* [PATCH] arm: Remove unused ldr _dl_start_user
@ 2024-02-05 16:18 Adhemerval Zanella
2024-02-05 17:06 ` Szabolcs Nagy
2024-02-05 17:13 ` Sam James
0 siblings, 2 replies; 6+ messages in thread
From: Adhemerval Zanella @ 2024-02-05 16:18 UTC (permalink / raw)
To: libc-alpha; +Cc: Adrian Ratiu
The commit 49d877a80b29d3002887b084eec6676d9f5fec18 (arm: Remove
_dl_skip_args usage) removed the _SKIP_ARGS literal, which was
previously loader to r4 on loader _start. However, the cleanup did not
remove the following 'ldr r4, [sl, r4]' on _dl_start_user, used to check
to skip the arguments after ld self-relocations.
In my testing, the kernel initially set r4 to 0, which makes the
ldr instruction just read the _GLOBAL_OFFSET_TABLE_. However, since r4
is a caller-saved register; a different runtime might not zero
initialize it and thus trigger an invalid memory access.
Checked on arm-linux-gnu.
Reported-by: Adrian Ratiu <adrian.ratiu@collabora.com>
---
sysdeps/arm/dl-machine.h | 1 -
1 file changed, 1 deletion(-)
diff --git a/sysdeps/arm/dl-machine.h b/sysdeps/arm/dl-machine.h
index b857bbc868..dd1a0f6b6e 100644
--- a/sysdeps/arm/dl-machine.h
+++ b/sysdeps/arm/dl-machine.h
@@ -139,7 +139,6 @@ _start:\n\
_dl_start_user:\n\
adr r6, .L_GET_GOT\n\
add sl, sl, r6\n\
- ldr r4, [sl, r4]\n\
@ save the entry point in another register\n\
mov r6, r0\n\
@ get the original arg count\n\
--
2.34.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] arm: Remove unused ldr _dl_start_user
2024-02-05 16:18 [PATCH] arm: Remove unused ldr _dl_start_user Adhemerval Zanella
@ 2024-02-05 17:06 ` Szabolcs Nagy
2024-02-05 17:08 ` Adhemerval Zanella Netto
2024-02-05 17:13 ` Sam James
1 sibling, 1 reply; 6+ messages in thread
From: Szabolcs Nagy @ 2024-02-05 17:06 UTC (permalink / raw)
To: Adhemerval Zanella, libc-alpha; +Cc: Adrian Ratiu
The 02/05/2024 16:18, Adhemerval Zanella wrote:
> The commit 49d877a80b29d3002887b084eec6676d9f5fec18 (arm: Remove
> _dl_skip_args usage) removed the _SKIP_ARGS literal, which was
> previously loader to r4 on loader _start. However, the cleanup did not
> remove the following 'ldr r4, [sl, r4]' on _dl_start_user, used to check
> to skip the arguments after ld self-relocations.
>
> In my testing, the kernel initially set r4 to 0, which makes the
> ldr instruction just read the _GLOBAL_OFFSET_TABLE_. However, since r4
> is a caller-saved register; a different runtime might not zero
^^^^^^
it's callee-saved (preserved by calls)
> initialize it and thus trigger an invalid memory access.
>
> Checked on arm-linux-gnu.
patch looks good.
Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
>
> Reported-by: Adrian Ratiu <adrian.ratiu@collabora.com>
> ---
> sysdeps/arm/dl-machine.h | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/sysdeps/arm/dl-machine.h b/sysdeps/arm/dl-machine.h
> index b857bbc868..dd1a0f6b6e 100644
> --- a/sysdeps/arm/dl-machine.h
> +++ b/sysdeps/arm/dl-machine.h
> @@ -139,7 +139,6 @@ _start:\n\
> _dl_start_user:\n\
> adr r6, .L_GET_GOT\n\
> add sl, sl, r6\n\
> - ldr r4, [sl, r4]\n\
> @ save the entry point in another register\n\
> mov r6, r0\n\
> @ get the original arg count\n\
> --
> 2.34.1
>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] arm: Remove unused ldr _dl_start_user
2024-02-05 17:06 ` Szabolcs Nagy
@ 2024-02-05 17:08 ` Adhemerval Zanella Netto
0 siblings, 0 replies; 6+ messages in thread
From: Adhemerval Zanella Netto @ 2024-02-05 17:08 UTC (permalink / raw)
To: Szabolcs Nagy, libc-alpha; +Cc: Adrian Ratiu
On 05/02/24 14:06, Szabolcs Nagy wrote:
> The 02/05/2024 16:18, Adhemerval Zanella wrote:
>> The commit 49d877a80b29d3002887b084eec6676d9f5fec18 (arm: Remove
>> _dl_skip_args usage) removed the _SKIP_ARGS literal, which was
>> previously loader to r4 on loader _start. However, the cleanup did not
>> remove the following 'ldr r4, [sl, r4]' on _dl_start_user, used to check
>> to skip the arguments after ld self-relocations.
>>
>> In my testing, the kernel initially set r4 to 0, which makes the
>> ldr instruction just read the _GLOBAL_OFFSET_TABLE_. However, since r4
>> is a caller-saved register; a different runtime might not zero
> ^^^^^^
>
> it's callee-saved (preserved by calls)
Yeah, I meant calee-saved indeed. I will fix the commit message.
>
>> initialize it and thus trigger an invalid memory access.
>>
>> Checked on arm-linux-gnu.
>
> patch looks good.
>
> Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
>
>>
>> Reported-by: Adrian Ratiu <adrian.ratiu@collabora.com>
>> ---
>> sysdeps/arm/dl-machine.h | 1 -
>> 1 file changed, 1 deletion(-)
>>
>> diff --git a/sysdeps/arm/dl-machine.h b/sysdeps/arm/dl-machine.h
>> index b857bbc868..dd1a0f6b6e 100644
>> --- a/sysdeps/arm/dl-machine.h
>> +++ b/sysdeps/arm/dl-machine.h
>> @@ -139,7 +139,6 @@ _start:\n\
>> _dl_start_user:\n\
>> adr r6, .L_GET_GOT\n\
>> add sl, sl, r6\n\
>> - ldr r4, [sl, r4]\n\
>> @ save the entry point in another register\n\
>> mov r6, r0\n\
>> @ get the original arg count\n\
>> --
>> 2.34.1
>>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] arm: Remove unused ldr _dl_start_user
2024-02-05 16:18 [PATCH] arm: Remove unused ldr _dl_start_user Adhemerval Zanella
2024-02-05 17:06 ` Szabolcs Nagy
@ 2024-02-05 17:13 ` Sam James
2024-02-05 18:09 ` Adhemerval Zanella Netto
1 sibling, 1 reply; 6+ messages in thread
From: Sam James @ 2024-02-05 17:13 UTC (permalink / raw)
To: Adhemerval Zanella; +Cc: Adrian Ratiu, libc-alpha
Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:
> The commit 49d877a80b29d3002887b084eec6676d9f5fec18 (arm: Remove
> _dl_skip_args usage) removed the _SKIP_ARGS literal, which was
> previously loader to r4 on loader _start. However, the cleanup did not
> remove the following 'ldr r4, [sl, r4]' on _dl_start_user, used to check
> to skip the arguments after ld self-relocations.
>
> In my testing, the kernel initially set r4 to 0, which makes the
> ldr instruction just read the _GLOBAL_OFFSET_TABLE_. However, since r4
> is a caller-saved register; a different runtime might not zero
> initialize it and thus trigger an invalid memory access.
Tag the bug?
Also, I feel like the title perhaps makes the change sound more cosmetic
than it is.
>
> Checked on arm-linux-gnu.
>
> Reported-by: Adrian Ratiu <adrian.ratiu@collabora.com>
> ---
> sysdeps/arm/dl-machine.h | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/sysdeps/arm/dl-machine.h b/sysdeps/arm/dl-machine.h
> index b857bbc868..dd1a0f6b6e 100644
> --- a/sysdeps/arm/dl-machine.h
> +++ b/sysdeps/arm/dl-machine.h
> @@ -139,7 +139,6 @@ _start:\n\
> _dl_start_user:\n\
> adr r6, .L_GET_GOT\n\
> add sl, sl, r6\n\
> - ldr r4, [sl, r4]\n\
> @ save the entry point in another register\n\
> mov r6, r0\n\
> @ get the original arg count\n\
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] arm: Remove unused ldr _dl_start_user
2024-02-05 17:13 ` Sam James
@ 2024-02-05 18:09 ` Adhemerval Zanella Netto
2024-02-05 18:19 ` Sam James
0 siblings, 1 reply; 6+ messages in thread
From: Adhemerval Zanella Netto @ 2024-02-05 18:09 UTC (permalink / raw)
To: Sam James; +Cc: Adrian Ratiu, libc-alpha
On 05/02/24 14:13, Sam James wrote:
>
> Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:
>
>> The commit 49d877a80b29d3002887b084eec6676d9f5fec18 (arm: Remove
>> _dl_skip_args usage) removed the _SKIP_ARGS literal, which was
>> previously loader to r4 on loader _start. However, the cleanup did not
>> remove the following 'ldr r4, [sl, r4]' on _dl_start_user, used to check
>> to skip the arguments after ld self-relocations.
>>
>> In my testing, the kernel initially set r4 to 0, which makes the
>> ldr instruction just read the _GLOBAL_OFFSET_TABLE_. However, since r4
>> is a caller-saved register; a different runtime might not zero
>> initialize it and thus trigger an invalid memory access.
>
> Tag the bug?
>
> Also, I feel like the title perhaps makes the change sound more cosmetic
> than it is.
Right, I will change to 'arm: Remove wrong ldr _dl_start_user (BZ 31339)'
>
>>
>> Checked on arm-linux-gnu.
>>
>> Reported-by: Adrian Ratiu <adrian.ratiu@collabora.com>
>> ---
>> sysdeps/arm/dl-machine.h | 1 -
>> 1 file changed, 1 deletion(-)
>>
>> diff --git a/sysdeps/arm/dl-machine.h b/sysdeps/arm/dl-machine.h
>> index b857bbc868..dd1a0f6b6e 100644
>> --- a/sysdeps/arm/dl-machine.h
>> +++ b/sysdeps/arm/dl-machine.h
>> @@ -139,7 +139,6 @@ _start:\n\
>> _dl_start_user:\n\
>> adr r6, .L_GET_GOT\n\
>> add sl, sl, r6\n\
>> - ldr r4, [sl, r4]\n\
>> @ save the entry point in another register\n\
>> mov r6, r0\n\
>> @ get the original arg count\n\
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] arm: Remove unused ldr _dl_start_user
2024-02-05 18:09 ` Adhemerval Zanella Netto
@ 2024-02-05 18:19 ` Sam James
0 siblings, 0 replies; 6+ messages in thread
From: Sam James @ 2024-02-05 18:19 UTC (permalink / raw)
To: Adhemerval Zanella Netto; +Cc: Sam James, Adrian Ratiu, libc-alpha
Adhemerval Zanella Netto <adhemerval.zanella@linaro.org> writes:
> On 05/02/24 14:13, Sam James wrote:
>>
>> Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:
>>
>>> The commit 49d877a80b29d3002887b084eec6676d9f5fec18 (arm: Remove
>>> _dl_skip_args usage) removed the _SKIP_ARGS literal, which was
>>> previously loader to r4 on loader _start. However, the cleanup did not
>>> remove the following 'ldr r4, [sl, r4]' on _dl_start_user, used to check
>>> to skip the arguments after ld self-relocations.
>>>
>>> In my testing, the kernel initially set r4 to 0, which makes the
>>> ldr instruction just read the _GLOBAL_OFFSET_TABLE_. However, since r4
>>> is a caller-saved register; a different runtime might not zero
>>> initialize it and thus trigger an invalid memory access.
>>
>> Tag the bug?
>>
>> Also, I feel like the title perhaps makes the change sound more cosmetic
>> than it is.
>
> Right, I will change to 'arm: Remove wrong ldr _dl_start_user (BZ 31339)'
wfm, thanks!
>
>>
>>>
>>> Checked on arm-linux-gnu.
>>>
>>> Reported-by: Adrian Ratiu <adrian.ratiu@collabora.com>
>>> ---
>>> sysdeps/arm/dl-machine.h | 1 -
>>> 1 file changed, 1 deletion(-)
>>>
>>> diff --git a/sysdeps/arm/dl-machine.h b/sysdeps/arm/dl-machine.h
>>> index b857bbc868..dd1a0f6b6e 100644
>>> --- a/sysdeps/arm/dl-machine.h
>>> +++ b/sysdeps/arm/dl-machine.h
>>> @@ -139,7 +139,6 @@ _start:\n\
>>> _dl_start_user:\n\
>>> adr r6, .L_GET_GOT\n\
>>> add sl, sl, r6\n\
>>> - ldr r4, [sl, r4]\n\
>>> @ save the entry point in another register\n\
>>> mov r6, r0\n\
>>> @ get the original arg count\n\
>>
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2024-02-05 18:19 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2024-02-05 16:18 [PATCH] arm: Remove unused ldr _dl_start_user Adhemerval Zanella
2024-02-05 17:06 ` Szabolcs Nagy
2024-02-05 17:08 ` Adhemerval Zanella Netto
2024-02-05 17:13 ` Sam James
2024-02-05 18:09 ` Adhemerval Zanella Netto
2024-02-05 18:19 ` Sam James
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).