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From: Steven Sistare <steven.sistare@oracle.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Anthony Yznaga <anthony.yznaga@oracle.com>,
	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, ebiederm@xmission.com, 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
Subject: Re: [RFC PATCH 0/5] madvise MADV_DOEXEC
Date: Thu, 30 Jul 2020 14:27:21 -0400	[thread overview]
Message-ID: <ab7a25bf-3321-77c8-9bc3-28a223a14032@oracle.com> (raw)
In-Reply-To: <20200730174956.GK23808@casper.infradead.org>

On 7/30/2020 1:49 PM, Matthew Wilcox wrote:
> On Thu, Jul 30, 2020 at 01:35:51PM -0400, Steven Sistare wrote:
>> mshare + VA reservation is another possible solution.
>>
>> Or MADV_DOEXEC alone, which is ready now.  I hope we can get back to reviewing that.
> 
> We are.  This is the part of the review process where we explore other
> solutions to the problem.
> 
>>>> Also, we need to support updating legacy processes that already created anon segments.
>>>> We inject code that calls MADV_DOEXEC for such segments.
>>>
>>> Yes, I was assuming you'd inject code that called mshare().
>>
>> OK, mshare works on existing memory and builds a new vma.
> 
> Actually, reparents an existing VMA, and reuses the existing page tables.
> 
>>> Actually, since you're injecting code, why do you need the kernel to
>>> be involved?  You can mmap the new executable and any libraries it depends
>>> upon, set up a new stack and jump to the main() entry point, all without
>>> calling exec().  I appreciate it'd be a fair amount of code, but it'd all
>>> be in userspace and you can probably steal / reuse code from ld.so (I'm
>>> not familiar with the details of how setting up an executable is done).
>>
>> Duplicating all the work that the kernel and loader do to exec a process would
>> be error prone, require ongoing maintenance, and be redundant.  Better to define 
>> a small kernel extension and leave exec to the kernel.
> 
> Either this is a one-off kind of thing, in which case it doesn't need
> ongoing maintenance, or it's something with broad applicability, in
> which case it can live as its own userspace project.  It could even
> start off life as part of qemu and then fork into its own project.

exec will be enhanced over time in the kernel.  A separate user space implementation
would need to track that.

Reimplementing exec in userland would be a big gross mess.  Not a good solution when
we have simple and concise ways of solving the problem.

> The idea of tagging an ELF executable to say "I can cope with having
> chunks of my address space provided to me by my executor" is ... odd.

I don't disagree.  But it is useful.  We already pass a block of data containing
environment variables and arguments from one process to the next.  Preserving 
additional segments is not a big leap from there.

- Steve

  reply	other threads:[~2020-07-30 18:28 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-27 17:11 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
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 [this message]
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
2020-08-03  8:32                             ` David Laight
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
2020-08-04  8:44                     ` David Laight
2020-08-04 11:13                       ` Matthew Wilcox
2020-08-03 19:29                   ` Steven Sistare
2020-07-31 19:41 ` Steven Sistare
2021-07-08  9:52 ` Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-07-08 12:48   ` Steven Sistare

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