// SPDX-License-Identifier: GPL-2.0 /* * Copyright (C) 1991, 1992 Linus Torvalds * Copyright (C) 2000, 2001, 2002 Andi Kleen SuSE Labs * * 1997-11-28 Modified for POSIX.1b signals by Richard Henderson * 2000-06-20 Pentium III FXSR, SSE support by Gareth Hughes * 2000-2002 x86-64 support by Andi Kleen */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include <linux/sched.h> #include <linux/sched/task_stack.h> #include <linux/mm.h> #include <linux/smp.h> #include <linux/kernel.h> #include <linux/kstrtox.h> #include <linux/errno.h> #include <linux/wait.h> #include <linux/unistd.h> #include <linux/stddef.h> #include <linux/personality.h> #include <linux/uaccess.h> #include <linux/user-return-notifier.h> #include <linux/uprobes.h> #include <linux/context_tracking.h> #include <linux/entry-common.h> #include <linux/syscalls.h> #include <asm/processor.h> #include <asm/ucontext.h> #include <asm/fpu/signal.h> #include <asm/fpu/xstate.h> #include <asm/vdso.h> #include <asm/mce.h> #include <asm/sighandling.h> #include <asm/vm86.h> #include <asm/syscall.h> #include <asm/sigframe.h> #include <asm/signal.h> static inline int is_ia32_compat_frame(struct ksignal *ksig) { return IS_ENABLED(CONFIG_IA32_EMULATION) && ksig->ka.sa.sa_flags & SA_IA32_ABI; } static inline int is_ia32_frame(struct ksignal *ksig) { return IS_ENABLED(CONFIG_X86_32) || is_ia32_compat_frame(ksig); } static inline int is_x32_frame(struct ksignal *ksig) { return IS_ENABLED(CONFIG_X86_X32_ABI) && ksig->ka.sa.sa_flags & SA_X32_ABI; } /* * Set up a signal frame. */ /* x86 ABI requires 16-byte alignment */ #define FRAME_ALIGNMENT 16UL #define MAX_FRAME_PADDING (FRAME_ALIGNMENT - 1) /* * Determine which stack to use.. */ void __user * get_sigframe(struct ksignal *ksig, struct pt_regs *regs, size_t frame_size, void __user **fpstate) { struct k_sigaction *ka = &ksig->ka; int ia32_frame = is_ia32_frame(ksig); /* Default to using normal stack */ bool nested_altstack = on_sig_stack(regs->sp); bool entering_altstack = false; unsigned long math_size = 0; unsigned long sp = regs->sp; unsigned long buf_fx = 0; /* redzone */ if (!ia32_frame) sp -= 128; /* This is the X/Open sanctioned signal stack switching. */ if (ka->sa.sa_flags & SA_ONSTACK) { /* * This checks nested_altstack via sas_ss_flags(). Sensible * programs use SS_AUTODISARM, which disables that check, and * programs that don't use SS_AUTODISARM get compatible. */ if (sas_ss_flags(sp) == 0) { sp = current->sas_ss_sp + current->sas_ss_size; entering_altstack = true; } } else if (ia32_frame && !nested_altstack && regs->ss != __USER_DS && !(ka->sa.sa_flags & SA_RESTORER) && ka->sa.sa_restorer) { /* This is the legacy signal stack switching. */ sp = (unsigned long) ka->sa.sa_restorer; entering_altstack = true; } sp = fpu__alloc_mathframe(sp, ia32_frame, &buf_fx, &math_size); *fpstate = (void __user *)sp; sp -= frame_size; if (ia32_frame) /* * Align the stack pointer according to the i386 ABI, * i.e. so that on function entry ((sp + 4) & 15) == 0. */ sp = ((sp + 4) & -FRAME_ALIGNMENT) - 4; else sp = round_down(sp, FRAME_ALIGNMENT) - 8; /* * If we are on the alternate signal stack and would overflow it, don't. * Return an always-bogus address instead so we will die with SIGSEGV. */ if (unlikely((nested_altstack || entering_altstack) && !__on_sig_stack(sp))) { if (show_unhandled_signals && printk_ratelimit()) pr_info("%s[%d] overflowed sigaltstack\n", current->comm, task_pid_nr(current)); return (void __user *)-1L; } /* save i387 and extended state */ if (!copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size)) return (void __user *)-1L; return (void __user *)sp; } /* * There are four different struct types for signal frame: sigframe_ia32, * rt_sigframe_ia32, rt_sigframe_x32, and rt_sigframe. Use the worst case * -- the largest size. It means the size for 64-bit apps is a bit more * than needed, but this keeps the code simple. */ #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) # define MAX_FRAME_SIGINFO_UCTXT_SIZE sizeof(struct sigframe_ia32) #else # define MAX_FRAME_SIGINFO_UCTXT_SIZE sizeof(struct rt_sigframe) #endif /* * The FP state frame contains an XSAVE buffer which must be 64-byte aligned. * If a signal frame starts at an unaligned address, extra space is required. * This is the max alignment padding, conservatively. */ #define MAX_XSAVE_PADDING 63UL /* * The frame data is composed of the following areas and laid out as: * * ------------------------- * | alignment padding | * ------------------------- * | (f)xsave frame | * ------------------------- * | fsave header | * ------------------------- * | alignment padding | * ------------------------- * | siginfo + ucontext | * ------------------------- */ /* max_frame_size tells userspace the worst case signal stack size. */ static unsigned long __ro_after_init max_frame_size; static unsigned int __ro_after_init fpu_default_state_size; static int __init init_sigframe_size(void) { fpu_default_state_size = fpu__get_fpstate_size(); max_frame_size = MAX_FRAME_SIGINFO_UCTXT_SIZE + MAX_FRAME_PADDING; max_frame_size += fpu_default_state_size + MAX_XSAVE_PADDING; /* Userspace expects an aligned size. */ max_frame_size = round_up(max_frame_size, FRAME_ALIGNMENT); pr_info("max sigframe size: %lu\n", max_frame_size); return 0; } early_initcall(init_sigframe_size); unsigned long get_sigframe_size(void) { return max_frame_size; } static int setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs) { /* Perform fixup for the pre-signal frame. */ rseq_signal_deliver(ksig, regs); /* Set up the stack frame */ if (is_ia32_frame(ksig)) { if (ksig->ka.sa.sa_flags & SA_SIGINFO) return ia32_setup_rt_frame(ksig, regs); else return ia32_setup_frame(ksig, regs); } else if (is_x32_frame(ksig)) { return x32_setup_rt_frame(ksig, regs); } else { return x64_setup_rt_frame(ksig, regs); } } static void handle_signal(struct ksignal *ksig, struct pt_regs *regs) { bool stepping, failed; struct fpu *fpu = ¤t->thread.fpu; if (v8086_mode(regs)) save_v86_state((struct kernel_vm86_regs *) regs, VM86_SIGNAL); /* Are we from a system call? */ if (syscall_get_nr(current, regs) != -1) { /* If so, check system call restarting.. */ switch (syscall_get_error(current, regs)) { case -ERESTART_RESTARTBLOCK: case -ERESTARTNOHAND: regs->ax = -EINTR; break; case -ERESTARTSYS: if (!(ksig->ka.sa.sa_flags & SA_RESTART)) { regs->ax = -EINTR; break; } fallthrough; case -ERESTARTNOINTR: regs->ax = regs->orig_ax; regs->ip -= 2; break; } } /* * If TF is set due to a debugger (TIF_FORCED_TF), clear TF now * so that register information in the sigcontext is correct and * then notify the tracer before entering the signal handler. */ stepping = test_thread_flag(TIF_SINGLESTEP); if (stepping) user_disable_single_step(current); failed = (setup_rt_frame(ksig, regs) < 0); if (!failed) { /* * Clear the direction flag as per the ABI for function entry. * * Clear RF when entering the signal handler, because * it might disable possible debug exception from the * signal handler. * * Clear TF for the case when it wasn't set by debugger to * avoid the recursive send_sigtrap() in SIGTRAP handler. */ regs->flags &= ~(X86_EFLAGS_DF|X86_EFLAGS_RF|X86_EFLAGS_TF); /* * Ensure the signal handler starts with the new fpu state. */ fpu__clear_user_states(fpu); } signal_setup_done(failed, ksig, stepping); } static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs) { #ifdef CONFIG_IA32_EMULATION if (current->restart_block.arch_data & TS_COMPAT) return __NR_ia32_restart_syscall; #endif #ifdef CONFIG_X86_X32_ABI return __NR_restart_syscall | (regs->orig_ax & __X32_SYSCALL_BIT); #else return __NR_restart_syscall; #endif } /* * 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. */ void arch_do_signal_or_restart(struct pt_regs *regs) { struct ksignal ksig; if (get_signal(&ksig)) { /* Whee! Actually deliver the signal. */ handle_signal(&ksig, regs); return; } /* Did we come from a system call? */ if (syscall_get_nr(current, regs) != -1) { /* Restart the system call - no handlers present */ switch (syscall_get_error(current, regs)) { case -ERESTARTNOHAND: case -ERESTARTSYS: case -ERESTARTNOINTR: regs->ax = regs->orig_ax; regs->ip -= 2; break; case -ERESTART_RESTARTBLOCK: regs->ax = get_nr_restart_syscall(regs); regs->ip -= 2; break; } } /* * If there's no signal to deliver, we just put the saved sigmask * back. */ restore_saved_sigmask(); } void signal_fault(struct pt_regs *regs, void __user *frame, char *where) { struct task_struct *me = current; if (show_unhandled_signals && printk_ratelimit()) { printk("%s" "%s[%d] bad frame in %s frame:%p ip:%lx sp:%lx orax:%lx", task_pid_nr(current) > 1 ? KERN_INFO : KERN_EMERG, me->comm, me->pid, where, frame, regs->ip, regs->sp, regs->orig_ax); print_vma_addr(KERN_CONT " in ", regs->ip); pr_cont("\n"); } force_sig(SIGSEGV); } #ifdef CONFIG_DYNAMIC_SIGFRAME #ifdef CONFIG_STRICT_SIGALTSTACK_SIZE static bool strict_sigaltstack_size __ro_after_init = true; #else static bool strict_sigaltstack_size __ro_after_init = false; #endif static int __init strict_sas_size(char *arg) { return kstrtobool(arg, &strict_sigaltstack_size) == 0; } __setup("strict_sas_size", strict_sas_size); /* * MINSIGSTKSZ is 2048 and can't be changed despite the fact that AVX512 * exceeds that size already. As such programs might never use the * sigaltstack they just continued to work. While always checking against * the real size would be correct, this might be considered a regression. * * Therefore avoid the sanity check, unless enforced by kernel * configuration or command line option. * * When dynamic FPU features are supported, the check is also enforced when * the task has permissions to use dynamic features. Tasks which have no * permission are checked against the size of the non-dynamic feature set * if strict checking is enabled. This avoids forcing all tasks on the * system to allocate large sigaltstacks even if they are never going * to use a dynamic feature. As this is serialized via sighand::siglock * any permission request for a dynamic feature either happened already * or will see the newly install sigaltstack size in the permission checks. */ bool sigaltstack_size_valid(size_t ss_size) { unsigned long fsize = max_frame_size - fpu_default_state_size; u64 mask; lockdep_assert_held(¤t->sighand->siglock); if (!fpu_state_size_dynamic() && !strict_sigaltstack_size) return true; fsize += current->group_leader->thread.fpu.perm.__user_state_size; if (likely(ss_size > fsize)) return true; if (strict_sigaltstack_size) return ss_size > fsize; mask = current->group_leader->thread.fpu.perm.__state_perm; if (mask & XFEATURE_MASK_USER_DYNAMIC) return ss_size > fsize; return true; } #endif /* CONFIG_DYNAMIC_SIGFRAME */