[PATCH v3 RESEND] x86/asm/entry/32, selftests: Add test_syscall_vdso test

[Denys Vlasenko]

The test checks that all registers are preserved across
32-bit syscalls. It tests syscalls through VDSO
(if available) and through INT 0x80, normally
and under ptrace.

If kernel is a 64-bit one, high registers (r8..r15) are poisoned
before call and checked afterwards. They must be either preserved,
or cleared to zero (but r11 is special); r12..15 must be preserved
for INT 0x80.

EFLAGS is checked for changes too, but change there is not considered
to be a bug (paravirt kernels do not preserve arithmetic flags).

Run-tested on 64-bit kernel:

$ ./test_syscall_vdso_32
[RUN]	Executing 6-argument 32-bit syscall via VDSO
[OK]	Arguments are preserved across syscall
[NOTE]	R11 has changed:0000000000200ed7 - assuming clobbered by SYSRET insn
[OK]	R8..R15 did not leak kernel data
[RUN]	Executing 6-argument 32-bit syscall via INT 80
[OK]	Arguments are preserved across syscall
[OK]	R8..R15 did not leak kernel data
[RUN]	Running tests under ptrace
[RUN]	Executing 6-argument 32-bit syscall via VDSO
[OK]	Arguments are preserved across syscall
[OK]	R8..R15 did not leak kernel data
[RUN]	Executing 6-argument 32-bit syscall via INT 80
[OK]	Arguments are preserved across syscall
[OK]	R8..R15 did not leak kernel data

On 32-bit paravirt kernel:

$ ./test_syscall_vdso_32
[NOTE]	Not a 64-bit kernel, won't test R8..R15 leaks
[RUN]	Executing 6-argument 32-bit syscall via VDSO
[WARN]	Flags before=0000000000200ed7 id 0 00 o d i s z 0 a 0 p 1 c
[WARN]	Flags  after=0000000000200246 id 0 00 i z 0 0 p 1
[WARN]	Flags change=0000000000000c91 0 00 o d s 0 a 0 0 c
[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@xxxxxxxxxx>
CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: Borislav Petkov <bp@xxxxxxxxx>
CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
CC: Oleg Nesterov <oleg@xxxxxxxxxx>
CC: Frederic Weisbecker <fweisbec@xxxxxxxxx>
CC: Alexei Starovoitov <ast@xxxxxxxxxxxx>
CC: Will Drewry <wad@xxxxxxxxxxxx>
CC: Kees Cook <keescook@xxxxxxxxxxxx>
CC: x86@xxxxxxxxxx
CC: linux-kernel@xxxxxxxxxxxxxxx
---

Changes in v2:
 does not fail if VDSO can't be found;
 tests INT 80 syscall method;
 tests syscalls under ptrace;
 switched to /* */ comments

Changes in v3:
 added checking for r8..r15 info leaks

 tools/testing/selftests/x86/test_syscall_vdso.c | 401 ++++++++++++++++++++++++
 tools/testing/selftests/x86/thunks_32.S         |  55 ++++
 2 files changed, 456 insertions(+)
 create mode 100644 tools/testing/selftests/x86/test_syscall_vdso.c
 create mode 100644 tools/testing/selftests/x86/thunks_32.S

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..0792aef
--- /dev/null
+++ b/tools/testing/selftests/x86/test_syscall_vdso.c
@@ -0,0 +1,401 @@
+/*
+ * 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.
+ */
+/*
+ * Can be built statically:
+ * gcc -Os -Wall -static -m32 test_syscall_vdso.c thunks_32.S
+ */
+#undef _GNU_SOURCE
+#define _GNU_SOURCE 1
+#undef __USE_GNU
+#define __USE_GNU 1
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.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]\tNot a 32-bit x86 userspace\n");
+	return 0;
+}
+#else
+
+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;
+}
+
+asm (
+	"	.pushsection .text\n"
+	"	.global	int80\n"
+	"int80:\n"
+	"	int	$0x80\n"
+	"	ret\n"
+	"	.popsection\n"
+);
+extern char int80;
+
+struct regs64 {
+	uint64_t rax, rbx, rcx, rdx;
+	uint64_t rsi, rdi, rbp, rsp;
+	uint64_t r8,  r9,  r10, r11;
+	uint64_t r12, r13, r14, r15;
+};
+struct regs64 regs64;
+int kernel_is_64bit;
+
+asm (
+	"	.pushsection .text\n"
+	"	.code64\n"
+	"get_regs64:\n"
+	"	push	%rax\n"
+	"	mov	$regs64, %eax\n"
+	"	pop	0*8(%rax)\n"
+	"	movq	%rbx, 1*8(%rax)\n"
+	"	movq	%rcx, 2*8(%rax)\n"
+	"	movq	%rdx, 3*8(%rax)\n"
+	"	movq	%rsi, 4*8(%rax)\n"
+	"	movq	%rdi, 5*8(%rax)\n"
+	"	movq	%rbp, 6*8(%rax)\n"
+	"	movq	%rsp, 7*8(%rax)\n"
+	"	movq	%r8,  8*8(%rax)\n"
+	"	movq	%r9,  9*8(%rax)\n"
+	"	movq	%r10, 10*8(%rax)\n"
+	"	movq	%r11, 11*8(%rax)\n"
+	"	movq	%r12, 12*8(%rax)\n"
+	"	movq	%r13, 13*8(%rax)\n"
+	"	movq	%r14, 14*8(%rax)\n"
+	"	movq	%r15, 15*8(%rax)\n"
+	"	ret\n"
+	"poison_regs64:\n"
+	"	movq	$0x7f7f7f7f, %r8\n"
+	"	shl	$32, %r8\n"
+	"	orq	$0x7f7f7f7f, %r8\n"
+	"	movq	%r8, %r9\n"
+	"	movq	%r8, %r10\n"
+	"	movq	%r8, %r11\n"
+	"	movq	%r8, %r12\n"
+	"	movq	%r8, %r13\n"
+	"	movq	%r8, %r14\n"
+	"	movq	%r8, %r15\n"
+	"	ret\n"
+	"	.code32\n"
+	"	.popsection\n"
+);
+extern void get_regs64(void);
+extern void poison_regs64(void);
+extern unsigned long call64_from_32(void (*function)(void));
+void print_regs64(void)
+{
+	if (!kernel_is_64bit)
+		return;
+	printf("ax:%016llx bx:%016llx cx:%016llx dx:%016llx\n", regs64.rax,  regs64.rbx,  regs64.rcx,  regs64.rdx);
+	printf("si:%016llx di:%016llx bp:%016llx sp:%016llx\n", regs64.rsi,  regs64.rdi,  regs64.rbp,  regs64.rsp);
+	printf(" 8:%016llx  9:%016llx 10:%016llx 11:%016llx\n", regs64.r8 ,  regs64.r9 ,  regs64.r10,  regs64.r11);
+	printf("12:%016llx 13:%016llx 14:%016llx 15:%016llx\n", regs64.r12,  regs64.r13,  regs64.r14,  regs64.r15);
+}
+
+int check_regs64(void)
+{
+	int err = 0;
+	int num = 8;
+	uint64_t *r64 = &regs64.r8;
+
+	if (!kernel_is_64bit)
+		return 0;
+
+	do {
+		if (*r64 == 0x7f7f7f7f7f7f7f7fULL)
+			continue; /* register did not change */
+		if (syscall_addr != (long)&int80) {
+			/*
+			 * Non-INT80 syscall entrypoints are allowed to clobber R8+ regs:
+			 * either clear them to 0, or for R11, load EFLAGS.
+			 */
+			if (*r64 == 0)
+				continue;
+			if (num == 11) {
+				printf("[NOTE]\tR11 has changed:%016llx - assuming clobbered by SYSRET insn\n", *r64);
+				continue;
+			}
+		} else {
+			/* INT80 syscall entrypoint can be used by
+			 * 64-bit programs too, unlike SYSCALL/SYSENTER.
+			 * Therefore it must preserve R12+
+			 * (they are callee-saved registers in 64-bit C ABI).
+			 *
+			 * This was probably historically not intended,
+			 * but R8..11 are clobbered (cleared to 0).
+			 * IOW: they are the only registers which aren't
+			 * preserved across INT80 syscall.
+			 */
+			if (*r64 == 0 && num <= 11)
+				continue;
+		}
+		printf("[FAIL]\tR%d has changed:%016llx\n", num, *r64);
+		err++;
+	} while (r64++, ++num < 16);
+
+	if (!err)
+		printf("[OK]\tR8..R15 did not leak kernel data\n");
+	return err;
+}
+
+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();
+
+	if (kernel_is_64bit)
+		call64_from_32(poison_regs64);
+	/*print_regs64();*/
+
+	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"
+	);
+
+	if (kernel_is_64bit) {
+		memset(&regs64, 0x77, sizeof(regs64));
+		call64_from_32(get_regs64);
+		/*print_regs64();*/
+	}
+
+	/*
+	 * 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]\tFlags change", (0x200ed7 ^ flags));
+	}
+
+	if (bad_arg) {
+		printf("[FAIL]\targ#%ld clobbered\n", bad_arg);
+		return 1;
+	}
+	printf("[OK]\tArguments are preserved across syscall\n");
+
+	return check_regs64();
+}
+
+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 (WIFEXITED(status))
+			exit(WEXITSTATUS(status));
+		if (WIFSIGNALED(status))
+			exit(WTERMSIG(status));
+		if (pid <= 0 || !WIFSTOPPED(status)) /* paranoia */
+			exit(255);
+		/*
+		 * 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*/);
+	}
+}
+
+int main(int argc, char **argv, char **envp)
+{
+	int exitcode = 0;
+	int cs;
+
+	asm("\n"
+	"	movl	%%cs, %%eax\n"
+	: "=a" (cs)
+	);
+	kernel_is_64bit = (cs == 0x23);
+	if (!kernel_is_64bit)
+		printf("[NOTE]\tNot a 64-bit kernel, won't test R8..R15 leaks\n");
+
+	/* 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 exitcode;
+}
+#endif
diff --git a/tools/testing/selftests/x86/thunks_32.S b/tools/testing/selftests/x86/thunks_32.S
new file mode 100644
index 0000000..77e9159
--- /dev/null
+++ b/tools/testing/selftests/x86/thunks_32.S
@@ -0,0 +1,55 @@
+/*
+ * thunks_32.S - assembly helpers for mixed-bitness code
+ * Copyright (c) 2015 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.
+ *
+ * These are little helpers that make it easier to switch bitness on
+ * the fly.
+ */
+
+	.text
+	.code32
+
+	.global call64_from_32
+	.type call32_from_64, @function
+
+	// 4(%esp): function to call
+call64_from_32:
+	// Fetch function address
+	mov	4(%esp), %eax
+
+	// Save registers which are callee-clobbered by 64-bit ABI
+	push	%ecx
+	push	%edx
+	push	%esi
+	push	%edi
+
+	// Switch to long mode
+	jmp	$0x33,$1f
+1:	.code64
+
+	// Call the function
+	call	*%rax
+
+	// Switch to compatibility mode
+	push	$0x23  /* USER32_CS */
+	.code32; push $1f; .code64 /* hack: can't have X86_64_32S relocation in 32-bit ELF */
+	lretq
+1:	.code32
+
+	pop	%edi
+	pop	%esi
+	pop	%edx
+	pop	%ecx
+
+	ret
+
+.size call64_from_32, .-call64_from_32
-- 
1.8.1.4

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