x86/asm/entry/32, selftests: Add 'test_syscall_vdso' test

This new test checks that all x86 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 the syscall is called and are 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@redhat.com>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1442427809-2027-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 55 insertions, 0 deletions

diff --git a/tools/testing/selftests/x86/thunks_32.S b/tools/testing/selftests/x86/thunks_32.S
new file mode 100644
index 000000000000..29b644bb9f2f
--- /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 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