Re: [PATCH V3 14/22] LoongArch: Add signal handling support

From: Arnd Bergmann
Date: Fri Sep 17 2021 - 04:27:15 EST

On Fri, Sep 17, 2021 at 5:57 AM Huacai Chen <chenhuacai@xxxxxxxxxxx> wrote:
>
> This patch adds signal handling support for LoongArch.
>
> Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
> ---
> arch/loongarch/include/asm/abi.h | 27 ++
> arch/loongarch/include/uapi/asm/sigcontext.h | 40 ++
> arch/loongarch/include/uapi/asm/ucontext.h | 35 ++
> arch/loongarch/kernel/signal-common.h | 38 ++
> arch/loongarch/kernel/signal.c | 467 +++++++++++++++++++

Please add Eric Biederman and Al Viro as reviewers to Cc. I have no
further comments
below, but a full quote for them as reference.

Arnd

> diff --git a/arch/loongarch/include/asm/abi.h b/arch/loongarch/include/asm/abi.h
> new file mode 100644
> index 000000000000..ced8534db4df
> --- /dev/null
> +++ b/arch/loongarch/include/asm/abi.h
> @@ -0,0 +1,27 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2020-2021 Loongson Technology Corporation Limited
> + */
> +#ifndef _ASM_ABI_H
> +#define _ASM_ABI_H
> +
> +#include <linux/signal_types.h>
> +
> +#include <asm/signal.h>
> +#include <asm/siginfo.h>
> +#include <asm/vdso.h>
> +
> +struct loongarch_abi {
> + const unsigned long restart;
> + const int audit_arch;
> +
> + unsigned int off_sc_fpregs;
> + unsigned int off_sc_fcc;
> + unsigned int off_sc_fcsr;
> + unsigned int off_sc_vcsr;
> + unsigned int off_sc_flags;
> +
> + struct loongarch_vdso_info *vdso;
> +};
> +
> +#endif /* _ASM_ABI_H */
> diff --git a/arch/loongarch/include/uapi/asm/sigcontext.h b/arch/loongarch/include/uapi/asm/sigcontext.h
> new file mode 100644
> index 000000000000..da0e5bac2d80
> --- /dev/null
> +++ b/arch/loongarch/include/uapi/asm/sigcontext.h
> @@ -0,0 +1,40 @@
> +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
> +/*
> + * Author: Hanlu Li <lihanlu@xxxxxxxxxxx>
> + * Huacai Chen <chenhuacai@xxxxxxxxxxx>
> + *
> + * Copyright (C) 2020-2021 Loongson Technology Corporation Limited
> + */
> +#ifndef _UAPI_ASM_SIGCONTEXT_H
> +#define _UAPI_ASM_SIGCONTEXT_H
> +
> +#include <linux/types.h>
> +#include <asm/processor.h>
> +
> +/* scalar FP context was used */
> +#define USED_FP (1 << 0)
> +
> +/* extended context was used, see struct extcontext for details */
> +#define USED_EXTCONTEXT (1 << 1)
> +
> +#include <linux/posix_types.h>
> +/*
> + * Keep this struct definition in sync with the sigcontext fragment
> + * in arch/loongarch/kernel/asm-offsets.c
> + *
> + */
> +struct sigcontext {
> + __u64 sc_pc;
> + __u64 sc_regs[32];
> + __u32 sc_flags;
> +
> + __u32 sc_fcsr;
> + __u32 sc_vcsr;
> + __u64 sc_fcc;
> + __u64 sc_scr[4];
> +
> + union fpureg sc_fpregs[32] FPU_ALIGN;
> + __u8 sc_reserved[4096] __attribute__((__aligned__(16)));
> +};
> +
> +#endif /* _UAPI_ASM_SIGCONTEXT_H */
> diff --git a/arch/loongarch/include/uapi/asm/ucontext.h b/arch/loongarch/include/uapi/asm/ucontext.h
> new file mode 100644
> index 000000000000..12577e22b1c7
> --- /dev/null
> +++ b/arch/loongarch/include/uapi/asm/ucontext.h
> @@ -0,0 +1,35 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef __LOONGARCH_UAPI_ASM_UCONTEXT_H
> +#define __LOONGARCH_UAPI_ASM_UCONTEXT_H
> +
> +/**
> + * struct ucontext - user context structure
> + * @uc_flags:
> + * @uc_link:
> + * @uc_stack:
> + * @uc_mcontext: holds basic processor state
> + * @uc_sigmask:
> + * @uc_extcontext: holds extended processor state
> + */
> +struct ucontext {
> + unsigned long uc_flags;
> + struct ucontext *uc_link;
> + stack_t uc_stack;
> + sigset_t uc_sigmask;
> + /* There's some padding here to allow sigset_t to be expanded in the
> + * future. Though this is unlikely, other architectures put uc_sigmask
> + * at the end of this structure and explicitly state it can be
> + * expanded, so we didn't want to box ourselves in here. */
> + __u8 __unused[1024 / 8 - sizeof(sigset_t)];
> + /* We can't put uc_sigmask at the end of this structure because we need
> + * to be able to expand sigcontext in the future. For example, the
> + * vector ISA extension will almost certainly add ISA state. We want
> + * to ensure all user-visible ISA state can be saved and restored via a
> + * ucontext, so we're putting this at the end in order to allow for
> + * infinite extensibility. Since we know this will be extended and we
> + * assume sigset_t won't be extended an extreme amount, we're
> + * prioritizing this. */
> + struct sigcontext uc_mcontext;
> +};
> +
> +#endif /* __LOONGARCH_UAPI_ASM_UCONTEXT_H */
> diff --git a/arch/loongarch/kernel/signal-common.h b/arch/loongarch/kernel/signal-common.h
> new file mode 100644
> index 000000000000..1693fbdedeaa
> --- /dev/null
> +++ b/arch/loongarch/kernel/signal-common.h
> @@ -0,0 +1,38 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +/*
> + * Author: Hanlu Li <lihanlu@xxxxxxxxxxx>
> + * Huacai Chen <chenhuacai@xxxxxxxxxxx>
> + *
> + * Copyright (C) 2020-2021 Loongson Technology Corporation Limited
> + */
> +
> +#ifndef __SIGNAL_COMMON_H
> +#define __SIGNAL_COMMON_H
> +
> +/* #define DEBUG_SIG */
> +
> +#ifdef DEBUG_SIG
> +# define DEBUGP(fmt, args...) printk("%s: " fmt, __func__, ##args)
> +#else
> +# define DEBUGP(fmt, args...)
> +#endif
> +
> +/*
> + * Determine which stack to use..
> + */
> +extern void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs,
> + size_t frame_size);
> +/* Check and clear pending FPU exceptions in saved CSR */
> +extern int fpcsr_pending(unsigned int __user *fpcsr);
> +
> +/* Make sure we will not lose FPU ownership */
> +#define lock_fpu_owner() ({ preempt_disable(); pagefault_disable(); })
> +#define unlock_fpu_owner() ({ pagefault_enable(); preempt_enable(); })
> +
> +/* Assembly functions to move context to/from the FPU */
> +extern asmlinkage int
> +_save_fp_context(void __user *fpregs, void __user *fcc, void __user *csr);
> +extern asmlinkage int
> +_restore_fp_context(void __user *fpregs, void __user *fcc, void __user *csr);
> +
> +#endif /* __SIGNAL_COMMON_H */
> diff --git a/arch/loongarch/kernel/signal.c b/arch/loongarch/kernel/signal.c
> new file mode 100644
> index 000000000000..78319d2575c6
> --- /dev/null
> +++ b/arch/loongarch/kernel/signal.c
> @@ -0,0 +1,467 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Author: Hanlu Li <lihanlu@xxxxxxxxxxx>
> + * Huacai Chen <chenhuacai@xxxxxxxxxxx>
> + * Copyright (C) 2020-2021 Loongson Technology Corporation Limited
> + *
> + * Derived from MIPS:
> + * Copyright (C) 1991, 1992 Linus Torvalds
> + * Copyright (C) 1994 - 2000 Ralf Baechle
> + * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
> + * Copyright (C) 2014, Imagination Technologies Ltd.
> + */
> +#include <linux/audit.h>
> +#include <linux/cache.h>
> +#include <linux/context_tracking.h>
> +#include <linux/irqflags.h>
> +#include <linux/sched.h>
> +#include <linux/mm.h>
> +#include <linux/personality.h>
> +#include <linux/smp.h>
> +#include <linux/kernel.h>
> +#include <linux/signal.h>
> +#include <linux/errno.h>
> +#include <linux/wait.h>
> +#include <linux/ptrace.h>
> +#include <linux/unistd.h>
> +#include <linux/uprobes.h>
> +#include <linux/compiler.h>
> +#include <linux/syscalls.h>
> +#include <linux/uaccess.h>
> +#include <linux/tracehook.h>
> +
> +#include <asm/abi.h>
> +#include <asm/asm.h>
> +#include <asm/cacheflush.h>
> +#include <asm/fpu.h>
> +#include <asm/ucontext.h>
> +#include <asm/cpu-features.h>
> +
> +#include "signal-common.h"
> +
> +static int (*save_fp_context)(void __user *sc);
> +static int (*restore_fp_context)(void __user *sc);
> +
> +struct rt_sigframe {
> + struct siginfo rs_info;
> + struct ucontext rs_uctx;
> +};
> +
> +/*
> + * Thread saved context copy to/from a signal context presumed to be on the
> + * user stack, and therefore accessed with appropriate macros from uaccess.h.
> + */
> +static int copy_fp_to_sigcontext(void __user *sc)
> +{
> + struct loongarch_abi *abi = current->thread.abi;
> + uint64_t __user *fpregs = sc + abi->off_sc_fpregs;
> + uint64_t __user *fcc = sc + abi->off_sc_fcc;
> + uint32_t __user *csr = sc + abi->off_sc_fcsr;
> + int i;
> + int err = 0;
> + int inc = 1;
> +
> + for (i = 0; i < NUM_FPU_REGS; i += inc) {
> + err |=
> + __put_user(get_fpr64(&current->thread.fpu.fpr[i], 0),
> + &fpregs[4*i]);
> + }
> + err |= __put_user(current->thread.fpu.fcsr, csr);
> + err |= __put_user(current->thread.fpu.fcc, fcc);
> +
> + return err;
> +}
> +
> +static int copy_fp_from_sigcontext(void __user *sc)
> +{
> + struct loongarch_abi *abi = current->thread.abi;
> + uint64_t __user *fpregs = sc + abi->off_sc_fpregs;
> + uint64_t __user *fcc = sc + abi->off_sc_fcc;
> + uint32_t __user *csr = sc + abi->off_sc_fcsr;
> + int i;
> + int err = 0;
> + int inc = 1;
> + u64 fpr_val;
> +
> + for (i = 0; i < NUM_FPU_REGS; i += inc) {
> + err |= __get_user(fpr_val, &fpregs[4*i]);
> + set_fpr64(&current->thread.fpu.fpr[i], 0, fpr_val);
> + }
> + err |= __get_user(current->thread.fpu.fcsr, csr);
> + err |= __get_user(current->thread.fpu.fcc, fcc);
> +
> + return err;
> +}
> +
> +/*
> + * Wrappers for the assembly _{save,restore}_fp_context functions.
> + */
> +static int save_hw_fp_context(void __user *sc)
> +{
> + struct loongarch_abi *abi = current->thread.abi;
> + uint64_t __user *fpregs = sc + abi->off_sc_fpregs;
> + uint64_t __user *fcc = sc + abi->off_sc_fcc;
> + uint32_t __user *fcsr = sc + abi->off_sc_fcsr;
> +
> + return _save_fp_context(fpregs, fcc, fcsr);
> +}
> +
> +static int restore_hw_fp_context(void __user *sc)
> +{
> + struct loongarch_abi *abi = current->thread.abi;
> + uint64_t __user *fpregs = sc + abi->off_sc_fpregs;
> + uint64_t __user *fcc = sc + abi->off_sc_fcc;
> + uint32_t __user *csr = sc + abi->off_sc_fcsr;
> +
> + return _restore_fp_context(fpregs, fcc, csr);
> +}
> +
> +/*
> + * Helper routines
> + */
> +static int protected_save_fp_context(void __user *sc)
> +{
> + int err = 0;
> + unsigned int used;
> + struct loongarch_abi *abi = current->thread.abi;
> + uint64_t __user *fpregs = sc + abi->off_sc_fpregs;
> + uint32_t __user *fcc = sc + abi->off_sc_fcsr;
> + uint32_t __user *fcsr = sc + abi->off_sc_fcsr;
> + uint32_t __user *vcsr = sc + abi->off_sc_vcsr;
> + uint32_t __user *flags = sc + abi->off_sc_flags;
> +
> + used = used_math() ? USED_FP : 0;
> + if (!used)
> + goto fp_done;
> +
> + while (1) {
> + lock_fpu_owner();
> + if (is_fpu_owner())
> + err = save_fp_context(sc);
> + else
> + err |= copy_fp_to_sigcontext(sc);
> + unlock_fpu_owner();
> + if (likely(!err))
> + break;
> + /* touch the sigcontext and try again */
> + err = __put_user(0, &fpregs[0]) |
> + __put_user(0, &fpregs[32*4 - 1]) |
> + __put_user(0, fcc) |
> + __put_user(0, fcsr) |
> + __put_user(0, vcsr);
> + if (err)
> + return err; /* really bad sigcontext */
> + }
> +
> +fp_done:
> + return __put_user(used, flags);
> +}
> +
> +static int protected_restore_fp_context(void __user *sc)
> +{
> + unsigned int used;
> + int err = 0, sig = 0, tmp __maybe_unused;
> + struct loongarch_abi *abi = current->thread.abi;
> + uint64_t __user *fpregs = sc + abi->off_sc_fpregs;
> + uint32_t __user *fcsr = sc + abi->off_sc_fcsr;
> + uint32_t __user *fcc = sc + abi->off_sc_fcsr;
> + uint32_t __user *vcsr = sc + abi->off_sc_vcsr;
> + uint32_t __user *flags = sc + abi->off_sc_flags;
> +
> + err = __get_user(used, flags);
> + conditional_used_math(used & USED_FP);
> +
> + /*
> + * The signal handler may have used FPU; give it up if the program
> + * doesn't want it following sigreturn.
> + */
> + if (err || !(used & USED_FP))
> + lose_fpu(0);
> +
> + if (err)
> + return err;
> +
> + if (!(used & USED_FP))
> + goto fp_done;
> +
> + err = sig = fpcsr_pending(fcsr);
> + if (err < 0)
> + return err;
> +
> + while (1) {
> + lock_fpu_owner();
> + if (is_fpu_owner())
> + err = restore_fp_context(sc);
> + else
> + err |= copy_fp_from_sigcontext(sc);
> + unlock_fpu_owner();
> + if (likely(!err))
> + break;
> + /* touch the sigcontext and try again */
> + err = __get_user(tmp, &fpregs[0]) |
> + __get_user(tmp, &fpregs[32*4 - 1]) |
> + __get_user(tmp, fcc) |
> + __get_user(tmp, fcsr) |
> + __get_user(tmp, vcsr);
> + if (err)
> + break; /* really bad sigcontext */
> + }
> +
> +fp_done:
> + return err ?: sig;
> +}
> +
> +static int setup_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
> +{
> + int err = 0;
> + int i;
> +
> + err |= __put_user(regs->csr_epc, &sc->sc_pc);
> +
> + err |= __put_user(0, &sc->sc_regs[0]);
> + for (i = 1; i < 32; i++)
> + err |= __put_user(regs->regs[i], &sc->sc_regs[i]);
> +
> + /*
> + * Save FPU state to signal context. Signal handler
> + * will "inherit" current FPU state.
> + */
> + err |= protected_save_fp_context(sc);
> +
> + return err;
> +}
> +
> +int fpcsr_pending(unsigned int __user *fpcsr)
> +{
> + int err, sig = 0;
> + unsigned int csr, enabled;
> +
> + err = __get_user(csr, fpcsr);
> + enabled = ((csr & FPU_CSR_ALL_E) << 24);
> + /*
> + * If the signal handler set some FPU exceptions, clear it and
> + * send SIGFPE.
> + */
> + if (csr & enabled) {
> + csr &= ~enabled;
> + err |= __put_user(csr, fpcsr);
> + sig = SIGFPE;
> + }
> + return err ?: sig;
> +}
> +
> +static int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
> +{
> + int err = 0;
> + int i;
> +
> + /* Always make any pending restarted system calls return -EINTR */
> + current->restart_block.fn = do_no_restart_syscall;
> +
> + err |= __get_user(regs->csr_epc, &sc->sc_pc);
> +
> + for (i = 1; i < 32; i++)
> + err |= __get_user(regs->regs[i], &sc->sc_regs[i]);
> +
> + return err ?: protected_restore_fp_context(sc);
> +}
> +
> +void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs,
> + size_t frame_size)
> +{
> + unsigned long sp;
> +
> + /* Default to using normal stack */
> + sp = regs->regs[3];
> + sp -= 32; /* Reserve 32-bytes. */
> +
> + sp = sigsp(sp, ksig);
> +
> + return (void __user *)((sp - frame_size) & ALMASK);
> +}
> +
> +/*
> + * Atomically swap in the new signal mask, and wait for a signal.
> + */
> +
> +asmlinkage long sys_rt_sigreturn(void)
> +{
> + struct rt_sigframe __user *frame;
> + struct pt_regs *regs;
> + sigset_t set;
> + int sig;
> +
> + regs = current_pt_regs();
> + frame = (struct rt_sigframe __user *)regs->regs[3];
> + if (!access_ok(frame, sizeof(*frame)))
> + goto badframe;
> + if (__copy_from_user(&set, &frame->rs_uctx.uc_sigmask, sizeof(set)))
> + goto badframe;
> +
> + set_current_blocked(&set);
> +
> + sig = restore_sigcontext(regs, &frame->rs_uctx.uc_mcontext);
> + if (sig < 0)
> + goto badframe;
> + else if (sig)
> + force_sig(sig);
> +
> + if (restore_altstack(&frame->rs_uctx.uc_stack))
> + goto badframe;
> +
> + return regs->regs[4];
> +
> +badframe:
> + force_sig(SIGSEGV);
> + return 0;
> +}
> +
> +static int setup_rt_frame(void *sig_return, struct ksignal *ksig,
> + struct pt_regs *regs, sigset_t *set)
> +{
> + struct rt_sigframe __user *frame;
> + int err = 0;
> +
> + frame = get_sigframe(ksig, regs, sizeof(*frame));
> + if (!access_ok(frame, sizeof(*frame)))
> + return -EFAULT;
> +
> + /* Create siginfo. */
> + err |= copy_siginfo_to_user(&frame->rs_info, &ksig->info);
> +
> + /* Create the ucontext. */
> + err |= __put_user(0, &frame->rs_uctx.uc_flags);
> + err |= __put_user(NULL, &frame->rs_uctx.uc_link);
> + err |= __save_altstack(&frame->rs_uctx.uc_stack, regs->regs[3]);
> + err |= setup_sigcontext(regs, &frame->rs_uctx.uc_mcontext);
> + err |= __copy_to_user(&frame->rs_uctx.uc_sigmask, set, sizeof(*set));
> +
> + if (err)
> + return -EFAULT;
> +
> + /*
> + * Arguments to signal handler:
> + *
> + * a0 = signal number
> + * a1 = 0 (should be cause)
> + * a2 = pointer to ucontext
> + *
> + * $25 and c0_epc point to the signal handler, $29 points to
> + * the struct rt_sigframe.
> + */
> + regs->regs[4] = ksig->sig;
> + regs->regs[5] = (unsigned long) &frame->rs_info;
> + regs->regs[6] = (unsigned long) &frame->rs_uctx;
> + regs->regs[3] = (unsigned long) frame;
> + regs->regs[1] = (unsigned long) sig_return;
> + regs->csr_epc = (unsigned long) ksig->ka.sa.sa_handler;
> +
> + DEBUGP("SIG deliver (%s:%d): sp=0x%p pc=0x%lx ra=0x%lx\n",
> + current->comm, current->pid,
> + frame, regs->csr_epc, regs->regs[1]);
> +
> + return 0;
> +}
> +
> +struct loongarch_abi loongarch_abi = {
> + .restart = __NR_restart_syscall,
> +#ifdef CONFIG_32BIT
> + .audit_arch = AUDIT_ARCH_LOONGARCH32,
> +#else
> + .audit_arch = AUDIT_ARCH_LOONGARCH64,
> +#endif
> +
> + .off_sc_fpregs = offsetof(struct sigcontext, sc_fpregs),
> + .off_sc_fcc = offsetof(struct sigcontext, sc_fcc),
> + .off_sc_fcsr = offsetof(struct sigcontext, sc_fcsr),
> + .off_sc_vcsr = offsetof(struct sigcontext, sc_vcsr),
> + .off_sc_flags = offsetof(struct sigcontext, sc_flags),
> +
> + .vdso = &vdso_info,
> +};
> +
> +static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
> +{
> + int ret;
> + sigset_t *oldset = sigmask_to_save();
> + struct loongarch_abi *abi = current->thread.abi;
> + void *vdso = current->mm->context.vdso;
> +
> + /* Are we from a system call? */
> + if (regs->regs[0]) {
> + switch (regs->regs[4]) {
> + case -ERESTART_RESTARTBLOCK:
> + case -ERESTARTNOHAND:
> + regs->regs[4] = -EINTR;
> + break;
> + case -ERESTARTSYS:
> + if (!(ksig->ka.sa.sa_flags & SA_RESTART)) {
> + regs->regs[4] = -EINTR;
> + break;
> + }
> + fallthrough;
> + case -ERESTARTNOINTR:
> + regs->regs[4] = regs->orig_a0;
> + regs->csr_epc -= 4;
> + }
> +
> + regs->regs[0] = 0; /* Don't deal with this again. */
> + }
> +
> + rseq_signal_deliver(ksig, regs);
> +
> + ret = setup_rt_frame(vdso + abi->vdso->offset_sigreturn, ksig, regs, oldset);
> +
> + signal_setup_done(ret, ksig, 0);
> +}
> +
> +void arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal)
> +{
> + struct ksignal ksig;
> +
> + if (has_signal && get_signal(&ksig)) {
> + /* Whee! Actually deliver the signal. */
> + handle_signal(&ksig, regs);
> + return;
> + }
> +
> + /* Are we from a system call? */
> + if (regs->regs[0]) {
> + switch (regs->regs[4]) {
> + case -ERESTARTNOHAND:
> + case -ERESTARTSYS:
> + case -ERESTARTNOINTR:
> + regs->regs[4] = regs->orig_a0;
> + regs->csr_epc -= 4;
> + break;
> +
> + case -ERESTART_RESTARTBLOCK:
> + regs->regs[4] = regs->orig_a0;
> + regs->regs[11] = current->thread.abi->restart;
> + regs->csr_epc -= 4;
> + break;
> + }
> + regs->regs[0] = 0; /* Don't deal with this again. */
> + }
> +
> + /*
> + * If there's no signal to deliver, we just put the saved sigmask
> + * back
> + */
> + restore_saved_sigmask();
> +}
> +
> +static int signal_setup(void)
> +{
> + if (cpu_has_fpu) {
> + save_fp_context = save_hw_fp_context;
> + restore_fp_context = restore_hw_fp_context;
> + } else {
> + save_fp_context = copy_fp_to_sigcontext;
> + restore_fp_context = copy_fp_from_sigcontext;
> + }
> +
> + return 0;
> +}
> +
> +arch_initcall(signal_setup);
> --
> 2.27.0
>