selftests/x86: Add check_initial_reg_state()

This checks that ELF binaries are started with an appropriately
blank register state.

( There's currently a nasty special case in the entry asm to
  arrange for this. I'm planning on removing the special case,
  and this will help make sure I don't break it. )

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/ef54f8d066b30a3eb36bbf26300eebb242185700.1454022279.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index 9c81f26..df4f767 100644 (file)
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -4,7 +4,8 @@ include ../lib.mk
 
 .PHONY: all all_32 all_64 warn_32bit_failure clean
 
-TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt ptrace_syscall
+TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt ptrace_syscall \
+                       check_initial_reg_state
 TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault sigreturn test_syscall_vdso unwind_vdso \
                        test_FCMOV test_FCOMI test_FISTTP \
                        ldt_gdt \
@@ -66,3 +67,9 @@ endif
 sysret_ss_attrs_64: thunks.S
 ptrace_syscall_32: raw_syscall_helper_32.S
 test_syscall_vdso_32: thunks_32.S
+
+# check_initial_reg_state is special: it needs a custom entry, and it
+# needs to be static so that its interpreter doesn't destroy its initial
+# state.
+check_initial_reg_state_32: CFLAGS += -Wl,-ereal_start -static
+check_initial_reg_state_64: CFLAGS += -Wl,-ereal_start -static

diff --git a/tools/testing/selftests/x86/check_initial_reg_state.c b/tools/testing/selftests/x86/check_initial_reg_state.c
new file mode 100644 (file)
index 0000000..6aaed9b
--- /dev/null
+++ b/tools/testing/selftests/x86/check_initial_reg_state.c
@@ -0,0 +1,109 @@
+/*
+ * check_initial_reg_state.c - check that execve sets the correct state
+ * Copyright (c) 2014-2016 Andrew Lutomirski
+ *
+ * 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.
+ */
+
+#define _GNU_SOURCE
+
+#include <stdio.h>
+
+unsigned long ax, bx, cx, dx, si, di, bp, sp, flags;
+unsigned long r8, r9, r10, r11, r12, r13, r14, r15;
+
+asm (
+       ".pushsection .text\n\t"
+       ".type real_start, @function\n\t"
+       ".global real_start\n\t"
+       "real_start:\n\t"
+#ifdef __x86_64__
+       "mov %rax, ax\n\t"
+       "mov %rbx, bx\n\t"
+       "mov %rcx, cx\n\t"
+       "mov %rdx, dx\n\t"
+       "mov %rsi, si\n\t"
+       "mov %rdi, di\n\t"
+       "mov %rbp, bp\n\t"
+       "mov %rsp, sp\n\t"
+       "mov %r8, r8\n\t"
+       "mov %r9, r9\n\t"
+       "mov %r10, r10\n\t"
+       "mov %r11, r11\n\t"
+       "mov %r12, r12\n\t"
+       "mov %r13, r13\n\t"
+       "mov %r14, r14\n\t"
+       "mov %r15, r15\n\t"
+       "pushfq\n\t"
+       "popq flags\n\t"
+#else
+       "mov %eax, ax\n\t"
+       "mov %ebx, bx\n\t"
+       "mov %ecx, cx\n\t"
+       "mov %edx, dx\n\t"
+       "mov %esi, si\n\t"
+       "mov %edi, di\n\t"
+       "mov %ebp, bp\n\t"
+       "mov %esp, sp\n\t"
+       "pushfl\n\t"
+       "popl flags\n\t"
+#endif
+       "jmp _start\n\t"
+       ".size real_start, . - real_start\n\t"
+       ".popsection");
+
+int main()
+{
+       int nerrs = 0;
+
+       if (sp == 0) {
+               printf("[FAIL]\tTest was built incorrectly\n");
+               return 1;
+       }
+
+       if (ax || bx || cx || dx || si || di || bp
+#ifdef __x86_64__
+           || r8 || r9 || r10 || r11 || r12 || r13 || r14 || r15
+#endif
+               ) {
+               printf("[FAIL]\tAll GPRs except SP should be 0\n");
+#define SHOW(x) printf("\t" #x " = 0x%lx\n", x);
+               SHOW(ax);
+               SHOW(bx);
+               SHOW(cx);
+               SHOW(dx);
+               SHOW(si);
+               SHOW(di);
+               SHOW(bp);
+               SHOW(sp);
+#ifdef __x86_64__
+               SHOW(r8);
+               SHOW(r9);
+               SHOW(r10);
+               SHOW(r11);
+               SHOW(r12);
+               SHOW(r13);
+               SHOW(r14);
+               SHOW(r15);
+#endif
+               nerrs++;
+       } else {
+               printf("[OK]\tAll GPRs except SP are 0\n");
+       }
+
+       if (flags != 0x202) {
+               printf("[FAIL]\tFLAGS is 0x%lx, but it should be 0x202\n", flags);
+               nerrs++;
+       } else {
+               printf("[OK]\tFLAGS is 0x202\n");
+       }
+
+       return nerrs ? 1 : 0;
+}