// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/arch/arm/kernel/signal.c
 *
 *  Copyright (C) 1995-2009 Russell King
 */
#include <linux/errno.h>
#include <linux/random.h>
#include <linux/signal.h>
#include <linux/personality.h>
#include <linux/uaccess.h>
#include <linux/resume_user_mode.h>
#include <linux/uprobes.h>
#include <linux/syscalls.h>

#include <asm/elf.h>
#include <asm/cacheflush.h>
#include <asm/traps.h>
#include <asm/unistd.h>
#include <asm/vfp.h>
#include <asm/syscalls.h>

#include "signal.h"

extern const unsigned long sigreturn_codes[17];

static unsigned long signal_return_offset;

#ifdef CONFIG_IWMMXT

static int preserve_iwmmxt_context(struct iwmmxt_sigframe __user *frame)
{
        char kbuf[sizeof(*frame) + 8];
        struct iwmmxt_sigframe *kframe;
        int err = 0;

        /* the iWMMXt context must be 64 bit aligned */
        kframe = (struct iwmmxt_sigframe *)((unsigned long)(kbuf + 8) & ~7);

        if (test_thread_flag(TIF_USING_IWMMXT)) {
                kframe->magic = IWMMXT_MAGIC;
                kframe->size = IWMMXT_STORAGE_SIZE;
                iwmmxt_task_copy(current_thread_info(), &kframe->storage);
        } else {
                /*
                 * For bug-compatibility with older kernels, some space
                 * has to be reserved for iWMMXt even if it's not used.
                 * Set the magic and size appropriately so that properly
                 * written userspace can skip it reliably:
                 */
                *kframe = (struct iwmmxt_sigframe) {
                        .magic = DUMMY_MAGIC,
                        .size  = IWMMXT_STORAGE_SIZE,
                };
        }

        err = __copy_to_user(frame, kframe, sizeof(*kframe));

        return err;
}

static int restore_iwmmxt_context(char __user **auxp)
{
        struct iwmmxt_sigframe __user *frame =
                (struct iwmmxt_sigframe __user *)*auxp;
        char kbuf[sizeof(*frame) + 8];
        struct iwmmxt_sigframe *kframe;

        /* the iWMMXt context must be 64 bit aligned */
        kframe = (struct iwmmxt_sigframe *)((unsigned long)(kbuf + 8) & ~7);
        if (__copy_from_user(kframe, frame, sizeof(*frame)))
                return -1;

        /*
         * For non-iWMMXt threads: a single iwmmxt_sigframe-sized dummy
         * block is discarded for compatibility with setup_sigframe() if
         * present, but we don't mandate its presence.  If some other
         * magic is here, it's not for us:
         */
        if (!test_thread_flag(TIF_USING_IWMMXT) &&
            kframe->magic != DUMMY_MAGIC)
                return 0;

        if (kframe->size != IWMMXT_STORAGE_SIZE)
                return -1;

        if (test_thread_flag(TIF_USING_IWMMXT)) {
                if (kframe->magic != IWMMXT_MAGIC)
                        return -1;

                iwmmxt_task_restore(current_thread_info(), &kframe->storage);
        }

        *auxp += IWMMXT_STORAGE_SIZE;
        return 0;
}

#endif

#ifdef CONFIG_VFP

static int preserve_vfp_context(struct vfp_sigframe __user *frame)
{
        struct vfp_sigframe kframe;
        int err = 0;

        memset(&kframe, 0, sizeof(kframe));
        kframe.magic = VFP_MAGIC;
        kframe.size = VFP_STORAGE_SIZE;

        err = vfp_preserve_user_clear_hwstate(&kframe.ufp, &kframe.ufp_exc);
        if (err)
                return err;

        return __copy_to_user(frame, &kframe, sizeof(kframe));
}

static int restore_vfp_context(char __user **auxp)
{
        struct vfp_sigframe frame;
        int err;

        err = __copy_from_user(&frame, *auxp, sizeof(frame));
        if (err)
                return err;

        if (frame.magic != VFP_MAGIC || frame.size != VFP_STORAGE_SIZE)
                return -EINVAL;

        *auxp += sizeof(frame);
        return vfp_restore_user_hwstate(&frame.ufp, &frame.ufp_exc);
}

#endif

/*
 * Do a signal return; undo the signal stack.  These are aligned to 64-bit.
 */

static int restore_sigframe(struct pt_regs *regs, struct sigframe __user *sf)
{
        struct sigcontext context;
        char __user *aux;
        sigset_t set;
        int err;

        err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
        if (err == 0)
                set_current_blocked(&set);

        err |= __copy_from_user(&context, &sf->uc.uc_mcontext, sizeof(context));
        if (err == 0) {
                regs->ARM_r0 = context.arm_r0;
                regs->ARM_r1 = context.arm_r1;
                regs->ARM_r2 = context.arm_r2;
                regs->ARM_r3 = context.arm_r3;
                regs->ARM_r4 = context.arm_r4;
                regs->ARM_r5 = context.arm_r5;
                regs->ARM_r6 = context.arm_r6;
                regs->ARM_r7 = context.arm_r7;
                regs->ARM_r8 = context.arm_r8;
                regs->ARM_r9 = context.arm_r9;
                regs->ARM_r10 = context.arm_r10;
                regs->ARM_fp = context.arm_fp;
                regs->ARM_ip = context.arm_ip;
                regs->ARM_sp = context.arm_sp;
                regs->ARM_lr = context.arm_lr;
                regs->ARM_pc = context.arm_pc;
                regs->ARM_cpsr = context.arm_cpsr;
        }

        err |= !valid_user_regs(regs);

        aux = (char __user *) sf->uc.uc_regspace;
#ifdef CONFIG_IWMMXT
        if (err == 0)
                err |= restore_iwmmxt_context(&aux);
#endif
#ifdef CONFIG_VFP
        if (err == 0)
                err |= restore_vfp_context(&aux);
#endif

        return err;
}

asmlinkage int sys_sigreturn(struct pt_regs *regs)
{
        struct sigframe __user *frame;

        /* Always make any pending restarted system calls return -EINTR */
        current->restart_block.fn = do_no_restart_syscall;

        /*
         * Since we stacked the signal on a 64-bit boundary,
         * then 'sp' should be word aligned here.  If it's
         * not, then the user is trying to mess with us.
         */
        if (regs->ARM_sp & 7)
                goto badframe;

        frame = (struct sigframe __user *)regs->ARM_sp;

        if (!access_ok(frame, sizeof (*frame)))
                goto badframe;

        if (restore_sigframe(regs, frame))
                goto badframe;

        return regs->ARM_r0;

badframe:
        force_sig(SIGSEGV);
        return 0;
}

asmlinkage int sys_rt_sigreturn(struct pt_regs *regs)
{
        struct rt_sigframe __user *frame;

        /* Always make any pending restarted system calls return -EINTR */
        current->restart_block.fn = do_no_restart_syscall;

        /*
         * Since we stacked the signal on a 64-bit boundary,
         * then 'sp' should be word aligned here.  If it's
         * not, then the user is trying to mess with us.
         */
        if (regs->ARM_sp & 7)
                goto badframe;

        frame = (struct rt_sigframe __user *)regs->ARM_sp;

        if (!access_ok(frame, sizeof (*frame)))
                goto badframe;

        if (restore_sigframe(regs, &frame->sig))
                goto badframe;

        if (restore_altstack(&frame->sig.uc.uc_stack))
                goto badframe;

        return regs->ARM_r0;

badframe:
        force_sig(SIGSEGV);
        return 0;
}

static int
setup_sigframe(struct sigframe __user *sf, struct pt_regs *regs, sigset_t *set)
{
        struct aux_sigframe __user *aux;
        struct sigcontext context;
        int err = 0;

        context = (struct sigcontext) {
                .arm_r0        = regs->ARM_r0,
                .arm_r1        = regs->ARM_r1,
                .arm_r2        = regs->ARM_r2,
                .arm_r3        = regs->ARM_r3,
                .arm_r4        = regs->ARM_r4,
                .arm_r5        = regs->ARM_r5,
                .arm_r6        = regs->ARM_r6,
                .arm_r7        = regs->ARM_r7,
                .arm_r8        = regs->ARM_r8,
                .arm_r9        = regs->ARM_r9,
                .arm_r10       = regs->ARM_r10,
                .arm_fp        = regs->ARM_fp,
                .arm_ip        = regs->ARM_ip,
                .arm_sp        = regs->ARM_sp,
                .arm_lr        = regs->ARM_lr,
                .arm_pc        = regs->ARM_pc,
                .arm_cpsr      = regs->ARM_cpsr,

                .trap_no       = current->thread.trap_no,
                .error_code    = current->thread.error_code,
                .fault_address = current->thread.address,
                .oldmask       = set->sig[0],
        };

        err |= __copy_to_user(&sf->uc.uc_mcontext, &context, sizeof(context));

        err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(*set));

        aux = (struct aux_sigframe __user *) sf->uc.uc_regspace;
#ifdef CONFIG_IWMMXT
        if (err == 0)
                err |= preserve_iwmmxt_context(&aux->iwmmxt);
#endif
#ifdef CONFIG_VFP
        if (err == 0)
                err |= preserve_vfp_context(&aux->vfp);
#endif
        err |= __put_user(0, &aux->end_magic);

        return err;
}

static inline void __user *
get_sigframe(struct ksignal *ksig, struct pt_regs *regs, int framesize)
{
        unsigned long sp = sigsp(regs->ARM_sp, ksig);
        void __user *frame;

        /*
         * ATPCS B01 mandates 8-byte alignment
         */
        frame = (void __user *)((sp - framesize) & ~7);

        /*
         * Check that we can actually write to the signal frame.
         */
        if (!access_ok(frame, framesize))
                frame = NULL;

        return frame;
}

static int
setup_return(struct pt_regs *regs, struct ksignal *ksig,
             unsigned long __user *rc, void __user *frame)
{
        unsigned long handler = (unsigned long)ksig->ka.sa.sa_handler;
        unsigned long handler_fdpic_GOT = 0;
        unsigned long retcode;
        unsigned int idx, thumb = 0;
        unsigned long cpsr = regs->ARM_cpsr & ~(PSR_f | PSR_E_BIT);
        bool fdpic = IS_ENABLED(CONFIG_BINFMT_ELF_FDPIC) &&
                     (current->personality & FDPIC_FUNCPTRS);

        if (fdpic) {
                unsigned long __user *fdpic_func_desc =
                                        (unsigned long __user *)handler;
                if (__get_user(handler, &fdpic_func_desc[0]) ||
                    __get_user(handler_fdpic_GOT, &fdpic_func_desc[1]))
                        return 1;
        }

        if (IS_ENABLED(CONFIG_CPU_ENDIAN_BE8))
                cpsr |= PSR_E_BIT;

        /*
         * Maybe we need to deliver a 32-bit signal to a 26-bit task.
         */
        if (ksig->ka.sa.sa_flags & SA_THIRTYTWO)
                cpsr = (cpsr & ~MODE_MASK) | USR_MODE;

#ifdef CONFIG_ARM_THUMB
        if (elf_hwcap & HWCAP_THUMB) {
                /*
                 * The LSB of the handler determines if we're going to
                 * be using THUMB or ARM mode for this signal handler.
                 */
                thumb = handler & 1;

                /*
                 * Clear the If-Then Thumb-2 execution state.  ARM spec
                 * requires this to be all 000s in ARM mode.  Snapdragon
                 * S4/Krait misbehaves on a Thumb=>ARM signal transition
                 * without this.
                 *
                 * We must do this whenever we are running on a Thumb-2
                 * capable CPU, which includes ARMv6T2.  However, we elect
                 * to always do this to simplify the code; this field is
                 * marked UNK/SBZP for older architectures.
                 */
                cpsr &= ~PSR_IT_MASK;

                if (thumb) {
                        cpsr |= PSR_T_BIT;
                } else
                        cpsr &= ~PSR_T_BIT;
        }
#endif

        if (ksig->ka.sa.sa_flags & SA_RESTORER) {
                retcode = (unsigned long)ksig->ka.sa.sa_restorer;
                if (fdpic) {
                        /*
                         * We need code to load the function descriptor.
                         * That code follows the standard sigreturn code
                         * (6 words), and is made of 3 + 2 words for each
                         * variant. The 4th copied word is the actual FD
                         * address that the assembly code expects.
                         */
                        idx = 6 + thumb * 3;
                        if (ksig->ka.sa.sa_flags & SA_SIGINFO)
                                idx += 5;
                        if (__put_user(sigreturn_codes[idx],   rc  ) ||
                            __put_user(sigreturn_codes[idx+1], rc+1) ||
                            __put_user(sigreturn_codes[idx+2], rc+2) ||
                            __put_user(retcode,                rc+3))
                                return 1;
                        goto rc_finish;
                }
        } else {
                idx = thumb << 1;
                if (ksig->ka.sa.sa_flags & SA_SIGINFO)
                        idx += 3;

                /*
                 * Put the sigreturn code on the stack no matter which return
                 * mechanism we use in order to remain ABI compliant
                 */
                if (__put_user(sigreturn_codes[idx],   rc) ||
                    __put_user(sigreturn_codes[idx+1], rc+1))
                        return 1;

rc_finish:
#ifdef CONFIG_MMU
                if (cpsr & MODE32_BIT) {
                        struct mm_struct *mm = current->mm;

                        /*
                         * 32-bit code can use the signal return page
                         * except when the MPU has protected the vectors
                         * page from PL0
                         */
                        retcode = mm->context.sigpage + signal_return_offset +
                                  (idx << 2) + thumb;
                } else
#endif
                {
                        /*
                         * Ensure that the instruction cache sees
                         * the return code written onto the stack.
                         */
                        flush_icache_range((unsigned long)rc,
                                           (unsigned long)(rc + 3));

                        retcode = ((unsigned long)rc) + thumb;
                }
        }

        regs->ARM_r0 = ksig->sig;
        regs->ARM_sp = (unsigned long)frame;
        regs->ARM_lr = retcode;
        regs->ARM_pc = handler;
        if (fdpic)
                regs->ARM_r9 = handler_fdpic_GOT;
        regs->ARM_cpsr = cpsr;

        return 0;
}

static int
setup_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
{
        struct sigframe __user *frame = get_sigframe(ksig, regs, sizeof(*frame));
        int err = 0;

        if (!frame)
                return 1;

        /*
         * Set uc.uc_flags to a value which sc.trap_no would never have.
         */
        err = __put_user(0x5ac3c35a, &frame->uc.uc_flags);

        err |= setup_sigframe(frame, regs, set);
        if (err == 0)
                err = setup_return(regs, ksig, frame->retcode, frame);

        return err;
}

static int
setup_rt_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
{
        struct rt_sigframe __user *frame = get_sigframe(ksig, regs, sizeof(*frame));
        int err = 0;

        if (!frame)
                return 1;

        err |= copy_siginfo_to_user(&frame->info, &ksig->info);

        err |= __put_user(0, &frame->sig.uc.uc_flags);
        err |= __put_user(NULL, &frame->sig.uc.uc_link);

        err |= __save_altstack(&frame->sig.uc.uc_stack, regs->ARM_sp);
        err |= setup_sigframe(&frame->sig, regs, set);
        if (err == 0)
                err = setup_return(regs, ksig, frame->sig.retcode, frame);

        if (err == 0) {
                /*
                 * For realtime signals we must also set the second and third
                 * arguments for the signal handler.
                 *   -- Peter Maydell <pmaydell@chiark.greenend.org.uk> 2000-12-06
                 */
                regs->ARM_r1 = (unsigned long)&frame->info;
                regs->ARM_r2 = (unsigned long)&frame->sig.uc;
        }

        return err;
}

/*
 * OK, we're invoking a handler
 */     
static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
{
        sigset_t *oldset = sigmask_to_save();
        int ret;

        /*
         * Perform fixup for the pre-signal frame.
         */
        rseq_signal_deliver(ksig, regs);

        /*
         * Set up the stack frame
         */
        if (ksig->ka.sa.sa_flags & SA_SIGINFO)
                ret = setup_rt_frame(ksig, oldset, regs);
        else
                ret = setup_frame(ksig, oldset, regs);

        /*
         * Check that the resulting registers are actually sane.
         */
        ret |= !valid_user_regs(regs);

        signal_setup_done(ret, ksig, 0);
}

/*
 * Note that 'init' is a special process: it doesn't get signals it doesn't
 * want to handle. Thus you cannot kill init even with a SIGKILL even by
 * mistake.
 *
 * Note that we go through the signals twice: once to check the signals that
 * the kernel can handle, and then we build all the user-level signal handling
 * stack-frames in one go after that.
 */
static int do_signal(struct pt_regs *regs, int syscall)
{
        unsigned int retval = 0, continue_addr = 0, restart_addr = 0;
        struct ksignal ksig;
        int restart = 0;

        /*
         * If we were from a system call, check for system call restarting...
         */
        if (syscall) {
                continue_addr = regs->ARM_pc;
                restart_addr = continue_addr - (thumb_mode(regs) ? 2 : 4);
                retval = regs->ARM_r0;

                /*
                 * Prepare for system call restart.  We do this here so that a
                 * debugger will see the already changed PSW.
                 */
                switch (retval) {
                case -ERESTART_RESTARTBLOCK:
                        restart -= 2;
                        fallthrough;
                case -ERESTARTNOHAND:
                case -ERESTARTSYS:
                case -ERESTARTNOINTR:
                        restart++;
                        regs->ARM_r0 = regs->ARM_ORIG_r0;
                        regs->ARM_pc = restart_addr;
                        break;
                }
        }

        /*
         * Get the signal to deliver.  When running under ptrace, at this
         * point the debugger may change all our registers ...
         */
        /*
         * Depending on the signal settings we may need to revert the
         * decision to restart the system call.  But skip this if a
         * debugger has chosen to restart at a different PC.
         */
        if (get_signal(&ksig)) {
                /* handler */
                if (unlikely(restart) && regs->ARM_pc == restart_addr) {
                        if (retval == -ERESTARTNOHAND ||
                            retval == -ERESTART_RESTARTBLOCK
                            || (retval == -ERESTARTSYS
                                && !(ksig.ka.sa.sa_flags & SA_RESTART))) {
                                regs->ARM_r0 = -EINTR;
                                regs->ARM_pc = continue_addr;
                        }
                }
                handle_signal(&ksig, regs);
        } else {
                /* no handler */
                restore_saved_sigmask();
                if (unlikely(restart) && regs->ARM_pc == restart_addr) {
                        regs->ARM_pc = continue_addr;
                        return restart;
                }
        }
        return 0;
}

asmlinkage int
do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
{
        /*
         * The assembly code enters us with IRQs off, but it hasn't
         * informed the tracing code of that for efficiency reasons.
         * Update the trace code with the current status.
         */
        trace_hardirqs_off();
        do {
                if (likely(thread_flags & _TIF_NEED_RESCHED)) {
                        schedule();
                } else {
                        if (unlikely(!user_mode(regs)))
                                return 0;
                        local_irq_enable();
                        if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) {
                                int restart = do_signal(regs, syscall);
                                if (unlikely(restart)) {
                                        /*
                                         * Restart without handlers.
                                         * Deal with it without leaving
                                         * the kernel space.
                                         */
                                        return restart;
                                }
                                syscall = 0;
                        } else if (thread_flags & _TIF_UPROBE) {
                                uprobe_notify_resume(regs);
                        } else {
                                resume_user_mode_work(regs);
                        }
                }
                local_irq_disable();
                thread_flags = read_thread_flags();
        } while (thread_flags & _TIF_WORK_MASK);
        return 0;
}

struct page *get_signal_page(void)
{
        unsigned long ptr;
        unsigned offset;
        struct page *page;
        void *addr;

        page = alloc_pages(GFP_KERNEL, 0);

        if (!page)
                return NULL;

        addr = page_address(page);

        /* Poison the entire page */
        memset32(addr, __opcode_to_mem_arm(0xe7fddef1),
                 PAGE_SIZE / sizeof(u32));

        /* Give the signal return code some randomness */
        offset = 0x200 + (get_random_u16() & 0x7fc);
        signal_return_offset = offset;

        /* Copy signal return handlers into the page */
        memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));

        /* Flush out all instructions in this page */
        ptr = (unsigned long)addr;
        flush_icache_range(ptr, ptr + PAGE_SIZE);

        return page;
}

#ifdef CONFIG_DEBUG_RSEQ
asmlinkage void do_rseq_syscall(struct pt_regs *regs)
{
        rseq_syscall(regs);
}
#endif

/*
 * Compile-time assertions for siginfo_t offsets. Check NSIG* as well, as
 * changes likely come with new fields that should be added below.
 */
static_assert(NSIGILL   == 11);
static_assert(NSIGFPE   == 15);
static_assert(NSIGSEGV  == 10);
static_assert(NSIGBUS   == 5);
static_assert(NSIGTRAP  == 6);
static_assert(NSIGCHLD  == 6);
static_assert(NSIGSYS   == 2);
static_assert(sizeof(siginfo_t) == 128);
static_assert(__alignof__(siginfo_t) == 4);
static_assert(offsetof(siginfo_t, si_signo)     == 0x00);
static_assert(offsetof(siginfo_t, si_errno)     == 0x04);
static_assert(offsetof(siginfo_t, si_code)      == 0x08);
static_assert(offsetof(siginfo_t, si_pid)       == 0x0c);
static_assert(offsetof(siginfo_t, si_uid)       == 0x10);
static_assert(offsetof(siginfo_t, si_tid)       == 0x0c);
static_assert(offsetof(siginfo_t, si_overrun)   == 0x10);
static_assert(offsetof(siginfo_t, si_status)    == 0x14);
static_assert(offsetof(siginfo_t, si_utime)     == 0x18);
static_assert(offsetof(siginfo_t, si_stime)     == 0x1c);
static_assert(offsetof(siginfo_t, si_value)     == 0x14);
static_assert(offsetof(siginfo_t, si_int)       == 0x14);
static_assert(offsetof(siginfo_t, si_ptr)       == 0x14);
static_assert(offsetof(siginfo_t, si_addr)      == 0x0c);
static_assert(offsetof(siginfo_t, si_addr_lsb)  == 0x10);
static_assert(offsetof(siginfo_t, si_lower)     == 0x14);
static_assert(offsetof(siginfo_t, si_upper)     == 0x18);
static_assert(offsetof(siginfo_t, si_pkey)      == 0x14);
static_assert(offsetof(siginfo_t, si_perf_data) == 0x10);
static_assert(offsetof(siginfo_t, si_perf_type) == 0x14);
static_assert(offsetof(siginfo_t, si_perf_flags) == 0x18);
static_assert(offsetof(siginfo_t, si_band)      == 0x0c);
static_assert(offsetof(siginfo_t, si_fd)        == 0x10);
static_assert(offsetof(siginfo_t, si_call_addr) == 0x0c);
static_assert(offsetof(siginfo_t, si_syscall)   == 0x10);
static_assert(offsetof(siginfo_t, si_arch)      == 0x14);