add new system file

hc

2024-02-20 102a0743326a03cd1a1202ceda21e175b7d3575c

 kernel/arch/arm64/kernel/syscall.c
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@@ -50,10 +50,7 @@
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 		ret = do_ni_syscall(regs, scno);
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 	}
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-	if (is_compat_task())
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-		ret = lower_32_bits(ret);
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-
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-	regs->regs[0] = ret;
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+	syscall_set_return_value(current, regs, 0, ret);
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 }
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 static inline bool has_syscall_work(unsigned long flags)
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@@ -101,14 +98,55 @@
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 	regs->orig_x0 = regs->regs[0];
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 	regs->syscallno = scno;
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+	/*
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+	 * BTI note:
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+	 * The architecture does not guarantee that SPSR.BTYPE is zero
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+	 * on taking an SVC, so we could return to userspace with a
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+	 * non-zero BTYPE after the syscall.
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+	 *
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+	 * This shouldn't matter except when userspace is explicitly
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+	 * doing something stupid, such as setting PROT_BTI on a page
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+	 * that lacks conforming BTI/PACIxSP instructions, falling
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+	 * through from one executable page to another with differing
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+	 * PROT_BTI, or messing with BTYPE via ptrace: in such cases,
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+	 * userspace should not be surprised if a SIGILL occurs on
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+	 * syscall return.
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+	 *
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+	 * So, don't touch regs->pstate & PSR_BTYPE_MASK here.
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+	 * (Similarly for HVC and SMC elsewhere.)
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+	 */
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+
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 	cortex_a76_erratum_1463225_svc_handler();
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-	user_exit_irqoff();
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 	local_daif_restore(DAIF_PROCCTX);
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+	if (flags & _TIF_MTE_ASYNC_FAULT) {
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+		/*
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+		 * Process the asynchronous tag check fault before the actual
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+		 * syscall. do_notify_resume() will send a signal to userspace
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+		 * before the syscall is restarted.
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+		 */
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+		syscall_set_return_value(current, regs, -ERESTARTNOINTR, 0);
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+		return;
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+	}
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+
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 	if (has_syscall_work(flags)) {
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-		/* set default errno for user-issued syscall(-1) */
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+		/*
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+		 * The de-facto standard way to skip a system call using ptrace
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+		 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a
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+		 * suitable error code for consumption by userspace. However,
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+		 * this cannot be distinguished from a user-issued syscall(-1)
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+		 * and so we must set x0 to -ENOSYS here in case the tracer doesn't
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+		 * issue the skip and we fall into trace_exit with x0 preserved.
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+		 *
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+		 * This is slightly odd because it also means that if a tracer
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+		 * sets the system call number to -1 but does not initialise x0,
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+		 * then x0 will be preserved for all system calls apart from a
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+		 * user-issued syscall(-1). However, requesting a skip and not
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+		 * setting the return value is unlikely to do anything sensible
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+		 * anyway.
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+		 */
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 		if (scno == NO_SYSCALL)
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-			regs->regs[0] = -ENOSYS;
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+			syscall_set_return_value(current, regs, -ENOSYS, 0);
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 		scno = syscall_trace_enter(regs);
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 		if (scno == NO_SYSCALL)
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 			goto trace_exit;
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@@ -124,15 +162,8 @@
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 	if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
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 		local_daif_mask();
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 		flags = current_thread_info()->flags;
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-		if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP)) {
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-			/*
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-			 * We're off to userspace, where interrupts are
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-			 * always enabled after we restore the flags from
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-			 * the SPSR.
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-			 */
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-			trace_hardirqs_on();
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+		if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP))
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 			return;
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-		}
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 		local_daif_restore(DAIF_PROCCTX);
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 	}
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@@ -157,14 +188,14 @@
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 	sve_user_disable();
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 }
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-asmlinkage void el0_svc_handler(struct pt_regs *regs)
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+void do_el0_svc(struct pt_regs *regs)
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 {
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 	sve_user_discard();
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 	el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);
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 }
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 #ifdef CONFIG_COMPAT
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-asmlinkage void el0_svc_compat_handler(struct pt_regs *regs)
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+void do_el0_svc_compat(struct pt_regs *regs)
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 {
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 	el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls,
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 		       compat_sys_call_table);