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

[Dmitry Safonov]

On 04/21/2016 11:01 PM, Andy Lutomirski wrote:
> On Mon, Apr 18, 2016 at 6:43 AM, Dmitry Safonov <dsafonov@xxxxxxxxxxxxx> wrote:
> > Should print on success:
> > [root@localhost ~]# ./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@localhost ~]# ./test_mremap_vdso_32
> >          AT_SYSINFO_EHDR is 0xf774f000
> > [NOTE]  Moving vDSO: [f774f000, f7750000] -> [a000000, a001000]
> > Segmentation fault (core dumped)
> >
> > Cc: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
> > Cc: linux-kselftest@xxxxxxxxxxxxxxx
> > Suggested-by: Andy Lutomirski <luto@xxxxxxxxxx>
> > Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
> > ---
> > 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?

Ok, will drop this.

> > +}
> > +#else
> > +
> > +#define PAGE_SIZE      4096
> > +#define VDSO_SIZE      PAGE_SIZE
> The vdso is frequently bigger than a page.

Ok, will enlarge this. Are two pages big enough?

> > +
> > +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.

Ok

> > +       }
> > +
> > +       /* 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.

Oh, that's good, will do.

> > +       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.

Will add.

> > +       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


--
Regards,
Dmitry Safonov