* Possible glibc 2.35 ARM regression in LD_BIND_NOT
@ 2022-07-04 19:14 Nathan Nye
2022-07-04 19:31 ` Nathan Nye
0 siblings, 1 reply; 4+ messages in thread
From: Nathan Nye @ 2022-07-04 19:14 UTC (permalink / raw)
To: libc-help
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Good afternoon,
I'm reviewing what could be a regression in LD_BIND_NOT's functionality
in glibc 2.35 on ARM architectures (there were a few recent ARM audit
changes). Symbol binding only occurs a single time on glibc 2.35/ARM,
even when LD_BIND_NOT is enabled. I've tested:
* Ubuntu 22.04 x86_64 glibc 2.35
* Ubuntu 20.04 ARM glibc 2.34
* Ubuntu 22.04 ARM glibc 2.35
I could use a second pair of eyes on this issue to verify it exists.
Here is the test case I cobbled together, please excuse the poor C code
I wrote while testing: https://pastebin.com/raw/HSSYjemj
I've also attached the test case to this email. Thanks!
Very respectfully,
Nathan Nye
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runevp.c:
// gcc runevp.c -o runevp
#include <stdio.h>
#include <unistd.h>
int main() {
int i;
for (i=0; i < 5; i++) {
if(fork()==0) {
execvp("true", NULL);
}
}
return 0;
}
auditlib.c:
// gcc -Wall -fPIC -shared -o auditlib.so auditlib.c
#include <link.h>
#include <stdio.h>
typedef long int Lmid_t;
unsigned int la_version(unsigned int version) { return version; }
unsigned int la_objopen(struct link_map *map, Lmid_t lmid, uintptr_t *cookie) { return 3; }
uintptr_t la_symbind64(Elf64_Sym *sym, unsigned int ndx, uintptr_t *refcook, uintptr_t *defcook, unsigned int *flags, const char *symname) {
if (strcmp(symname, "execvp") == 0) {
printf("symbol binding for '%s'\n", symname);
}
return sym->st_value;
}
Any glibc release except glibc 2.35 on ARM: Symbol binding occurs repeatedly (LD_BIND_NOT)
$ LD_AUDIT=/path/to/auditlib.so LD_BIND_NOT=1 ./runevp
symbol binding for 'execvp'
symbol binding for 'execvp'
symbol binding for 'execvp'
symbol binding for 'execvp'
symbol binding for 'execvp'
glibc 2.35 on ARM: Symbol binding occurs once (ignores LD_BIND_NOT)
$ LD_AUDIT=/path/to/auditlib.so LD_BIND_NOT=1 ./runevp
symbol binding for 'execvp'
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Possible glibc 2.35 ARM regression in LD_BIND_NOT
2022-07-04 19:14 Possible glibc 2.35 ARM regression in LD_BIND_NOT Nathan Nye
@ 2022-07-04 19:31 ` Nathan Nye
2022-07-05 14:34 ` Nathan Nye
0 siblings, 1 reply; 4+ messages in thread
From: Nathan Nye @ 2022-07-04 19:31 UTC (permalink / raw)
To: libc-help
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+Adhemerval
Hi Adhemerval,
I think you may know the relevant source best if this issue exists. Your
feedback would be really valuable if you're able to test it.
Very respectfully,
Nathan Nye
On 7/4/22 3:14 PM, Nathan Nye wrote:
> Good afternoon,
>
> I'm reviewing what could be a regression in LD_BIND_NOT's
> functionality in glibc 2.35 on ARM architectures (there were a few
> recent ARM audit changes). Symbol binding only occurs a single time on
> glibc 2.35/ARM, even when LD_BIND_NOT is enabled. I've tested:
>
> * Ubuntu 22.04 x86_64 glibc 2.35
> * Ubuntu 20.04 ARM glibc 2.34
> * Ubuntu 22.04 ARM glibc 2.35
>
> I could use a second pair of eyes on this issue to verify it exists.
> Here is the test case I cobbled together, please excuse the poor C
> code I wrote while testing: https://pastebin.com/raw/HSSYjemj
>
> I've also attached the test case to this email. Thanks!
>
> Very respectfully,
> Nathan Nye
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Possible glibc 2.35 ARM regression in LD_BIND_NOT
2022-07-04 19:31 ` Nathan Nye
@ 2022-07-05 14:34 ` Nathan Nye
2022-07-05 17:04 ` Adhemerval Zanella
0 siblings, 1 reply; 4+ messages in thread
From: Nathan Nye @ 2022-07-05 14:34 UTC (permalink / raw)
To: libc-help
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All,
I isolated the issue. When compiling binaries using gcc on Ubuntu 20.04
or below, the resulting binary does not have PIE - regardless of the
-pie argument being passed to the compiler. Ubuntu 22.04 correctly
reflects the default build flags being PIE and the binaries have PIE
unless the arguments passed to gcc include -no-pie.
Thanks,
Nathan Nye
On 7/4/22 3:31 PM, Nathan Nye wrote:
> +Adhemerval
>
> Hi Adhemerval,
>
> I think you may know the relevant source best if this issue exists.
> Your feedback would be really valuable if you're able to test it.
>
> Very respectfully,
> Nathan Nye
>
> On 7/4/22 3:14 PM, Nathan Nye wrote:
>> Good afternoon,
>>
>> I'm reviewing what could be a regression in LD_BIND_NOT's
>> functionality in glibc 2.35 on ARM architectures (there were a few
>> recent ARM audit changes). Symbol binding only occurs a single time
>> on glibc 2.35/ARM, even when LD_BIND_NOT is enabled. I've tested:
>>
>> * Ubuntu 22.04 x86_64 glibc 2.35
>> * Ubuntu 20.04 ARM glibc 2.34
>> * Ubuntu 22.04 ARM glibc 2.35
>>
>> I could use a second pair of eyes on this issue to verify it exists.
>> Here is the test case I cobbled together, please excuse the poor C
>> code I wrote while testing: https://pastebin.com/raw/HSSYjemj
>>
>> I've also attached the test case to this email. Thanks!
>>
>> Very respectfully,
>> Nathan Nye
>
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Possible glibc 2.35 ARM regression in LD_BIND_NOT
2022-07-05 14:34 ` Nathan Nye
@ 2022-07-05 17:04 ` Adhemerval Zanella
0 siblings, 0 replies; 4+ messages in thread
From: Adhemerval Zanella @ 2022-07-05 17:04 UTC (permalink / raw)
To: Nathan Nye; +Cc: libc-help
> On 5 Jul 2022, at 11:34, Nathan Nye <nnye@whitebeamsec.com> wrote:
>
> All,
>
> I isolated the issue. When compiling binaries using gcc on Ubuntu 20.04 or below, the resulting binary does not have PIE - regardless of the -pie argument being passed to the compiler. Ubuntu 22.04 correctly reflects the default build flags being PIE and the binaries have PIE unless the arguments passed to gcc include -no-pie.
>
> Thanks,
> Nathan Nye
The problem is not in fact PIE, but rather that newer toolchain default to
bindnow. Using the provided example on
* Ubuntu 14 (glibc 2.19), Ubuntu 16 (glibc 2.23), and Ubuntu 18 (glibc 2.27)
$ gcc -Wall runevp.c -o runevp -Wl,-z,lazy
$ gcc -Wall -fPIC -shared -o auditlib.so auditlib.c
$ LD_AUDIT=./auditlib.so LD_BIND_NOT=1 LD_BIND_NOW=1 ./runevp
$
* And on Ubuntu 22.04 (glibc 2.35)
$ gcc -Wall runevp.c -o runevp -Wl,-z,lazy
$ gcc -Wall -fPIC -shared -o auditlib.so auditlib.c
$ LD_AUDIT=./auditlib.so LD_BIND_NOT=1 LD_BIND_NOW=1 ./runevp
symbol binding for ‘execvp'
On glibc 2.34 we now see a bind-now la_symbind event, different than
previous version. If you build with -Wl,-z,lazy we will see the previous
behavior where la_symbind will be called on each symbol resolution.
Now for LD_BIND_NOT and bind-now, I think this is the correct behavior:
we need to always update the GOT entry since runtime won’t setup a
lazy resolution PLT entry (symbols resolution is always setup at
startup phase). Otherwise we will need to add a hack similar to
LD_PROFILE and I really don’t think this is the best strategy.
>
> On 7/4/22 3:31 PM, Nathan Nye wrote:
>> +Adhemerval
>>
>> Hi Adhemerval,
>>
>> I think you may know the relevant source best if this issue exists. Your feedback would be really valuable if you're able to test it.
>>
>> Very respectfully,
>> Nathan Nye
>>
>> On 7/4/22 3:14 PM, Nathan Nye wrote:
>>> Good afternoon,
>>>
>>> I'm reviewing what could be a regression in LD_BIND_NOT's functionality in glibc 2.35 on ARM architectures (there were a few recent ARM audit changes). Symbol binding only occurs a single time on glibc 2.35/ARM, even when LD_BIND_NOT is enabled. I've tested:
>>> • Ubuntu 22.04 x86_64 glibc 2.35
>>> • Ubuntu 20.04 ARM glibc 2.34
>>> • Ubuntu 22.04 ARM glibc 2.35
>>> I could use a second pair of eyes on this issue to verify it exists. Here is the test case I cobbled together, please excuse the poor C code I wrote while testing: https://pastebin.com/raw/HSSYjemj
>>>
>>> I've also attached the test case to this email. Thanks!
>>>
>>> Very respectfully,
>>> Nathan Nye
>>
>
> <OpenPGP_0xCB7269934F16882E.asc>
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2022-07-04 19:14 Possible glibc 2.35 ARM regression in LD_BIND_NOT Nathan Nye
2022-07-04 19:31 ` Nathan Nye
2022-07-05 14:34 ` Nathan Nye
2022-07-05 17:04 ` Adhemerval Zanella
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