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From: Peter Zijlstra <peterz@infradead.org>
To: David Malcolm <dmalcolm@redhat.com>
Cc: gcc-patches@gcc.gnu.org, linux-toolchains@vger.kernel.org
Subject: Re: [PATCH 0/6] RFC: adding support to GCC for detecting trust boundaries
Date: Sun, 14 Nov 2021 00:20:47 +0100	[thread overview]
Message-ID: <20211113232047.GM174703@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20211113203732.2098220-1-dmalcolm@redhat.com>

On Sat, Nov 13, 2021 at 03:37:24PM -0500, David Malcolm wrote:

> This approach is much less expressive that the custom addres space
> approach; it would only cover the trust boundary aspect; it wouldn't
> cover any differences between generic pointers and __user, vs __iomem,
> __percpu, and __rcu which I admit I only dimly understand.

__iomem would point at device memory, which can have curious side
effects or is yet another trust boundary, depending on device and usage.

__percpu is an address space that denotes a per-cpu variable's relative
offset, it needs be combined with a per-cpu offset to get a 'real'
pointer, on x86_64 %gs segment offset is used for this purpose, other
architectures are less fortunate. The whole per_cpu()/this_cpu_*()
family of APIs accepts such pointers.

__rcu is the regular kernel address space, but denotes that the object
pointed to has RCU lifetime management. The attribute is laundered
through rcu_dereference() to remove the __rcu qualifier.

> Possibly silly question: is it always a bug for the value of a kernel
> pointer to leak into user space?  i.e. should I be complaining about an
> infoleak if the value of a trusted_ptr itself is written to
> *untrusted_ptr?  e.g.

Yes, always. Leaking kernel pointers is unconditionally bad.

  parent reply	other threads:[~2021-11-13 23:20 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-13 20:37 [PATCH 0/6] RFC: adding support to GCC for detecting trust boundaries David Malcolm
2021-11-13 20:37 ` [PATCH 1a/6] RFC: Implement "#pragma GCC custom_address_space" David Malcolm
2021-11-13 20:37 ` [PATCH 1b/6] Add __attribute__((untrusted)) David Malcolm
2021-12-09 22:54   ` Martin Sebor
2022-01-06 15:10     ` David Malcolm
2022-01-06 18:59       ` Martin Sebor
2021-11-13 20:37 ` [PATCH 2/6] Add returns_zero_on_success/failure attributes David Malcolm
2021-11-15  7:03   ` Prathamesh Kulkarni
2021-11-15 14:45     ` Peter Zijlstra
2021-11-15 22:30       ` David Malcolm
2021-11-15 22:12     ` David Malcolm
2021-11-17  9:23       ` Prathamesh Kulkarni
2021-11-17 22:43         ` Joseph Myers
2021-11-18 20:08           ` Segher Boessenkool
2021-11-18 23:45             ` David Malcolm
2021-11-19 21:52               ` Segher Boessenkool
2021-11-18 23:34           ` David Malcolm
2021-12-06 18:34             ` Martin Sebor
2021-11-18 23:15         ` David Malcolm
2021-11-13 20:37 ` [PATCH 4a/6] analyzer: implement region::untrusted_p in terms of custom address spaces David Malcolm
2021-11-13 20:37 ` [PATCH 4b/6] analyzer: implement region::untrusted_p in terms of __attribute__((untrusted)) David Malcolm
2021-11-13 20:37 ` [PATCH 5/6] analyzer: use region::untrusted_p in taint detection David Malcolm
2021-11-13 20:37 ` [PATCH 6/6] Add __attribute__ ((tainted)) David Malcolm
2022-01-06 14:08   ` PING (C/C++): " David Malcolm
2022-01-10 21:36     ` PING^2 " David Malcolm
2022-01-12  4:36       ` Jason Merrill
2022-01-12 15:33         ` David Malcolm
2022-01-13 19:08           ` Jason Merrill
2022-01-14  1:25             ` [committed] Add __attribute__ ((tainted_args)) David Malcolm
2021-11-13 23:20 ` Peter Zijlstra [this message]
2021-11-14  2:54   ` [PATCH 0/6] RFC: adding support to GCC for detecting trust boundaries David Malcolm
2021-11-14 13:54 ` Miguel Ojeda
2021-12-06 18:12 ` Martin Sebor
2021-12-06 19:40   ` Segher Boessenkool
2021-12-09  0:06     ` David Malcolm
2021-12-09  0:41       ` Segher Boessenkool
2021-12-09 16:42     ` Martin Sebor
2021-12-09 23:40       ` Segher Boessenkool
2021-12-08 23:11   ` David Malcolm

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