powerpc/signal64: Replace restore_sigcontext() w/ unsafe_restore_sigcontext()

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 by replacing all uaccess functions with their 'unsafe'
versions. Modify the callers to first open, call
unsafe_restore_sigcontext(), and then close the uaccess window.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210227011259.11992-8-cmr@codefail.de

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 78ae4bb..23a44ec 100644 (file)
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -327,14 +327,16 @@ 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, label) do {       \
+       if (__unsafe_restore_sigcontext(tsk, set, sig, sc))             \
+               goto label;                                             \
+} while (0)
+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;
@@ -349,27 +351,27 @@ 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.
@@ -379,29 +381,27 @@ 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
@@ -410,14 +410,17 @@ 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
@@ -708,8 +711,14 @@ 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);
@@ -812,8 +821,13 @@ 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->uc_mcontext, sizeof(uc->uc_mcontext)))
+                       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))