional VSX data. Update v_regs to point after the
> > @@ -409,14 +409,17 @@ static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
> >  	 */
> >  	v_regs += ELF_NVRREG;
> >  	if ((msr & MSR_VSX) != 0) {
> > -		err |= copy_vsx_from_user(tsk, v_regs);
> > +		unsafe_copy_vsx_from_user(tsk, v_regs, efault_out);
> >  		tsk->thread.used_vsr = true;
> >  	} else {
> >  		for (i = 0; i < 32 ; i++)
> >  			tsk->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = 0;
> >  	}
> >  #endif
> > -	return err;
> > +	return 0;
> > +
> > +efault_out:
> > +	return -EFAULT;
> >  }
> >  
> >  #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> > @@ -701,8 +704,14 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
> >  	if (__copy_from_user(&set, &new_ctx->uc_sigmask, sizeof(set)))
> >  		do_exit(SIGSEGV);
> >  	set_current_blocked(&set);
> > -	if (restore_sigcontext(current, NULL, 0, &new_ctx->uc_mcontext))
> > +
> > +	if (!user_read_access_begin(new_ctx, ctx_size))
> > +		return -EFAULT;
> > +	if (__unsafe_restore_sigcontext(current, NULL, 0, &new_ctx->uc_mcontext)) {
> > +		user_read_access_end();
> >  		do_exit(SIGSEGV);
> > +	}
> > +	user_read_access_end();
> >  
> >  	/* This returns like rt_sigreturn */
> >  	set_thread_flag(TIF_RESTOREALL);
> > @@ -807,8 +816,13 @@ SYSCALL_DEFINE0(rt_sigreturn)
> >  		 * causing a TM bad thing.
> >  		 */
> >  		current->thread.regs->msr &= ~MSR_TS_MASK;
> > -		if (restore_sigcontext(current, NULL, 1, &uc->uc_mcontext))
> > +		if (!user_read_access_begin(uc, sizeof(*uc)))
> > +			return -EFAULT;
> > +		if (__unsafe_restore_sigcontext(current, NULL, 1, &uc->uc_mcontext)) {
> > +			user_read_access_end();
> >  			goto badframe;
> > +		}
> > +		user_read_access_end();
> >  	}
> >  
> >  	if (restore_altstack(&uc->uc_stack))
> > -- 
> > 2.26.1



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