From: Richard Biener <richard.guenther@gmail.com>
To: Jeff Law <law@redhat.com>,Aldy Hernandez <aldyh@redhat.com>
Cc: Martin Sebor <msebor@gmail.com>,gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: protected alloca class for malloc fallback
Date: Wed, 10 Aug 2016 18:33:00 -0000 [thread overview]
Message-ID: <283F73AD-B7CD-4389-908C-BBF479DF9101@gmail.com> (raw)
In-Reply-To: <e68d9261-a4ab-5da3-cbb6-87ad8dfb8757@redhat.com>
On August 10, 2016 8:00:20 PM GMT+02:00, Jeff Law <law@redhat.com> wrote:
>On 08/10/2016 04:04 AM, Richard Biener wrote:
>> On Tue, Aug 9, 2016 at 3:17 PM, Aldy Hernandez <aldyh@redhat.com>
>wrote:
>>> On 08/05/2016 01:55 PM, Richard Biener wrote:
>>>
>>> Hi Richard.
>>>
>>>> Please don't use std::string. For string building you can use
>obstacks.
>>>
>>>
>>> Alright let's talk details then so I can write things up in a way
>you
>>> approve of.
>>>
>>> Take for instance simple uses like all the tree_*check_failed
>routines,
>>> which I thought were great candidates for std::string-- they're
>going to be
>>> outputted to the screen or disk which is clearly many times more
>expensive
>>> than the malloc or overhead of std::string:
>>>
>>> length += strlen ("expected ");
>>> buffer = tmp = (char *) alloca (length);
>>> length = 0;
>>> while ((code = (enum tree_code) va_arg (args, int)))
>>> {
>>> const char *prefix = length ? " or " : "expected ";
>>>
>>> strcpy (tmp + length, prefix);
>>> length += strlen (prefix);
>>> strcpy (tmp + length, get_tree_code_name (code));
>>> length += strlen (get_tree_code_name (code));
>>> }
>>>
>>> Do you suggest using obstacks here, or did you have something else
>in mind?
>>
>> Why would you want to get rid of the alloca here?
>Do you know the range for LENGTH in the code above?
Yes, it's a set of tree code names.
Is it based on
>something the user could potentially control (like a variable name,
>typdef name, etc). If you don't know the length or it's possibly under
>
>the control of the user, then this can blow out the stack, which makes
>the code vulnerable to a stack shifting style attack by which further
>writes into the stack are actually writing into other parts of the
>stack, the heap, plt or some other location. Essentially this gives an
>
>attacker control over one or more stores to memory, which is often
>enough of a vulnerability to mount an attack.
Yes, I understand that. The above is not such a case. If an attacker can trick me into compiling (and possibly executing) his code then things are lost anyway. No need for a fancy buffer overflow.
IMHO the alloca case warrants for a protection on the level of the stack adjustment itself.
Richard.
>
>jeff
next prev parent reply other threads:[~2016-08-10 18:33 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-04 11:30 Aldy Hernandez
2016-08-04 12:58 ` Richard Biener
2016-08-04 15:19 ` Aldy Hernandez
2016-08-04 19:24 ` Jeff Law
2016-08-05 14:37 ` Aldy Hernandez
2016-08-05 15:15 ` Pedro Alves
2016-08-05 16:23 ` Jeff Law
2016-08-05 17:48 ` Richard Biener
2016-08-05 8:17 ` Richard Biener
2016-08-04 19:06 ` Pedro Alves
2016-08-04 19:16 ` Jeff Law
2016-08-04 19:22 ` Pedro Alves
2016-08-04 19:26 ` Jeff Law
2016-08-04 19:31 ` Pedro Alves
2016-08-05 2:10 ` Martin Sebor
2016-08-05 14:42 ` Aldy Hernandez
2016-08-05 17:56 ` Richard Biener
2016-08-05 18:16 ` Oleg Endo
2016-08-05 20:07 ` Richard Biener
2016-08-06 10:09 ` Aldy Hernandez
2016-08-06 10:15 ` Aldy Hernandez
2016-08-06 15:08 ` Richard Biener
2016-08-08 17:00 ` Jeff Law
2016-08-08 17:32 ` Trevor Saunders
2016-08-08 19:03 ` Richard Biener
2016-08-09 11:34 ` Oleg Endo
2016-08-09 17:34 ` Trevor Saunders
2016-08-10 17:03 ` Oleg Endo
2016-08-11 1:23 ` Trevor Saunders
2016-08-11 12:18 ` Oleg Endo
2016-08-11 17:55 ` Trevor Saunders
2016-08-20 2:29 ` Mike Stump
2016-08-21 20:00 ` C++11? (Re: protected alloca class for malloc fallback) Pedro Alves
2016-08-22 7:10 ` Trevor Saunders
2016-08-22 7:28 ` Richard Biener
2016-08-22 12:02 ` Eric Gallager
2016-08-22 12:58 ` Manuel López-Ibáñez
2016-08-22 22:08 ` Mike Stump
2016-08-23 23:17 ` Eric Gallager
2016-08-09 13:17 ` protected alloca class for malloc fallback Aldy Hernandez
2016-08-09 13:21 ` Bernd Schmidt
2016-08-10 10:04 ` Richard Biener
2016-08-10 10:12 ` Aldy Hernandez
2016-08-10 10:39 ` Richard Biener
2016-08-10 18:00 ` Jeff Law
2016-08-10 18:33 ` Richard Biener [this message]
2016-08-16 16:28 ` Jeff Law
2016-08-16 16:44 ` Jakub Jelinek
2016-08-16 16:47 ` Jeff Law
2016-08-16 17:54 ` Martin Sebor
2016-08-17 8:27 ` Richard Biener
2016-08-17 13:39 ` Martin Sebor
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