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Re: [PATCH] linux-user: mremap fails with EFAULT if address range overla
From: |
Tobias Koch |
Subject: |
Re: [PATCH] linux-user: mremap fails with EFAULT if address range overlaps with stack guard |
Date: |
Mon, 15 Jun 2020 10:17:56 +0300 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 |
Hi Laurent,
the code in musl libc probing the stack is in
https://git.musl-libc.org/cgit/musl/plain/src/thread/pthread_getattr_np.c
The setup in elfload.c does work, but only when reserved_va is not set. In that
case, any stack guard violation is
handled by the host kernel and thus results in the expected EFAULT.
However, in case of e.g. a 32bit target being emulated on a 64bit host,
reserved_va is set and the current code in
mmap.c will only produce a more generic ENOMEM, deviating from the kernel's
behavior.
On 5/7/20 5:35 PM, Laurent Vivier wrote:
> Le 05/03/2020 à 22:05, Tobias Koch a écrit :
>> If the address range starting at old_address overlaps with the stack guard it
>> is invalid and mremap must fail with EFAULT. The musl c library relies on
>> this
>> behavior to detect the stack size, which it does by doing consecutive mremaps
>> until it hits the stack guard. Without this patch, software (such as the Ruby
>> interpreter) that calls pthread_getattr_np under musl will crash on 32 bit
>> targets emulated on a 64 bit host.
> Could you share some pointers to the code that is doing this?
>
> We have already this kind of code in linux-user/elfload.c,
> setup_arg_pages(): could you check why it doesn't work?
>
> Thanks,
> Laurent
- Re: [PATCH] linux-user: mremap fails with EFAULT if address range overlaps with stack guard,
Tobias Koch <=