cregit-Linux how code gets into the kernel

Release 4.14 arch/cris/arch-v32/kernel/signal.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2003, Axis Communications AB.
 */

#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/mm.h>
#include <linux/slab.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/stddef.h>
#include <linux/syscalls.h>
#include <linux/vmalloc.h>

#include <asm/io.h>
#include <asm/processor.h>
#include <asm/ucontext.h>
#include <linux/uaccess.h>
#include <arch/hwregs/cpu_vect.h>

extern unsigned long cris_signal_return_page;

/*
 * A syscall in CRIS is really a "break 13" instruction, which is 2
 * bytes. The registers is manipulated so upon return the instruction
 * will be executed again.
 *
 * This relies on that PC points to the instruction after the break call.
 */

#define RESTART_CRIS_SYS(regs) regs->r10 = regs->orig_r10; regs->erp -= 2;

/* Signal frames. */

struct signal_frame {
	
struct sigcontext sc;
	
unsigned long extramask[_NSIG_WORDS - 1];
	
unsigned char retcode[8];	/* Trampoline code. */
};


struct rt_signal_frame {
	
struct siginfo *pinfo;
	
void *puc;
	
struct siginfo info;
	
struct ucontext uc;
	
unsigned char retcode[8];	/* Trampoline code. */
};

void do_signal(int restart, struct pt_regs *regs);
void keep_debug_flags(unsigned long oldccs, unsigned long oldspc,
		      struct pt_regs *regs);


static int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc) { unsigned int err = 0; unsigned long old_usp; /* Always make any pending restarted system calls return -EINTR */ current->restart_block.fn = do_no_restart_syscall; /* * Restore the registers from &sc->regs. sc is already checked * for VERIFY_READ since the signal_frame was previously * checked in sys_sigreturn(). */ if (__copy_from_user(regs, sc, sizeof(struct pt_regs))) goto badframe; /* Make that the user-mode flag is set. */ regs->ccs |= (1 << (U_CCS_BITNR + CCS_SHIFT)); /* Don't perform syscall restarting */ regs->exs = -1; /* Restore the old USP. */ err |= __get_user(old_usp, &sc->usp); wrusp(old_usp); return err; badframe: return 1; }

Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik9591.35%133.33%
Rabin Vincent87.69%133.33%
Andrew Lutomirski10.96%133.33%
Total104100.00%3100.00%


asmlinkage int sys_sigreturn(void) { struct pt_regs *regs = current_pt_regs(); sigset_t set; struct signal_frame __user *frame; unsigned long oldspc = regs->spc; unsigned long oldccs = regs->ccs; frame = (struct signal_frame *) rdusp(); /* * Since the signal is stacked on a dword boundary, the frame * should be dword aligned here as well. It it's not, then the * user is trying some funny business. */ if (((long)frame) & 3) goto badframe; if (!access_ok(VERIFY_READ, frame, sizeof(*frame))) goto badframe; if (__get_user(set.sig[0], &frame->sc.oldmask) || (_NSIG_WORDS > 1 && __copy_from_user(&set.sig[1], frame->extramask, sizeof(frame->extramask)))) goto badframe; set_current_blocked(&set); if (restore_sigcontext(regs, &frame->sc)) goto badframe; keep_debug_flags(oldccs, oldspc, regs); return regs->r10; badframe: force_sig(SIGSEGV, current); return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik17495.60%133.33%
Al Viro73.85%133.33%
Matt Fleming10.55%133.33%
Total182100.00%3100.00%


asmlinkage int sys_rt_sigreturn(void) { struct pt_regs *regs = current_pt_regs(); sigset_t set; struct rt_signal_frame __user *frame; unsigned long oldspc = regs->spc; unsigned long oldccs = regs->ccs; frame = (struct rt_signal_frame *) rdusp(); /* * Since the signal is stacked on a dword boundary, the frame * should be dword aligned here as well. It it's not, then the * user is trying some funny business. */ if (((long)frame) & 3) goto badframe; if (!access_ok(VERIFY_READ, frame, sizeof(*frame))) goto badframe; if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set))) goto badframe; set_current_blocked(&set); if (restore_sigcontext(regs, &frame->uc.uc_mcontext)) goto badframe; if (restore_altstack(&frame->uc.uc_stack)) goto badframe; keep_debug_flags(oldccs, oldspc, regs); return regs->r10; badframe: force_sig(SIGSEGV, current); return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik16394.77%125.00%
Al Viro84.65%250.00%
Matt Fleming10.58%125.00%
Total172100.00%4100.00%

/* Setup a signal frame. */
static int setup_sigcontext(struct sigcontext __user *sc, struct pt_regs *regs, unsigned long mask) { int err; unsigned long usp; err = 0; usp = rdusp(); /* * Copy the registers. They are located first in sc, so it's * possible to use sc directly. */ err |= __copy_to_user(sc, regs, sizeof(struct pt_regs)); err |= __put_user(mask, &sc->oldmask); err |= __put_user(usp, &sc->usp); return err; }

Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik80100.00%1100.00%
Total80100.00%1100.00%

/* Figure out where to put the new signal frame - usually on the stack. */
static inline void __user * get_sigframe(struct ksignal *ksig, size_t frame_size) { unsigned long sp = sigsp(rdusp(), ksig); /* Make sure the frame is dword-aligned. */ sp &= ~3; return (void __user *)(sp - frame_size); }

Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik3982.98%150.00%
Richard Weinberger817.02%150.00%
Total47100.00%2100.00%

/* Grab and setup a signal frame. * * Basically a lot of state-info is stacked, and arranged for the * user-mode program to return to the kernel using either a trampiline * which performs the syscall sigreturn(), or a provided user-mode * trampoline. */
static int setup_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs) { int err; unsigned long return_ip; struct signal_frame __user *frame; err = 0; frame = get_sigframe(ksig, sizeof(*frame)); if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame))) return -EFAULT; err |= setup_sigcontext(&frame->sc, regs, set->sig[0]); if (err) return -EFAULT; if (_NSIG_WORDS > 1) { err |= __copy_to_user(frame->extramask, &set->sig[1], sizeof(frame->extramask)); } if (err) return -EFAULT; /* * Set up to return from user-space. If provided, use a stub * already located in user-space. */ if (ksig->ka.sa.sa_flags & SA_RESTORER) { return_ip = (unsigned long)ksig->ka.sa.sa_restorer; } else { /* Trampoline - the desired return ip is in the signal return page. */ return_ip = cris_signal_return_page; /* * This is movu.w __NR_sigreturn, r9; break 13; * * WE DO NOT USE IT ANY MORE! It's only left here for historical * reasons and because gdb uses it as a signature to notice * signal handler stack frames. */ err |= __put_user(0x9c5f, (short __user*)(frame->retcode+0)); err |= __put_user(__NR_sigreturn, (short __user*)(frame->retcode+2)); err |= __put_user(0xe93d, (short __user*)(frame->retcode+4)); } if (err) return -EFAULT; /* * Set up registers for signal handler. * * Where the code enters now. * Where the code enter later. * First argument, signo. */ regs->erp = (unsigned long) ksig->ka.sa.sa_handler; regs->srp = return_ip; regs->r10 = ksig->sig; /* Actually move the USP to reflect the stacked frame. */ wrusp((unsigned long)frame); return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik25388.15%133.33%
Richard Weinberger3010.45%133.33%
Jesper Nilsson41.39%133.33%
Total287100.00%3100.00%


static int setup_rt_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs) { int err; unsigned long return_ip; struct rt_signal_frame __user *frame; err = 0; frame = get_sigframe(ksig, sizeof(*frame)); if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame))) return -EFAULT; err |= __put_user(&frame->info, &frame->pinfo); err |= __put_user(&frame->uc, &frame->puc); err |= copy_siginfo_to_user(&frame->info, &ksig->info); if (err) return -EFAULT; /* Clear all the bits of the ucontext we don't use. */ err |= __clear_user(&frame->uc, offsetof(struct ucontext, uc_mcontext)); err |= setup_sigcontext(&frame->uc.uc_mcontext, regs, set->sig[0]); err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set)); err |= __save_altstack(&frame->uc.uc_stack, rdusp()); if (err) return -EFAULT; /* * Set up to return from user-space. If provided, use a stub * already located in user-space. */ if (ksig->ka.sa.sa_flags & SA_RESTORER) { return_ip = (unsigned long) ksig->ka.sa.sa_restorer; } else { /* Trampoline - the desired return ip is in the signal return page. */ return_ip = cris_signal_return_page + 6; /* * This is movu.w __NR_rt_sigreturn, r9; break 13; * * WE DO NOT USE IT ANY MORE! It's only left here for historical * reasons and because gdb uses it as a signature to notice * signal handler stack frames. */ err |= __put_user(0x9c5f, (short __user*)(frame->retcode+0)); err |= __put_user(__NR_rt_sigreturn, (short __user*)(frame->retcode+2)); err |= __put_user(0xe93d, (short __user*)(frame->retcode+4)); } if (err) return -EFAULT; /* * Set up registers for signal handler. * * Where the code enters now. * Where the code enters later. * First argument is signo. * Second argument is (siginfo_t *). * Third argument is unused. */ regs->erp = (unsigned long) ksig->ka.sa.sa_handler; regs->srp = return_ip; regs->r10 = ksig->sig; regs->r11 = (unsigned long) &frame->info; regs->r12 = 0; /* Actually move the usp to reflect the stacked frame. */ wrusp((unsigned long)frame); return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik32586.21%125.00%
Richard Weinberger338.75%125.00%
Al Viro153.98%125.00%
Jesper Nilsson41.06%125.00%
Total377100.00%4100.00%

/* Invoke a signal handler to, well, handle the signal. */
static inline void handle_signal(int canrestart, struct ksignal *ksig, struct pt_regs *regs) { sigset_t *oldset = sigmask_to_save(); int ret; /* Check if this got called from a system call. */ if (canrestart) { /* If so, check system call restarting. */ switch (regs->r10) { case -ERESTART_RESTARTBLOCK: case -ERESTARTNOHAND: /* * This means that the syscall should * only be restarted if there was no * handler for the signal, and since * this point isn't reached unless * there is a handler, there's no need * to restart. */ regs->r10 = -EINTR; break; case -ERESTARTSYS: /* * This means restart the syscall if * there is no handler, or the handler * was registered with SA_RESTART. */ if (!(ksig->ka.sa.sa_flags & SA_RESTART)) { regs->r10 = -EINTR; break; } /* Fall through. */ case -ERESTARTNOINTR: /* * This means that the syscall should * be called again after the signal * handler returns. */ RESTART_CRIS_SYS(regs); break; } } /* 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); signal_setup_done(ret, ksig, 0); }

Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik11878.67%114.29%
Richard Weinberger138.67%114.29%
Al Viro106.67%342.86%
Jesper Nilsson85.33%114.29%
Adrian Bunk10.67%114.29%
Total150100.00%7100.00%

/* * 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. * * Also note that the regs structure given here as an argument, is the latest * pushed pt_regs. It may or may not be the same as the first pushed registers * when the initial usermode->kernelmode transition took place. Therefore * we can use user_mode(regs) to see if we came directly from kernel or user * mode below. */
void do_signal(int canrestart, struct pt_regs *regs) { struct ksignal ksig; canrestart = canrestart && ((int)regs->exs >= 0); /* * The common case should go fast, which is why this point is * reached from kernel-mode. If that's the case, just return * without doing anything. */ if (!user_mode(regs)) return; if (get_signal(&ksig)) { /* Whee! Actually deliver the signal. */ handle_signal(canrestart, &ksig, regs); return; } /* Got here from a system call? */ if (canrestart) { /* Restart the system call - no handlers present. */ if (regs->r10 == -ERESTARTNOHAND || regs->r10 == -ERESTARTSYS || regs->r10 == -ERESTARTNOINTR) { RESTART_CRIS_SYS(regs); } if (regs->r10 == -ERESTART_RESTARTBLOCK){ regs->r9 = __NR_restart_syscall; regs->erp -= 2; } } /* if there's no signal to deliver, we just put the saved sigmask * back */ restore_saved_sigmask(); }

Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik9775.19%116.67%
Rabin Vincent1511.63%116.67%
Jesper Nilsson86.20%233.33%
Richard Weinberger75.43%116.67%
Al Viro21.55%116.67%
Total129100.00%6100.00%


asmlinkage void ugdb_trap_user(struct thread_info *ti, int sig) { if (((user_regs(ti)->exs & 0xff00) >> 8) != SINGLE_STEP_INTR_VECT) { /* Zero single-step PC if the reason we stopped wasn't a single step exception. This is to avoid relying on it when it isn't reliable. */ user_regs(ti)->spc = 0; } /* FIXME: Filter out false h/w breakpoint hits (i.e. EDA not within any configured h/w breakpoint range). Synchronize with what already exists for kernel debugging. */ if (((user_regs(ti)->exs & 0xff00) >> 8) == BREAK_8_INTR_VECT) { /* Break 8: subtract 2 from ERP unless in a delay slot. */ if (!(user_regs(ti)->erp & 0x1)) user_regs(ti)->erp -= 2; } sys_kill(ti->task->pid, sig); }

Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik10199.02%150.00%
Lucas De Marchi10.98%150.00%
Total102100.00%2100.00%


void keep_debug_flags(unsigned long oldccs, unsigned long oldspc, struct pt_regs *regs) { if (oldccs & (1 << Q_CCS_BITNR)) { /* Pending single step due to single-stepping the break 13 in the signal trampoline: keep the Q flag. */ regs->ccs |= (1 << Q_CCS_BITNR); /* S flag should be set - complain if it's not. */ if (!(oldccs & (1 << (S_CCS_BITNR + CCS_SHIFT)))) { printk("Q flag but no S flag?"); } regs->ccs |= (1 << (S_CCS_BITNR + CCS_SHIFT)); /* Assume the SPC is valid and interesting. */ regs->spc = oldspc; } else if (oldccs & (1 << (S_CCS_BITNR + CCS_SHIFT))) { /* If a h/w bp was set in the signal handler we need to keep the S flag. */ regs->ccs |= (1 << (S_CCS_BITNR + CCS_SHIFT)); /* Don't keep the old SPC though; if we got here due to a single-step, the Q flag should have been set. */ } else if (regs->spc) { /* If we were single-stepping *before* the signal was taken, we don't want to restore that state now, because GDB will have forgotten all about it. */ regs->spc = 0; regs->ccs &= ~(1 << (S_CCS_BITNR + CCS_SHIFT)); } }

Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik151100.00%1100.00%
Total151100.00%1100.00%

/* Set up the trampolines on the signal return page. */
int __init cris_init_signal(void) { u16* data = kmalloc(PAGE_SIZE, GFP_KERNEL); /* This is movu.w __NR_sigreturn, r9; break 13; */ data[0] = 0x9c5f; data[1] = __NR_sigreturn; data[2] = 0xe93d; /* This is movu.w __NR_rt_sigreturn, r9; break 13; */ data[3] = 0x9c5f; data[4] = __NR_rt_sigreturn; data[5] = 0xe93d; /* Map to userspace with appropriate permissions (no write access...) */ cris_signal_return_page = (unsigned long) __ioremap_prot(virt_to_phys(data), PAGE_SIZE, PAGE_SIGNAL_TRAMPOLINE); return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik85100.00%1100.00%
Total85100.00%1100.00%

__initcall(cris_init_signal);

Overall Contributors

PersonTokensPropCommitsCommitProp
Mikael Starvik183590.31%14.35%
Richard Weinberger914.48%28.70%
Al Viro422.07%730.43%
Jesper Nilsson271.33%313.04%
Rabin Vincent231.13%14.35%
Tejun Heo30.15%14.35%
Ingo Molnar30.15%14.35%
Matt Fleming20.10%14.35%
Linus Torvalds10.05%14.35%
Frederik Schwarzer10.05%14.35%
Lucas De Marchi10.05%14.35%
Adrian Bunk10.05%14.35%
Andrew Lutomirski10.05%14.35%
Greg Kroah-Hartman10.05%14.35%
Total2032100.00%23100.00%
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