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Message-ID: <CAGXu5jK6d0AoW5PpUrA_LY_WjNRoXBoe4bciSdsyO78BG_rduQ@mail.gmail.com>
Date: Wed, 10 Jun 2015 13:00:16 -0700
From: Kees Cook <keescook@...omium.org>
To: Denys Vlasenko <dvlasenk@...hat.com>
Cc: "CC: Ingo Molnar" <mingo@...nel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Steven Rostedt <rostedt@...dmis.org>,
Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...capital.net>,
Oleg Nesterov <oleg@...hat.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Alexei Starovoitov <ast@...mgrid.com>,
Will Drewry <wad@...omium.org>,
"x86@...nel.org" <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/asm/entry/32, selftests: Add test_syscall_vdso test
On Wed, Jun 10, 2015 at 9:59 AM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
> The test is fairly simplistic: it checks that all registers
> are preserved across 32-bit syscall via VDSO.
>
> Run-tested.
>
> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
> CC: Linus Torvalds <torvalds@...ux-foundation.org>
> CC: Steven Rostedt <rostedt@...dmis.org>
> CC: Ingo Molnar <mingo@...nel.org>
> CC: Borislav Petkov <bp@...en8.de>
> CC: "H. Peter Anvin" <hpa@...or.com>
> CC: Andy Lutomirski <luto@...capital.net>
> CC: Oleg Nesterov <oleg@...hat.com>
> CC: Frederic Weisbecker <fweisbec@...il.com>
> CC: Alexei Starovoitov <ast@...mgrid.com>
> CC: Will Drewry <wad@...omium.org>
> CC: Kees Cook <keescook@...omium.org>
> CC: x86@...nel.org
> CC: linux-kernel@...r.kernel.org
> ---
> tools/testing/selftests/x86/Makefile | 2 +-
> tools/testing/selftests/x86/test_syscall_vdso.c | 198 ++++++++++++++++++++++++
> 2 files changed, 199 insertions(+), 1 deletion(-)
> create mode 100644 tools/testing/selftests/x86/test_syscall_vdso.c
I love tests! Very nice. :)
Reviewed-by: Kees Cook <keescook@...omium.org>
> 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..78e6efb
> --- /dev/null
> +++ b/tools/testing/selftests/x86/test_syscall_vdso.c
> @@ -0,0 +1,198 @@
> +/*
> + * 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/select.h>
> +#include <sys/time.h>
> +#include <sys/types.h>
> +#include <elf.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.
> +//TODO: run this test twice, second time under ptrace.
Minor nit-pick: I would recommend using /* */-style comments, not
//-style. And checkpatch.pl would yell too. :)
> +
> +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("[SKIP]\tAT_SYSINFO not supplied, can't test\n");
> + exit(0); /* this is not a test failure */
Why is that not a test failure? It would mean it didn't actually test
anything, which seems like a failure to me.
> +}
> +
> +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 main(int argc, char **argv, char **envp)
> +{
> + long flags, bad_arg;
> +
> + // This only works for non-static builds:
> + //syscall_addr = dlsym(dlopen("linux-gate.so.1", RTLD_NOW), "__kernel_vsyscall");
> + syscall_addr = get_syscall(envp);
> +
> + prep_args();
> +
> + printf("[RUN] executing 6-argument 32-bit syscall\n");
> +
> + 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] flags before", 0x200ed7);
> + print_flags("[WARN] flags after", flags);
> + print_flags("[WARN] changed", (0x200ed7 ^ flags));
> + }
> +
> + if (bad_arg) {
> + printf("[FAIL] arg#%ld clobbered\n", bad_arg);
> + return 1;
> + }
> + printf("[Ok] arguments are preserved across syscalls\n");
> + return 0;
> +}
> +#endif
> --
> 1.8.1.4
>
Thanks!
-Kees
--
Kees Cook
Chrome OS Security
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