From: Petr Mladek <pmladek@suse.com>
To: Jane Chu <jane.chu@oracle.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.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: Tue, 18 Oct 2022 14:45:20 +0200 [thread overview]
Message-ID: <Y06f4EwisLTU0rEz@alley> (raw)
In-Reply-To: <5d987403-a7bf-8996-d639-c99edeaabcdf@oracle.com>
On Mon 2022-10-17 19:31:53, Jane Chu wrote:
> 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,
Could you please provide more details about the fixed OOB?
What exact vsprintf()/printk() call was broken and eventually
how it was fixed, please?
> the lingering issue
> is that the kernel ought to be able to protect itself, as the pointer
> contains a non-canonical address.
Was the pointer used only by the vsprintf()?
Or was it accessed also by another code, please?
I wonder if this patch would prevent the crash or if the broken
kernel would crash later anyway.
> 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.
Please, add linux-mm@kvack.org into CC. I wonder if kern_addr_valid()
is safe to use anywhere, especially during early boot. I wonder if
it would make sense to implement it on all architectures.
Best Regards,
Petr
next prev parent reply other threads:[~2022-10-18 12:45 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-17 19:16 [PATCH] vsprintf: protect kernel from panic due to non-canonical pointer dereference Jane Chu
2022-10-17 19:25 ` Andy Shevchenko
2022-10-17 19:31 ` Jane Chu
2022-10-18 12:45 ` Petr Mladek [this message]
2022-10-18 18:56 ` Jane Chu
2022-10-18 19:28 ` Randy Dunlap
2022-10-18 19:58 ` Jane Chu
2022-10-18 20:07 ` Andy Shevchenko
2022-10-18 20:30 ` Jane Chu
2022-10-18 20:49 ` Andy Shevchenko
2022-10-19 10:43 ` Haakon Bugge
2022-10-19 11:25 ` Andy Shevchenko
2022-10-19 18:36 ` Jane Chu
2022-10-19 19:26 ` Andy Shevchenko
2022-10-19 20:16 ` Jane Chu
2022-10-20 7:44 ` Petr Mladek
2022-10-20 9:18 ` Petr Mladek
2022-10-20 13:57 ` Andy Shevchenko
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