From: Florian Weimer <fweimer@redhat.com>
To: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Cc: Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>,
jma14 <jma14@rice.edu>, Carlos O'Donell <carlos@redhat.com>,
John Mellor-Crummey <johnmc@rice.edu>
Subject: Re: [PATCH v10 2/4] elf: Fix initial-exec TLS access on audit modules (BZ #28096)
Date: Tue, 18 Jan 2022 14:02:11 +0100 [thread overview]
Message-ID: <875yqhjiy4.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <a607316e-cf5e-7d77-ebd1-2ee0e9d18685@linaro.org> (Adhemerval Zanella's message of "Tue, 18 Jan 2022 09:58:43 -0300")
* Adhemerval Zanella:
> On 18/01/2022 08:33, Florian Weimer wrote:
>> * Adhemerval Zanella via Libc-alpha:
>>
>>> diff --git a/elf/dl-tls.c b/elf/dl-tls.c
>>> index 8ba70c9a9d..8ed91ff599 100644
>>> --- a/elf/dl-tls.c
>>> +++ b/elf/dl-tls.c
>>> @@ -520,7 +520,7 @@ _dl_resize_dtv (dtv_t *dtv, size_t max_modid)
>>>
>>>
>>> void *
>>> -_dl_allocate_tls_init (void *result)
>>> +_dl_allocate_tls_init (void *result, bool init_tls)
>>> {
>>> if (result == NULL)
>>> /* The memory allocation failed. */
>>> @@ -593,7 +593,14 @@ _dl_allocate_tls_init (void *result)
>>> some platforms use in static programs requires it. */
>>> dtv[map->l_tls_modid].pointer.val = dest;
>>>
>>> - /* Copy the initialization image and clear the BSS part. */
>>> + /* Copy the initialization image and clear the BSS part. For
>>> + audit modules or depedencies with initial-exec TLS, we can not
>>> + set the initial TLS image on default loader initialization
>>> + because it would already be set by the audit setup. However,
>>> + subsequent thread creation would need to follow the default
>>> + behaviour. */
>>> + if (__glibc_unlikely (map->l_auditing && !init_tls))
>>> + continue;
>>> memset (__mempcpy (dest, map->l_tls_initimage,
>>> map->l_tls_initimage_size), '\0',
>>> map->l_tls_blocksize - map->l_tls_initimage_size);
>>
>> I don't understand why the map->l_auditing condition is correct.
>> Shouldn't it be
>>
>> map->l_ns == LM_ID_BASE && !init_tls
Not sure if this is what I meant, the “continue” inverts the condition.
The initialization should happen for pthread_create or l_ns == LM_ID_BASE.
>> ? Everything else has been loaded via dlopen or dlmopen, so TLS
>> initialization for the main thread has already happened.
>
> This is not suffice (I tried before in fact) because we need to skip
> solely for the audit modules and dependencies at the startup. For
> instance with tst-audit21 we have with some _dl_debug_printf to
> show what is happening
>
> 1533769: [rtld.c:966] load_audit_module
> 1533769: [rtld.c:973] load_audit_module
> 1533769: [rtld.c:2465] dl_main
> 1533769: [../elf/dl-tls.c:603] map->l_name= map->l_ns=0 map->l_auditing=0 init_tls=0 [INIT]
> 1533769: [../elf/dl-tls.c:603] map->l_name=[...]/elf/tst-auditmod21a.so map->l_ns=1 map->l_auditing=1 init_tls=0
> 1533769: [../elf/dl-tls.c:603] map->l_name=[...]/libc.so.6 map->l_ns=1 map->l_auditing=1 init_tls=0
> 1533769: [../elf/dl-tls.c:603] map->l_name=[...]/libc.so.6 map->l_ns=0 map->l_auditing=0 init_tls=0 [INIT]
> 1533769: [../elf/dl-tls.c:621]
> 1533769: [rtld.c:2467] dl_main
> [allocatestack.c:435] allocate_stack
> 1533769: [../elf/dl-tls.c:633] _dl_allocate_tls
> 1533769: [../elf/dl-tls.c:603] map->l_name= map->l_ns=0 map->l_auditing=0 init_tls=1 [INIT]
> 1533769: [../elf/dl-tls.c:603] [...]/elf/tst-auditmod21a.so map->l_ns=1 map->l_auditing=1 init_tls=1 [INIT]
> 1533769: [../elf/dl-tls.c:603] [...]/libc.so.6 map->l_ns=1 map->l_auditing=1 init_tls=1 [INIT]
> 1533769: [../elf/dl-tls.c:603] [...]/libc.so.6 map->l_ns=0 map->l_auditing=0 init_tls=1 [INIT]
> 1533769: [../elf/dl-tls.c:621]
> 1533769: [../elf/dl-tls.c:642] _dl_allocate_tls
> [allocatestack.c:446] allocate_stack
>
>
> So we need to avoid initialization only for the libc.so loading by
> audit libraries, the default one should still be initialized (marked
> as [INIT]). Later when new threads are created we need to initialized
> everything.
That's what I tried to express with the LM_ID_BASE check.
Thanks,
Florian
next prev parent reply other threads:[~2022-01-18 13:02 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-17 21:31 [PATCH v10 0/4] Multiple rtld-audit fixes Adhemerval Zanella
2022-01-17 21:31 ` [PATCH v10 1/4] elf: Add la_activity during application exit Adhemerval Zanella
2022-01-18 11:29 ` Florian Weimer
2022-01-18 13:10 ` Adhemerval Zanella
2022-01-21 10:50 ` Florian Weimer
2022-01-21 10:50 ` Florian Weimer
2022-01-24 12:53 ` Adhemerval Zanella
2022-01-17 21:31 ` [PATCH v10 2/4] elf: Fix initial-exec TLS access on audit modules (BZ #28096) Adhemerval Zanella
2022-01-18 11:33 ` Florian Weimer
2022-01-18 12:58 ` Adhemerval Zanella
2022-01-18 13:02 ` Florian Weimer [this message]
2022-01-18 13:26 ` Adhemerval Zanella
2022-01-18 13:29 ` Florian Weimer
2022-01-18 13:33 ` Adhemerval Zanella
2022-01-18 13:46 ` Adhemerval Zanella
2022-01-18 13:47 ` Adhemerval Zanella
2022-01-17 21:31 ` [PATCH v10 3/4] elf: Issue la_symbind for bind-now (BZ #23734) Adhemerval Zanella
2022-01-21 11:18 ` Florian Weimer
2022-01-17 21:31 ` [PATCH v10 4/4] elf: Fix runtime linker auditing on aarch64 (BZ #26643) Adhemerval Zanella
2022-01-18 13:36 ` Szabolcs Nagy
2022-01-21 11:19 ` Florian Weimer
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