Re: [Qemu-devel] [qemu-s390x] linux-user: s390x issue on Fedora 30 (dynamic library loader?)

[Aleksandar Markovic]

On Mon, Aug 19, 2019 at 3:34 PM Aleksandar Markovic <
address@hidden> wrote:

> Hi, David.
>
> I can't repro the problem either, but I do have a patch authored by an
> engineer that left the company a while ago that seems to be at least
> related to your scenario. May I ask you to test it (just apply it to QEMU
> ToT and rerun the scenario to see if it changes the outcome) (feel free to
> experiment and modify the changes)? I never managed to understand the
> purpose of that patch (I lost the contact with the former engineer, and the
> patch is without any comment), so I never dared to send it to the list, but
> I hope your scenario may actually explain the purpose and the origin of the
> patch.
>
> I am attaching the patch both as a file and inline.
>
>
In the patch I had sent in my previous mail, TARGET_ENONET should be
replaced by TARGET_ENOENT. I made a mistake while doing speedy rebasing.
Though, both ENONET and ENOENT compile, and perhaps the error code value is
not crucial. I am attaching the updated/corrected patch.

Aleksandar


> Yours,
> Aleksandar
>
>
> From 377f99e807f4aa42ece9f0cd437f50af11611b4c Mon Sep 17 00:00:00 2001
> From: Aleksandar Markovic <address@hidden>
> Date: Mon, 19 Aug 2019 15:20:29 +0200
> Subject: [PATCH] linux-user: Special case /etc/ld.cache.so and pretend it
> does
>  not exist
>
> Prevent target executables from opening host ld.so.cache.
> ---
>  linux-user/syscall.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 8367cb1..f5bae6e 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -8820,6 +8820,10 @@ static abi_long do_syscall1(void *cpu_env, int num,
> abi_long arg1,
>          if (!(p = lock_user_string(arg1))) {
>              return -TARGET_EFAULT;
>          }
> +        if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
> +            unlock_user(p, arg1, 0);
> +            return -TARGET_ENONET;
> +        }
>          ret = get_errno(statfs(path(p), &stfs));
>          unlock_user(p, arg1, 0);
>      convert_statfs:
> @@ -8859,6 +8863,10 @@ static abi_long do_syscall1(void *cpu_env, int num,
> abi_long arg1,
>          if (!(p = lock_user_string(arg1))) {
>              return -TARGET_EFAULT;
>          }
> +        if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
> +            unlock_user(p, arg1, 0);
> +            return -TARGET_ENONET;
> +        }
>          ret = get_errno(statfs(path(p), &stfs));
>          unlock_user(p, arg1, 0);
>      convert_statfs64:
> @@ -9059,6 +9067,10 @@ static abi_long do_syscall1(void *cpu_env, int num,
> abi_long arg1,
>          if (!(p = lock_user_string(arg1))) {
>              return -TARGET_EFAULT;
>          }
> +        if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
> +            unlock_user(p, arg1, 0);
> +            return -TARGET_ENONET;
> +        }
>          ret = get_errno(stat(path(p), &st));
>          unlock_user(p, arg1, 0);
>          goto do_stat;
> @@ -9068,6 +9080,10 @@ static abi_long do_syscall1(void *cpu_env, int num,
> abi_long arg1,
>          if (!(p = lock_user_string(arg1))) {
>              return -TARGET_EFAULT;
>          }
> +        if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
> +            unlock_user(p, arg1, 0);
> +            return -TARGET_ENONET;
> +        }
>          ret = get_errno(lstat(path(p), &st));
>          unlock_user(p, arg1, 0);
>          goto do_stat;
> @@ -10268,6 +10284,10 @@ static abi_long do_syscall1(void *cpu_env, int
> num, abi_long arg1,
>          if (!(p = lock_user_string(arg1))) {
>              return -TARGET_EFAULT;
>          }
> +        if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
> +            unlock_user(p, arg1, 0);
> +            return -TARGET_ENONET;
> +        }
>          ret = get_errno(stat(path(p), &st));
>          unlock_user(p, arg1, 0);
>          if (!is_error(ret))
> @@ -10279,6 +10299,10 @@ static abi_long do_syscall1(void *cpu_env, int
> num, abi_long arg1,
>          if (!(p = lock_user_string(arg1))) {
>              return -TARGET_EFAULT;
>          }
> +        if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
> +            unlock_user(p, arg1, 0);
> +            return -TARGET_ENONET;
> +        }
>          ret = get_errno(lstat(path(p), &st));
>          unlock_user(p, arg1, 0);
>          if (!is_error(ret))
> @@ -10319,6 +10343,10 @@ static abi_long do_syscall1(void *cpu_env, int
> num, abi_long arg1,
>              if (p == NULL) {
>                  return -TARGET_EFAULT;
>              }
> +            if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
> +                unlock_user(p, arg1, 0);
> +                return -TARGET_ENONET;
> +            }
>  #if defined(__NR_statx)
>              {
>                  /*
> --
> 2.7.4
>
>
> On Mon, Aug 19, 2019 at 3:08 PM David Hildenbrand <address@hidden>
> wrote:
>
>> On 19.08.19 14:11, Peter Maydell wrote:
>> > On Sat, 17 Aug 2019 at 17:14, David Hildenbrand <address@hidden>
>> wrote:
>> >>
>> >> On 17.08.19 17:59, David Hildenbrand wrote:
>> >>> Hi everybody,
>> >>>
>> >>> I was just trying to run qemu-s390x (linux-user) with a very simple
>> >>> binary (gzip + lib/ld64.so.1, compiled under Fedora 27). This used to
>> >>> work just fine a while ago (especially when I was working on vector
>> >>> instructions using QEMU v3.1). However, now I can't get past a
>> SEGFAULT
>> >>> in the dynamic library loader (I assume it is trying to locate
>> glibc). I
>> >>> tried a couple of other binaries that definitely used to work (from
>> >>> Fedora 30).
>> >>>
>> >>> I checked QEMU v4.1, v4.0 and v3.1. All are broken for me. Which is
>> >>> weird - because it used to work :/
>> >>>
>> >>> I remember that I was running Fedora 29 the last time I had it
>> running,
>> >>> so my gut feeling is that this is related to some other system library
>> >>> (but which?). I am running on an up-to-date Fedora 30 x86-64 now.
>> >>>
>> >>> Any ideas? Has this been reported already? (not sure if this is a
>> Fedora
>> >>> 30 issue)
>> >
>> > I'm pretty sure the problem you've run into is a long standing
>> > bug in the glibc dynamic loader. It cannot cope with the ld.so.cache
>> > being for the wrong endianness. (Correct endianness but incorrect
>> > architecture it correctly detects and ignores). The result is that
>> > running a linux-user QEMU dynamic binary for big-endian on little-endian
>> > like this will crash in the dynamic loader unless you arrange that it
>> can't
>> > find the host's ld.so.cache somehow, eg:
>> >  (a) run inside a chroot
>> >  (b) create an empty /etc/ld.so.cache file inside the -L directory
>> >
>> > The ideal fix would be if somebody cared enough to track down
>> > and fix the ld.so bug.
>> >
>> > Compare:
>> > https://bugs.launchpad.net/qemu/+bug/1701798
>> > https://bugs.launchpad.net/qemu/+bug/1835693
>> >
>> > thanks
>> > -- PMM
>> >
>>
>> Thanks, running
>>
>> "ldconfig -c etc/ld.so.cache -r ."
>>
>> Seems to fix the issue for me. So you are sure the bug resides in glic
>> and not in the qemu-user pieces of the library loader?
>>
>> --
>>
>> Thanks,
>>
>> David / dhildenb
>>
>>

0001-linux-user-Special-case-etc-ld.cache.so-and-pretend-.patch
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