linux-kernel - Re: [PATCHv5 3/3] selftest/x86: add mremap vdso 32-bit test

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Date:	Thu, 21 Apr 2016 13:01:20 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Dmitry Safonov <dsafonov@...tuozzo.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Dmitry Safonov <0x7f454c46@...il.com>,
	Shuah Khan <shuahkh@....samsung.com>,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCHv5 3/3] selftest/x86: add mremap vdso 32-bit test

On Mon, Apr 18, 2016 at 6:43 AM, Dmitry Safonov <dsafonov@...tuozzo.com> wrote:
> Should print on success:
> [root@...alhost ~]# ./test_mremap_vdso_32
>         AT_SYSINFO_EHDR is 0xf773f000
> [NOTE]  Moving vDSO: [f773f000, f7740000] -> [a000000, a001000]
> [OK]
> Or segfault if landing was bad (before patches):
> [root@...alhost ~]# ./test_mremap_vdso_32
>         AT_SYSINFO_EHDR is 0xf774f000
> [NOTE]  Moving vDSO: [f774f000, f7750000] -> [a000000, a001000]
> Segmentation fault (core dumped)
>
> Cc: Shuah Khan <shuahkh@....samsung.com>
> Cc: linux-kselftest@...r.kernel.org
> Suggested-by: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Dmitry Safonov <dsafonov@...tuozzo.com>
> ---
> v5: initial version
>
>  tools/testing/selftests/x86/Makefile           |  2 +-
>  tools/testing/selftests/x86/test_mremap_vdso.c | 72 ++++++++++++++++++++++++++
>  2 files changed, 73 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/x86/test_mremap_vdso.c
>
> diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
> index b47ebd170690..c7162b511ab0 100644
> --- a/tools/testing/selftests/x86/Makefile
> +++ b/tools/testing/selftests/x86/Makefile
> @@ -7,7 +7,7 @@ include ../lib.mk
>  TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt ptrace_syscall \
>                         check_initial_reg_state sigreturn ldt_gdt iopl
>  TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault test_syscall_vdso unwind_vdso \
> -                       test_FCMOV test_FCOMI test_FISTTP \
> +                       test_FCMOV test_FCOMI test_FISTTP test_mremap_vdso \
>                         vdso_restorer
>
>  TARGETS_C_32BIT_ALL := $(TARGETS_C_BOTHBITS) $(TARGETS_C_32BIT_ONLY)
> diff --git a/tools/testing/selftests/x86/test_mremap_vdso.c b/tools/testing/selftests/x86/test_mremap_vdso.c
> new file mode 100644
> index 000000000000..a470790e2118
> --- /dev/null
> +++ b/tools/testing/selftests/x86/test_mremap_vdso.c
> @@ -0,0 +1,72 @@
> +/*
> + * 32-bit test to check vdso mremap.
> + *
> + * Copyright (c) 2016 Dmitry Safonov
> + * Suggested-by: 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.
> + */
> +/*
> + * Can be built statically:
> + * gcc -Os -Wall -static -m32 test_mremap_vdso.c
> + */
> +#define _GNU_SOURCE
> +#include <stdio.h>
> +#include <errno.h>
> +#include <unistd.h>
> +#include <string.h>
> +
> +#include <sys/mman.h>
> +#include <sys/auxv.h>
> +#include <sys/syscall.h>
> +
> +#if !defined(__i386__)
> +int main(int argc, char **argv, char **envp)
> +{
> +       printf("[SKIP]\tNot a 32-bit x86 userspace\n");
> +       return 0;

What's wrong with testing on 64-bit systems?

> +}
> +#else
> +
> +#define PAGE_SIZE      4096
> +#define VDSO_SIZE      PAGE_SIZE

The vdso is frequently bigger than a page.

> +
> +int main(int argc, char **argv, char **envp)
> +{
> +       unsigned long vdso_addr, dest_addr;
> +       void *new_addr;
> +       const char *ok_string = "[OK]\n";
> +
> +       vdso_addr = getauxval(AT_SYSINFO_EHDR);
> +       printf("\tAT_SYSINFO_EHDR is 0x%lx\n", vdso_addr);
> +       if (!vdso_addr || vdso_addr == -ENOENT) {
> +               printf("[FAIL]\tgetauxval failed\n");
> +               return 1;

Let's make this [WARN] and return 0.  The vdso is optional, and
getauxval is missing on many systems.


> +       }
> +
> +       /* to low for stack, to high for lib/data/code mappings */
> +       dest_addr = 0x0a000000;

This could be make reliable -- map a big enough area PROT_NONE and use
that address.

> +       printf("[NOTE]\tMoving vDSO: [%lx, %lx] -> [%lx, %lx]\n",
> +               vdso_addr, vdso_addr + VDSO_SIZE,
> +               dest_addr, dest_addr + VDSO_SIZE);

fflush(stdout), please, for the benefit of test harnesses that use pipes.

--Andy

> +       new_addr = mremap((void *)vdso_addr, VDSO_SIZE, VDSO_SIZE,
> +                       MREMAP_FIXED|MREMAP_MAYMOVE, dest_addr);
> +       if ((unsigned long)new_addr == (unsigned long)-1) {
> +               printf("[FAIL]\tmremap failed (%d): %m\n", errno);
> +               return 1;
> +       }
> +
> +       asm volatile ("int $0x80" : : "a" (__NR_write), "b" (STDOUT_FILENO),
> +                       "c" (ok_string), "d" (strlen(ok_string)));
> +       asm volatile ("int $0x80" : : "a" (__NR_exit), "b" (0));
> +
> +       return 0;
> +}
> +#endif
> --
> 2.8.0
>



-- 
Andy Lutomirski
AMA Capital Management, LLC