[PATCH v2] x86/asm/entry/32, selftests: Add test_syscall_vdso test

Denys Vlasenko
2015-06-12T15:29:53Z

The test is fairly simplistic: it checks that all registers
are preserved across 32-bit syscall via VDSO.

Run-tested:

$ ./test_syscall_vdso_32
[RUN] Executing 6-argument 32-bit syscall via VDSO
[Ok] Arguments are preserved across syscall
[RUN] Executing 6-argument 32-bit syscall via INT 80
[Ok] Arguments are preserved across syscall
[RUN] Running tests under ptrace
[RUN] Executing 6-argument 32-bit syscall via VDSO
[Ok] Arguments are preserved across syscall
[RUN] Executing 6-argument 32-bit syscall via INT 80
[Ok] Arguments are preserved across syscall

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ingo Molnar <mingo@kernel.org>
CC: Borislav Petkov <bp@alien8.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Alexei Starovoitov <ast@plumgrid.com>
CC: Will Drewry <wad@chromium.org>
CC: Kees Cook <keescook@chromium.org>
CC: x86@kernel.org
CC: linux-kernel@vger.kernel.org
---
Changes in v2:
does not fail if VDSO can't be found;
tests INT 80 syscall method;
tests syscalls under ptrace;
switched to /* */ comments

tools/testing/selftests/x86/Makefile | 2 +-
tools/testing/selftests/x86/test_syscall_vdso.c | 271 ++++++++++++++++++++++++
2 files changed, 272 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/x86/test_syscall_vdso.c

diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index caa60d5..84effa6 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -5,7 +5,7 @@ include ../lib.mk
.PHONY: all all_32 all_64 warn_32bit_failure clean

TARGETS_C_BOTHBITS := sigreturn single_step_syscall sysret_ss_attrs
-TARGETS_C_32BIT_ONLY := entry_from_vm86
+TARGETS_C_32BIT_ONLY := entry_from_vm86 test_syscall_vdso

TARGETS_C_32BIT_ALL := $(TARGETS_C_BOTHBITS) $(TARGETS_C_32BIT_ONLY)
BINARIES_32 := $(TARGETS_C_32BIT_ALL:%=%_32)
diff --git a/tools/testing/selftests/x86/test_syscall_vdso.c b/tools/testing/selftests/x86/test_syscall_vdso.c
new file mode 100644
index 0000000..7112e9d
--- /dev/null
+++ b/tools/testing/selftests/x86/test_syscall_vdso.c
@@ -0,0 +1,271 @@
+/*
+ * 32-bit syscall ABI conformance test.
+ *
+ * Copyright (c) 2015 Denys Vlasenko
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ */
+#undef _GNU_SOURCE
+#define _GNU_SOURCE 1
+#undef __USE_GNU
+#define __USE_GNU 1
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <signal.h>
+#include <sys/types.h>
+#include <sys/select.h>
+#include <sys/time.h>
+#include <elf.h>
+#include <sys/ptrace.h>
+#include <sys/wait.h>
+
+#if !defined(__i386__)
+int main(int argc, char **argv, char **envp)
+{
+ printf("[SKIP] Not a 32-bit x86\n");
+ return 0;
+}
+#else
+
+/*
+ * TODO: check r8..15 for info leaks.
+ */
+
+extern char int80;
+asm (
+ " .pushsection .text\n"
+ " .global int80\n"
+ "int80:\n"
+ " int $0x80\n"
+ " ret\n"
+ " .popsection"
+);
+
+long syscall_addr;
+long get_syscall(char **envp)
+{
+ Elf32_auxv_t *auxv;
+ while (*envp++ != NULL)
+ continue;
+ for (auxv = (void *)envp; auxv->a_type != AT_NULL; auxv++)
+ if (auxv->a_type == AT_SYSINFO)
+ return auxv->a_un.a_val;
+ printf("[WARN]\tAT_SYSINFO not supplied\n");
+ return 0;
+}
+
+int nfds;
+fd_set rfds;
+fd_set wfds;
+fd_set efds;
+struct timespec timeout;
+sigset_t sigmask;
+struct {
+ sigset_t *sp;
+ int sz;
+} sigmask_desc;
+
+void prep_args()
+{
+ nfds = 42;
+ FD_ZERO(&rfds);
+ FD_ZERO(&wfds);
+ FD_ZERO(&efds);
+ FD_SET(0, &rfds);
+ FD_SET(1, &wfds);
+ FD_SET(2, &efds);
+ timeout.tv_sec = 0;
+ timeout.tv_nsec = 123;
+ sigemptyset(&sigmask);
+ sigaddset(&sigmask, SIGINT);
+ sigaddset(&sigmask, SIGUSR2);
+ sigaddset(&sigmask, SIGRTMAX);
+ sigmask_desc.sp = &sigmask;
+ sigmask_desc.sz = 8; /* bytes */
+}
+
+static void print_flags(const char *name, unsigned long r)
+{
+ static const char *bitarray[] = {
+ "\n" ,"c\n" ,/* Carry Flag */
+ "0 " ,"1 " ,/* Bit 1 - always on */
+ "" ,"p " ,/* Parity Flag */
+ "0 " ,"3? " ,
+ "" ,"a " ,/* Auxiliary carry Flag */
+ "0 " ,"5? " ,
+ "" ,"z " ,/* Zero Flag */
+ "" ,"s " ,/* Sign Flag */
+ "" ,"t " ,/* Trap Flag */
+ "" ,"i " ,/* Interrupt Flag */
+ "" ,"d " ,/* Direction Flag */
+ "" ,"o " ,/* Overflow Flag */
+ "0 " ,"1 " ,/* I/O Privilege Level (2 bits) */
+ "0" ,"1" ,/* I/O Privilege Level (2 bits) */
+ "" ,"n " ,/* Nested Task */
+ "0 " ,"15? ",
+ "" ,"r " ,/* Resume Flag */
+ "" ,"v " ,/* Virtual Mode */
+ "" ,"ac " ,/* Alignment Check/Access Control */
+ "" ,"vif ",/* Virtual Interrupt Flag */
+ "" ,"vip ",/* Virtual Interrupt Pending */
+ "" ,"id " ,/* CPUID detection */
+ NULL
+ };
+ const char **bitstr;
+ int bit;
+
+ printf("%s=%016lx ", name, r);
+ bitstr = bitarray + 42;
+ bit = 21;
+ if ((r >> 22) != 0)
+ printf("(extra bits are set) ");
+ do {
+ if (bitstr[(r >> bit) & 1][0])
+ printf(bitstr[(r >> bit) & 1]);
+ bitstr -= 2;
+ bit--;
+ } while (bit >= 0);
+}
+
+int run_syscall(void)
+{
+ long flags, bad_arg;
+
+ prep_args();
+
+ asm("\n"
+ /* Try 6-arg syscall: pselect. It should return quickly */
+ " push %%ebp\n"
+ " mov $308, %%eax\n" /* PSELECT */
+ " mov nfds, %%ebx\n" /* ebx arg1 */
+ " mov $rfds, %%ecx\n" /* ecx arg2 */
+ " mov $wfds, %%edx\n" /* edx arg3 */
+ " mov $efds, %%esi\n" /* esi arg4 */
+ " mov $timeout, %%edi\n" /* edi arg5 */
+ " mov $sigmask_desc, %%ebp\n" /* %ebp arg6 */
+ " push $0x200ed7\n" /* set almost all flags */
+ " popf\n" /* except TF, IOPL, NT, RF, VM, AC, VIF, VIP */
+ " call *syscall_addr\n"
+ /* Check that registers are not clobbered */
+ " pushf\n"
+ " pop %%eax\n"
+ " cld\n"
+ " cmp nfds, %%ebx\n" /* ebx arg1 */
+ " mov $1, %%ebx\n"
+ " jne 1f\n"
+ " cmp $rfds, %%ecx\n" /* ecx arg2 */
+ " mov $2, %%ebx\n"
+ " jne 1f\n"
+ " cmp $wfds, %%edx\n" /* edx arg3 */
+ " mov $3, %%ebx\n"
+ " jne 1f\n"
+ " cmp $efds, %%esi\n" /* esi arg4 */
+ " mov $4, %%ebx\n"
+ " jne 1f\n"
+ " cmp $timeout, %%edi\n" /* edi arg5 */
+ " mov $5, %%ebx\n"
+ " jne 1f\n"
+ " cmpl $sigmask_desc, %%ebp\n" /* %ebp arg6 */
+ " mov $6, %%ebx\n"
+ " jne 1f\n"
+ " mov $0, %%ebx\n"
+ "1:\n"
+ " pop %%ebp\n"
+ : "=a" (flags), "=b" (bad_arg)
+ :
+ : "cx", "dx", "si", "di"
+ );
+
+ /*
+ * On paravirt kernels, flags are not preserved across syscalls.
+ * Thus, we do not consider it a bug if some are changed.
+ * We just show ones which do.
+ */
+ if ((0x200ed7 ^ flags) != 0) {
+ print_flags("[WARN]\tFlags before", 0x200ed7);
+ print_flags("[WARN]\tFlags after", flags);
+ print_flags("[WARN]\tChanged", (0x200ed7 ^ flags));
+ }
+
+ if (bad_arg) {
+ printf("[FAIL]\targ#%ld clobbered\n", bad_arg);
+ return 1;
+ }
+ printf("[Ok]\tArguments are preserved across syscall\n");
+ return 0;
+}
+
+int run_syscall_twice()
+{
+ int exitcode = 0;
+ long sv;
+
+ if (syscall_addr) {
+ printf("[RUN]\tExecuting 6-argument 32-bit syscall via VDSO\n");
+ exitcode = run_syscall();
+ }
+ sv = syscall_addr;
+ syscall_addr = (long)&int80;
+ printf("[RUN]\tExecuting 6-argument 32-bit syscall via INT 80\n");
+ exitcode += run_syscall();
+ syscall_addr = sv;
+ return exitcode;
+}
+
+void ptrace_me()
+{
+ pid_t pid;
+
+ fflush(NULL);
+ pid = fork();
+ if (pid < 0)
+ exit(1);
+ if (pid == 0) {
+ /* child */
+ if (ptrace(PTRACE_TRACEME, 0L, 0L, 0L) != 0)
+ exit(0);
+ raise(SIGSTOP);
+ return;
+ }
+ /* parent */
+ printf("[RUN]\tRunning tests under ptrace\n");
+ while (1) {
+ int status;
+ pid = waitpid(-1, &status, __WALL);
+ if (pid < 0 || !WIFSTOPPED(status))
+ break;
+ /*
+ * Note: we do not inject sig = WSTOPSIG(status).
+ * We probably should, but careful: do not inject SIGTRAP
+ * generated by syscall entry/exit stops.
+ * That kills the child.
+ */
+ ptrace(PTRACE_SYSCALL, pid, 0L, 0L /*sig*/);
+ }
+ exit(0);
+}
+
+int main(int argc, char **argv, char **envp)
+{
+ int exitcode = 0;
+
+ /* This only works for non-static builds:
+ * syscall_addr = dlsym(dlopen("linux-gate.so.1", RTLD_NOW), "__kernel_vsyscall");
+ */
+ syscall_addr = get_syscall(envp);
+
+ exitcode += run_syscall_twice();
+ ptrace_me();
+ exitcode += run_syscall_twice();
+
+ return 0;
+}
+#endif
--
1.8.1.4