[PATCH] Fix __minimal_malloc segfaults in __mmap due to stack-protector

[Adhemerval Zanella]

On 16/12/2021 11:20, Stefan Liebler via Libc-alpha wrote:
> On 16/12/2021 12:54, Siddhesh Poyarekar wrote:
>> On 12/16/21 17:17, Stefan Liebler via Libc-alpha wrote:
>>> Starting with commit b05fae4d8e34604a72ee36d2d3164391b76fcf0b
>>> "elf: Use the minimal malloc on tunables_strdup",
>>> I get lots of segfaults in static tests on s390x when also using, e.g.:
>>> export GLIBC_TUNABLES="glibc.elision.enable=1"
>>>
>>> tunables_strdup callls __minimal_malloc which tries to call __mmap
>>> due to insufficient space left. __mmap itself first setups a new
>>> stack frame and segfaults when copying the stack-protector canary
>>> from thread-pointer. The latter one is not yet setup.
>>>
>>> Thus this patch also turns off stack-protection for mmap.
>>
>> LGTM.
>>
>> Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
>>
>>> ---
>>>   misc/Makefile | 4 ++++
>>>   1 file changed, 4 insertions(+)
>>>
>>> diff --git a/misc/Makefile b/misc/Makefile
>>> index 3b66cb9f6a..db40312ba9 100644
>>> --- a/misc/Makefile
>>> +++ b/misc/Makefile
>>> @@ -149,6 +149,10 @@ CFLAGS-sbrk.o = $(no-stack-protector)
>>>   CFLAGS-sbrk.op = $(no-stack-protector)
>>>   CFLAGS-brk.o = $(no-stack-protector)
>>>   CFLAGS-brk.op = $(no-stack-protector)
>>> +CFLAGS-mmap.o = $(no-stack-protector)
>>> +CFLAGS-mmap.op = $(no-stack-protector)
>>> +CFLAGS-mmap64.o = $(no-stack-protector)
>>> +CFLAGS-mmap64.op = $(no-stack-protector)
>>>     include ../Rules
>>>  
>>
> Committed.
> Thanks


Thanks for catching it, I think I have not seeing it before because I got lucky
the data segments has some slack space and not required called malloc.

Btw, do we still need to use no-stack-protector?