1 files changed, 242 insertions, 0 deletions
diff --git a/tools/testing/selftests/x86/single_step_syscall.c b/tools/testing/selftests/x86/single_step_syscall.c
new file mode 100644
index 000000000..9a30f443e
--- /dev/null
+++ b/tools/testing/selftests/x86/single_step_syscall.c
@@ -0,0 +1,242 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * single_step_syscall.c - single-steps various x86 syscalls
+ * Copyright (c) 2014-2015 Andrew Lutomirski
+ *
+ * This is a very simple series of tests that makes system calls with
+ * the TF flag set.  This exercises some nasty kernel code in the
+ * SYSENTER case: SYSENTER does not clear TF, so SYSENTER with TF set
+ * immediately issues #DB from CPL 0.  This requires special handling in
+ * the kernel.
+ */
+
+#define _GNU_SOURCE
+
+#include <sys/time.h>
+#include <time.h>
+#include <stdlib.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include <inttypes.h>
+#include <sys/mman.h>
+#include <sys/signal.h>
+#include <sys/ucontext.h>
+#include <asm/ldt.h>
+#include <err.h>
+#include <setjmp.h>
+#include <stddef.h>
+#include <stdbool.h>
+#include <sys/ptrace.h>
+#include <sys/user.h>
+
+#include "helpers.h"
+
+static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
+		       int flags)
+{
+	struct sigaction sa;
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_sigaction = handler;
+	sa.sa_flags = SA_SIGINFO | flags;
+	sigemptyset(&sa.sa_mask);
+	if (sigaction(sig, &sa, 0))
+		err(1, "sigaction");
+}
+
+static void clearhandler(int sig)
+{
+	struct sigaction sa;
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_handler = SIG_DFL;
+	sigemptyset(&sa.sa_mask);
+	if (sigaction(sig, &sa, 0))
+		err(1, "sigaction");
+}
+
+static volatile sig_atomic_t sig_traps, sig_eflags;
+sigjmp_buf jmpbuf;
+
+#ifdef __x86_64__
+# define REG_IP REG_RIP
+# define WIDTH "q"
+# define INT80_CLOBBERS "r8", "r9", "r10", "r11"
+#else
+# define REG_IP REG_EIP
+# define WIDTH "l"
+# define INT80_CLOBBERS
+#endif
+
+static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
+{
+	ucontext_t *ctx = (ucontext_t*)ctx_void;
+
+	if (get_eflags() & X86_EFLAGS_TF) {
+		set_eflags(get_eflags() & ~X86_EFLAGS_TF);
+		printf("[WARN]\tSIGTRAP handler had TF set\n");
+		_exit(1);
+	}
+
+	sig_traps++;
+
+	if (sig_traps == 10000 || sig_traps == 10001) {
+		printf("[WARN]\tHit %d SIGTRAPs with si_addr 0x%lx, ip 0x%lx\n",
+		       (int)sig_traps,
+		       (unsigned long)info->si_addr,
+		       (unsigned long)ctx->uc_mcontext.gregs[REG_IP]);
+	}
+}
+
+static char const * const signames[] = {
+	[SIGSEGV] = "SIGSEGV",
+	[SIGBUS] = "SIBGUS",
+	[SIGTRAP] = "SIGTRAP",
+	[SIGILL] = "SIGILL",
+};
+
+static void print_and_longjmp(int sig, siginfo_t *si, void *ctx_void)
+{
+	ucontext_t *ctx = ctx_void;
+
+	printf("\tGot %s with RIP=%lx, TF=%ld\n", signames[sig],
+	       (unsigned long)ctx->uc_mcontext.gregs[REG_IP],
+	       (unsigned long)ctx->uc_mcontext.gregs[REG_EFL] & X86_EFLAGS_TF);
+
+	sig_eflags = (unsigned long)ctx->uc_mcontext.gregs[REG_EFL];
+	siglongjmp(jmpbuf, 1);
+}
+
+static void check_result(void)
+{
+	unsigned long new_eflags = get_eflags();
+	set_eflags(new_eflags & ~X86_EFLAGS_TF);
+
+	if (!sig_traps) {
+		printf("[FAIL]\tNo SIGTRAP\n");
+		exit(1);
+	}
+
+	if (!(new_eflags & X86_EFLAGS_TF)) {
+		printf("[FAIL]\tTF was cleared\n");
+		exit(1);
+	}
+
+	printf("[OK]\tSurvived with TF set and %d traps\n", (int)sig_traps);
+	sig_traps = 0;
+}
+
+static void fast_syscall_no_tf(void)
+{
+	sig_traps = 0;
+	printf("[RUN]\tFast syscall with TF cleared\n");
+	fflush(stdout);  /* Force a syscall */
+	if (get_eflags() & X86_EFLAGS_TF) {
+		printf("[FAIL]\tTF is now set\n");
+		exit(1);
+	}
+	if (sig_traps) {
+		printf("[FAIL]\tGot SIGTRAP\n");
+		exit(1);
+	}
+	printf("[OK]\tNothing unexpected happened\n");
+}
+
+int main()
+{
+#ifdef CAN_BUILD_32
+	int tmp;
+#endif
+
+	sethandler(SIGTRAP, sigtrap, 0);
+
+	printf("[RUN]\tSet TF and check nop\n");
+	set_eflags(get_eflags() | X86_EFLAGS_TF);
+	asm volatile ("nop");
+	check_result();
+
+#ifdef __x86_64__
+	printf("[RUN]\tSet TF and check syscall-less opportunistic sysret\n");
+	set_eflags(get_eflags() | X86_EFLAGS_TF);
+	extern unsigned char post_nop[];
+	asm volatile ("pushf" WIDTH "\n\t"
+		      "pop" WIDTH " %%r11\n\t"
+		      "nop\n\t"
+		      "post_nop:"
+		      : : "c" (post_nop) : "r11");
+	check_result();
+#endif
+#ifdef CAN_BUILD_32
+	printf("[RUN]\tSet TF and check int80\n");
+	set_eflags(get_eflags() | X86_EFLAGS_TF);
+	asm volatile ("int $0x80" : "=a" (tmp) : "a" (SYS_getpid)
+			: INT80_CLOBBERS);
+	check_result();
+#endif
+
+	/*
+	 * This test is particularly interesting if fast syscalls use
+	 * SYSENTER: it triggers a nasty design flaw in SYSENTER.
+	 * Specifically, SYSENTER does not clear TF, so either SYSENTER
+	 * or the next instruction traps at CPL0.  (Of course, Intel
+	 * mostly forgot to document exactly what happens here.)  So we
+	 * get a CPL0 fault with usergs (on 64-bit kernels) and possibly
+	 * no stack.  The only sane way the kernel can possibly handle
+	 * it is to clear TF on return from the #DB handler, but this
+	 * happens way too early to set TF in the saved pt_regs, so the
+	 * kernel has to do something clever to avoid losing track of
+	 * the TF bit.
+	 *
+	 * Needless to say, we've had bugs in this area.
+	 */
+	syscall(SYS_getpid);  /* Force symbol binding without TF set. */
+	printf("[RUN]\tSet TF and check a fast syscall\n");
+	set_eflags(get_eflags() | X86_EFLAGS_TF);
+	syscall(SYS_getpid);
+	check_result();
+
+	/* Now make sure that another fast syscall doesn't set TF again. */
+	fast_syscall_no_tf();
+
+	/*
+	 * And do a forced SYSENTER to make sure that this works even if
+	 * fast syscalls don't use SYSENTER.
+	 *
+	 * Invoking SYSENTER directly breaks all the rules.  Just handle
+	 * the SIGSEGV.
+	 */
+	if (sigsetjmp(jmpbuf, 1) == 0) {
+		unsigned long nr = SYS_getpid;
+		printf("[RUN]\tSet TF and check SYSENTER\n");
+		stack_t stack = {
+			.ss_sp = malloc(sizeof(char) * SIGSTKSZ),
+			.ss_size = SIGSTKSZ,
+		};
+		if (sigaltstack(&stack, NULL) != 0)
+			err(1, "sigaltstack");
+		sethandler(SIGSEGV, print_and_longjmp,
+			   SA_RESETHAND | SA_ONSTACK);
+		sethandler(SIGILL, print_and_longjmp, SA_RESETHAND);
+		set_eflags(get_eflags() | X86_EFLAGS_TF);
+		free(stack.ss_sp);
+		/* Clear EBP first to make sure we segfault cleanly. */
+		asm volatile ("xorl %%ebp, %%ebp; SYSENTER" : "+a" (nr) :: "flags", "rcx"
+#ifdef __x86_64__
+				, "r11"
+#endif
+			);
+
+		/* We're unreachable here.  SYSENTER forgets RIP. */
+	}
+	clearhandler(SIGSEGV);
+	clearhandler(SIGILL);
+	if (!(sig_eflags & X86_EFLAGS_TF)) {
+		printf("[FAIL]\tTF was cleared\n");
+		exit(1);
+	}
+
+	/* Now make sure that another fast syscall doesn't set TF again. */
+	fast_syscall_no_tf();
+
+	return 0;
+}