Re: [PATCH] vsprintf: protect kernel from panic due to non-canonical pointer dereference

From: Jane Chu <jane.chu@oracle.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: "pmladek@suse.com" <pmladek@suse.com>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>,
	"senozhatsky@chromium.org" <senozhatsky@chromium.org>,
	"linux@rasmusvillemoes.dk" <linux@rasmusvillemoes.dk>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] vsprintf: protect kernel from panic due to non-canonical pointer dereference
Date: Mon, 17 Oct 2022 19:31:53 +0000	[thread overview]
Message-ID: <5d987403-a7bf-8996-d639-c99edeaabcdf@oracle.com> (raw)
In-Reply-To: <Y02sENwhtpsx5yhP@smile.fi.intel.com>

On 10/17/2022 12:25 PM, Andy Shevchenko wrote:
> On Mon, Oct 17, 2022 at 01:16:11PM -0600, Jane Chu wrote:
>> While debugging a separate issue, it was found that an invalid string
>> pointer could very well contain a non-canical address, such as
>> 0x7665645f63616465. In that case, this line of defense isn't enough
>> to protect the kernel from crashing due to general protection fault
>>
>> 	if ((unsigned long)ptr < PAGE_SIZE || IS_ERR_VALUE(ptr))
>>                  return "(efault)";
>>
>> So instead, use kern_addr_valid() to validate the string pointer.
> 
> How did you check that value of the (invalid string) pointer?
> 

In the bug scenario, the invalid string pointer was an out-of-bound 
string pointer. While the OOB referencing is fixed, the lingering issue 
is that the kernel ought to be able to protect itself, as the pointer 
contains a non-canonical address.  That said, I realized that not all 
architecture implement meaningful kern_addr_valid(), so this line
    if ((unsigned long)ptr < PAGE_SIZE || IS_ERR_VALUE(ptr))
is still need.  I'll send v2.

thanks,
-jane

>