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From: Anthony Yznaga <anthony.yznaga@oracle.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	mhocko@kernel.org, tglx@linutronix.de, mingo@redhat.com,
	bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	viro@zeniv.linux.org.uk, akpm@linux-foundation.org,
	arnd@arndb.de, keescook@chromium.org, gerg@linux-m68k.org,
	ktkhai@virtuozzo.com, christian.brauner@ubuntu.com,
	peterz@infradead.org, esyr@redhat.com, jgg@ziepe.ca,
	christian@kellner.me, areber@redhat.com, cyphar@cyphar.com,
	steven.sistare@oracle.com
Subject: Re: [RFC PATCH 3/5] mm: introduce VM_EXEC_KEEP
Date: Tue, 28 Jul 2020 10:44:13 -0700
Message-ID: <7694af9d-dfb9-8c44-dc41-79f58bb14413@oracle.com> (raw)
In-Reply-To: <87365bg3nx.fsf@x220.int.ebiederm.org>



On 7/28/20 6:38 AM, ebiederm@xmission.com wrote:
> Anthony Yznaga <anthony.yznaga@oracle.com> writes:
>
>> A vma with the VM_EXEC_KEEP flag is preserved across exec.  For anonymous
>> vmas only.  For safety, overlap with fixed address VMAs created in the new
>> mm during exec (e.g. the stack and elf load segments) is not permitted and
>> will cause the exec to fail.
>> (We are studying how to guarantee there are no conflicts. Comments welcome.)
>>
>> diff --git a/fs/exec.c b/fs/exec.c
>> index 262112e5f9f8..1de09c4eef00 100644
>> --- a/fs/exec.c
>> +++ b/fs/exec.c
>> @@ -1069,6 +1069,20 @@ ssize_t read_code(struct file *file, unsigned long addr, loff_t pos, size_t len)
>>  EXPORT_SYMBOL(read_code);
>>  #endif
>>  
>> +static int vma_dup_some(struct mm_struct *old_mm, struct mm_struct *new_mm)
>> +{
>> +	struct vm_area_struct *vma;
>> +	int ret;
>> +
>> +	for (vma = old_mm->mmap; vma; vma = vma->vm_next)
>> +		if (vma->vm_flags & VM_EXEC_KEEP) {
>> +			ret = vma_dup(vma, new_mm);
>> +			if (ret)
>> +				return ret;
>> +		}
>> +	return 0;
>> +}
>> +
>>  /*
>>   * Maps the mm_struct mm into the current task struct.
>>   * On success, this function returns with the mutex
>> @@ -1104,6 +1118,12 @@ static int exec_mmap(struct mm_struct *mm)
>>  			mutex_unlock(&tsk->signal->exec_update_mutex);
>>  			return -EINTR;
>>  		}
>> +		ret = vma_dup_some(old_mm, mm);
>                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Ouch! An unconditional loop through all of the vmas of the execing
> process, just in case there is a VM_EXEC_KEEP vma.
>
> I know we already walk the list in exit_mmap, but I get the feeling this
> will slow exec down when this feature is not enabled, especially when
> a process with a lot of vmas is calling exec.
Patch 4 changes this to only call vma_dup_some() if the new
binary has opted in to accepting preserved memory.

Anthony
>
>                 
>> +		if (ret) {
>> +			mmap_read_unlock(old_mm);
>> +			mutex_unlock(&tsk->signal->exec_update_mutex);
>> +			return ret;
>> +		}
>>  	}
>>  
>>  	task_lock(tsk);



  reply index

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-27 17:11 [RFC PATCH 0/5] madvise MADV_DOEXEC Anthony Yznaga
2020-07-27 17:07 ` Eric W. Biederman
2020-07-27 18:00   ` Steven Sistare
2020-07-28 13:40     ` Christian Brauner
2020-07-27 17:11 ` [RFC PATCH 1/5] elf: reintroduce using MAP_FIXED_NOREPLACE for elf executable mappings Anthony Yznaga
2020-07-27 17:11 ` [RFC PATCH 2/5] mm: do not assume only the stack vma exists in setup_arg_pages() Anthony Yznaga
2020-07-27 17:11 ` [RFC PATCH 3/5] mm: introduce VM_EXEC_KEEP Anthony Yznaga
2020-07-28 13:38   ` Eric W. Biederman
2020-07-28 17:44     ` Anthony Yznaga [this message]
2020-07-29 13:52   ` Kirill A. Shutemov
2020-07-29 23:20     ` Anthony Yznaga
2020-07-27 17:11 ` [RFC PATCH 4/5] exec, elf: require opt-in for accepting preserved mem Anthony Yznaga
2020-07-27 17:11 ` [RFC PATCH 5/5] mm: introduce MADV_DOEXEC Anthony Yznaga
2020-07-28 13:22   ` Kirill Tkhai
2020-07-28 14:06     ` Steven Sistare
2020-07-28 11:34 ` [RFC PATCH 0/5] madvise MADV_DOEXEC Kirill Tkhai
2020-07-28 17:28   ` Anthony Yznaga
2020-07-28 14:23 ` Andy Lutomirski
2020-07-28 14:30   ` Steven Sistare
2020-07-30 15:22 ` Matthew Wilcox
2020-07-30 15:27   ` Christian Brauner
2020-07-30 15:34     ` Matthew Wilcox
2020-07-30 15:54       ` Christian Brauner
2020-07-31  9:12     ` Stefan Hajnoczi
2020-07-30 15:59   ` Steven Sistare
2020-07-30 17:12     ` Matthew Wilcox
2020-07-30 17:35       ` Steven Sistare
2020-07-30 17:49         ` Matthew Wilcox
2020-07-30 18:27           ` Steven Sistare
2020-07-30 21:58             ` Eric W. Biederman
2020-07-31 14:57               ` Steven Sistare
2020-07-31 15:27                 ` Matthew Wilcox
2020-07-31 16:11                   ` Steven Sistare
2020-07-31 16:56                     ` Jason Gunthorpe
2020-07-31 17:15                       ` Steven Sistare
2020-07-31 17:48                         ` Jason Gunthorpe
2020-07-31 17:55                           ` Steven Sistare
2020-07-31 17:23                     ` Matthew Wilcox
2020-08-03 15:28                 ` Eric W. Biederman
2020-08-03 15:42                   ` James Bottomley
2020-08-03 20:03                     ` Steven Sistare
     [not found]                     ` <9371b8272fd84280ae40b409b260bab3@AcuMS.aculab.com>
2020-08-04 11:13                       ` Matthew Wilcox
2020-08-03 19:29                   ` Steven Sistare
2020-07-31 19:41 ` Steven Sistare

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