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

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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
This commit is contained in:
Christopher M. Riedl 2021-02-26 19:12:56 -06:00 committed by Michael Ellerman
parent 7bb081c8f0
commit 193323e100
1 changed files with 41 additions and 27 deletions
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68
arch/powerpc/kernel/signal_64.c
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@ -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))