| // SPDX-License-Identifier: GPL-2.0 |
| |
| #include <linux/compiler.h> |
| #include <linux/context_tracking.h> |
| #include <linux/errno.h> |
| #include <linux/nospec.h> |
| #include <linux/ptrace.h> |
| #include <linux/randomize_kstack.h> |
| #include <linux/syscalls.h> |
| |
| #include <asm/daifflags.h> |
| #include <asm/debug-monitors.h> |
| #include <asm/exception.h> |
| #include <asm/fpsimd.h> |
| #include <asm/syscall.h> |
| #include <asm/thread_info.h> |
| #include <asm/unistd.h> |
| |
| long compat_arm_syscall(struct pt_regs *regs, int scno); |
| long sys_ni_syscall(void); |
| |
| static long do_ni_syscall(struct pt_regs *regs, int scno) |
| { |
| #ifdef CONFIG_COMPAT |
| long ret; |
| if (is_compat_task()) { |
| ret = compat_arm_syscall(regs, scno); |
| if (ret != -ENOSYS) |
| return ret; |
| } |
| #endif |
| |
| return sys_ni_syscall(); |
| } |
| |
| static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn) |
| { |
| return syscall_fn(regs); |
| } |
| |
| static void invoke_syscall(struct pt_regs *regs, unsigned int scno, |
| unsigned int sc_nr, |
| const syscall_fn_t syscall_table[]) |
| { |
| long ret; |
| |
| add_random_kstack_offset(); |
| |
| if (scno < sc_nr) { |
| syscall_fn_t syscall_fn; |
| syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)]; |
| ret = __invoke_syscall(regs, syscall_fn); |
| } else { |
| ret = do_ni_syscall(regs, scno); |
| } |
| |
| syscall_set_return_value(current, regs, 0, ret); |
| |
| /* |
| * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), |
| * but not enough for arm64 stack utilization comfort. To keep |
| * reasonable stack head room, reduce the maximum offset to 9 bits. |
| * |
| * The actual entropy will be further reduced by the compiler when |
| * applying stack alignment constraints: the AAPCS mandates a |
| * 16-byte (i.e. 4-bit) aligned SP at function boundaries. |
| * |
| * The resulting 5 bits of entropy is seen in SP[8:4]. |
| */ |
| choose_random_kstack_offset(get_random_int() & 0x1FF); |
| } |
| |
| static inline bool has_syscall_work(unsigned long flags) |
| { |
| return unlikely(flags & _TIF_SYSCALL_WORK); |
| } |
| |
| int syscall_trace_enter(struct pt_regs *regs); |
| void syscall_trace_exit(struct pt_regs *regs); |
| |
| static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, |
| const syscall_fn_t syscall_table[]) |
| { |
| unsigned long flags = read_thread_flags(); |
| |
| regs->orig_x0 = regs->regs[0]; |
| regs->syscallno = scno; |
| |
| /* |
| * BTI note: |
| * The architecture does not guarantee that SPSR.BTYPE is zero |
| * on taking an SVC, so we could return to userspace with a |
| * non-zero BTYPE after the syscall. |
| * |
| * This shouldn't matter except when userspace is explicitly |
| * doing something stupid, such as setting PROT_BTI on a page |
| * that lacks conforming BTI/PACIxSP instructions, falling |
| * through from one executable page to another with differing |
| * PROT_BTI, or messing with BTYPE via ptrace: in such cases, |
| * userspace should not be surprised if a SIGILL occurs on |
| * syscall return. |
| * |
| * So, don't touch regs->pstate & PSR_BTYPE_MASK here. |
| * (Similarly for HVC and SMC elsewhere.) |
| */ |
| |
| local_daif_restore(DAIF_PROCCTX); |
| |
| if (flags & _TIF_MTE_ASYNC_FAULT) { |
| /* |
| * Process the asynchronous tag check fault before the actual |
| * syscall. do_notify_resume() will send a signal to userspace |
| * before the syscall is restarted. |
| */ |
| syscall_set_return_value(current, regs, -ERESTARTNOINTR, 0); |
| return; |
| } |
| |
| if (has_syscall_work(flags)) { |
| /* |
| * The de-facto standard way to skip a system call using ptrace |
| * is to set the system call to -1 (NO_SYSCALL) and set x0 to a |
| * suitable error code for consumption by userspace. However, |
| * this cannot be distinguished from a user-issued syscall(-1) |
| * and so we must set x0 to -ENOSYS here in case the tracer doesn't |
| * issue the skip and we fall into trace_exit with x0 preserved. |
| * |
| * This is slightly odd because it also means that if a tracer |
| * sets the system call number to -1 but does not initialise x0, |
| * then x0 will be preserved for all system calls apart from a |
| * user-issued syscall(-1). However, requesting a skip and not |
| * setting the return value is unlikely to do anything sensible |
| * anyway. |
| */ |
| if (scno == NO_SYSCALL) |
| syscall_set_return_value(current, regs, -ENOSYS, 0); |
| scno = syscall_trace_enter(regs); |
| if (scno == NO_SYSCALL) |
| goto trace_exit; |
| } |
| |
| invoke_syscall(regs, scno, sc_nr, syscall_table); |
| |
| /* |
| * The tracing status may have changed under our feet, so we have to |
| * check again. However, if we were tracing entry, then we always trace |
| * exit regardless, as the old entry assembly did. |
| */ |
| if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) { |
| local_daif_mask(); |
| flags = read_thread_flags(); |
| if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP)) |
| return; |
| local_daif_restore(DAIF_PROCCTX); |
| } |
| |
| trace_exit: |
| syscall_trace_exit(regs); |
| } |
| |
| /* |
| * As per the ABI exit SME streaming mode and clear the SVE state not |
| * shared with FPSIMD on syscall entry. |
| */ |
| static inline void fp_user_discard(void) |
| { |
| /* |
| * If SME is active then exit streaming mode. If ZA is active |
| * then flush the SVE registers but leave userspace access to |
| * both SVE and SME enabled, otherwise disable SME for the |
| * task and fall through to disabling SVE too. This means |
| * that after a syscall we never have any streaming mode |
| * register state to track, if this changes the KVM code will |
| * need updating. |
| */ |
| if (system_supports_sme() && test_thread_flag(TIF_SME)) { |
| u64 svcr = read_sysreg_s(SYS_SVCR); |
| |
| if (svcr & SVCR_SM_MASK) |
| sme_smstop_sm(); |
| } |
| |
| if (!system_supports_sve()) |
| return; |
| |
| /* |
| * If SME is not active then disable SVE, the registers will |
| * be cleared when userspace next attempts to access them and |
| * we do not need to track the SVE register state until then. |
| */ |
| clear_thread_flag(TIF_SVE); |
| |
| /* |
| * task_fpsimd_load() won't be called to update CPACR_EL1 in |
| * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only |
| * happens if a context switch or kernel_neon_begin() or context |
| * modification (sigreturn, ptrace) intervenes. |
| * So, ensure that CPACR_EL1 is already correct for the fast-path case. |
| */ |
| sve_user_disable(); |
| } |
| |
| void do_el0_svc(struct pt_regs *regs) |
| { |
| fp_user_discard(); |
| el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table); |
| } |
| |
| #ifdef CONFIG_COMPAT |
| void do_el0_svc_compat(struct pt_regs *regs) |
| { |
| el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls, |
| compat_sys_call_table); |
| } |
| #endif |