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2024-10-22 8ac6c7a54ed1b98d142dce24b11c6de6a1e239a5 
 kernel/tools/testing/selftests/x86/single_step_syscall.c
....@@ -1,15 +1,7 @@
1
+// SPDX-License-Identifier: GPL-2.0-only
12 /*
23  * single_step_syscall.c - single-steps various x86 syscalls
34  * Copyright (c) 2014-2015 Andrew Lutomirski
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- *
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- * This program is free software; you can redistribute it and/or modify
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- * it under the terms and conditions of the GNU General Public License,
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- * version 2, as published by the Free Software Foundation.
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- *
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- * This program is distributed in the hope it will be useful, but
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- * WITHOUT ANY WARRANTY; without even the implied warranty of
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- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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- * General Public License for more details.
135  *
146  * This is a very simple series of tests that makes system calls with
157  * the TF flag set.  This exercises some nasty kernel code in the
....@@ -39,6 +31,8 @@
3931 #include <sys/ptrace.h>
4032 #include <sys/user.h>
4133 
34
+#include "helpers.h"
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+
4236 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
4337 		       int flags)
4438 {
....@@ -51,7 +45,19 @@
5145 		err(1, "sigaction");
5246 }
5347 
54
-static volatile sig_atomic_t sig_traps;
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+static void clearhandler(int sig)
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+{
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+	struct sigaction sa;
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+	memset(&sa, 0, sizeof(sa));
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+	sa.sa_handler = SIG_DFL;
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+	sigemptyset(&sa.sa_mask);
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+	if (sigaction(sig, &sa, 0))
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+		err(1, "sigaction");
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+}
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+
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+static volatile sig_atomic_t sig_traps, sig_eflags;
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+sigjmp_buf jmpbuf;
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+static unsigned char altstack_data[SIGSTKSZ];
5561 
5662 #ifdef __x86_64__
5763 # define REG_IP REG_RIP
....@@ -62,21 +68,6 @@
6268 # define WIDTH "l"
6369 # define INT80_CLOBBERS
6470 #endif
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-
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-static unsigned long get_eflags(void)
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-{
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-	unsigned long eflags;
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-	asm volatile ("pushf" WIDTH "\n\tpop" WIDTH " %0" : "=rm" (eflags));
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-	return eflags;
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-}
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-
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-static void set_eflags(unsigned long eflags)
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-{
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-	asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
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-		      : : "rm" (eflags) : "flags");
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-}
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-
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-#define X86_EFLAGS_TF (1UL << 8)
8071 
8172 static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
8273 {
....@@ -98,6 +89,25 @@
9889 	}
9990 }
10091 
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+static char const * const signames[] = {
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+	[SIGSEGV] = "SIGSEGV",
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+	[SIGBUS] = "SIBGUS",
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+	[SIGTRAP] = "SIGTRAP",
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+	[SIGILL] = "SIGILL",
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+};
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+
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+static void print_and_longjmp(int sig, siginfo_t *si, void *ctx_void)
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+{
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+	ucontext_t *ctx = ctx_void;
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+
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+	printf("\tGot %s with RIP=%lx, TF=%ld\n", signames[sig],
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+	       (unsigned long)ctx->uc_mcontext.gregs[REG_IP],
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+	       (unsigned long)ctx->uc_mcontext.gregs[REG_EFL] & X86_EFLAGS_TF);
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+
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+	sig_eflags = (unsigned long)ctx->uc_mcontext.gregs[REG_EFL];
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+	siglongjmp(jmpbuf, 1);
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+}
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+
101111 static void check_result(void)
102112 {
103113 	unsigned long new_eflags = get_eflags();
....@@ -115,6 +125,22 @@
115125 
116126 	printf("[OK]\tSurvived with TF set and %d traps\n", (int)sig_traps);
117127 	sig_traps = 0;
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+}
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+
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+static void fast_syscall_no_tf(void)
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+{
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+	sig_traps = 0;
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+	printf("[RUN]\tFast syscall with TF cleared\n");
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+	fflush(stdout);  /* Force a syscall */
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+	if (get_eflags() & X86_EFLAGS_TF) {
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+		printf("[FAIL]\tTF is now set\n");
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+		exit(1);
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+	}
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+	if (sig_traps) {
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+		printf("[FAIL]\tGot SIGTRAP\n");
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+		exit(1);
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+	}
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+	printf("[OK]\tNothing unexpected happened\n");
118144 }
119145 
120146 int main()
....@@ -171,17 +197,46 @@
171197 	check_result();
172198 
173199 	/* Now make sure that another fast syscall doesn't set TF again. */
174
-	printf("[RUN]\tFast syscall with TF cleared\n");
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-	fflush(stdout);  /* Force a syscall */
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-	if (get_eflags() & X86_EFLAGS_TF) {
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-		printf("[FAIL]\tTF is now set\n");
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+	fast_syscall_no_tf();
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+
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+	/*
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+	 * And do a forced SYSENTER to make sure that this works even if
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+	 * fast syscalls don't use SYSENTER.
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+	 *
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+	 * Invoking SYSENTER directly breaks all the rules.  Just handle
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+	 * the SIGSEGV.
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+	 */
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+	if (sigsetjmp(jmpbuf, 1) == 0) {
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+		unsigned long nr = SYS_getpid;
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+		printf("[RUN]\tSet TF and check SYSENTER\n");
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+		stack_t stack = {
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+			.ss_sp = altstack_data,
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+			.ss_size = SIGSTKSZ,
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+		};
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+		if (sigaltstack(&stack, NULL) != 0)
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+			err(1, "sigaltstack");
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+		sethandler(SIGSEGV, print_and_longjmp,
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+			   SA_RESETHAND | SA_ONSTACK);
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+		sethandler(SIGILL, print_and_longjmp, SA_RESETHAND);
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+		set_eflags(get_eflags() | X86_EFLAGS_TF);
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+		/* Clear EBP first to make sure we segfault cleanly. */
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+		asm volatile ("xorl %%ebp, %%ebp; SYSENTER" : "+a" (nr) :: "flags", "rcx"
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+#ifdef __x86_64__
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+				, "r11"
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+#endif
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+			);
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+
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+		/* We're unreachable here.  SYSENTER forgets RIP. */
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+	}
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+	clearhandler(SIGSEGV);
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+	clearhandler(SIGILL);
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+	if (!(sig_eflags & X86_EFLAGS_TF)) {
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+		printf("[FAIL]\tTF was cleared\n");
178235 		exit(1);
179236 	}
180
-	if (sig_traps) {
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-		printf("[FAIL]\tGot SIGTRAP\n");
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-		exit(1);
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-	}
184
-	printf("[OK]\tNothing unexpected happened\n");
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+
238
+	/* Now make sure that another fast syscall doesn't set TF again. */
239
+	fast_syscall_no_tf();
185240 
186241 	return 0;
187242 }