linux-hardening - Re: [linux-next:master] [kbuild] df8fc4e934: BUG:unable_to_handle_page_fault_for

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Date:   Tue, 13 Jun 2023 13:46:54 -0700
From:   Kees Cook <keescook@...omium.org>
To:     kernel test robot <oliver.sang@...el.com>
Cc:     oe-lkp@...ts.linux.dev, lkp@...el.com,
        Linux Memory Management List <linux-mm@...ck.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev,
        linux-hardening@...r.kernel.org
Subject: Re: [linux-next:master] [kbuild]  df8fc4e934:
 BUG:unable_to_handle_page_fault_for_address

On Sun, Jun 11, 2023 at 09:41:30PM +0800, kernel test robot wrote:
> the issue we found below is by clang-15, but we confirmed clang-15 we use is
> commit 8dfdcc7b7b in llvm-project. it supports the flag already.

Interesting! Thanks for the report.

> [  228.605608][    C1] BUG: unable to handle page fault for address: 04090300
> [...]
> [ 228.608262][ C1] EIP: string (lib/vsprintf.c:644 lib/vsprintf.c:726) 
> [...]
> [ 228.608262][ C1] Call Trace:
> [ 228.608262][ C1]  <SOFTIRQ>
> [ 228.608262][ C1] vsnprintf (lib/vsprintf.c:2817) 
> [ 228.608262][ C1] vprintk_store (kernel/printk/printk.c:2191) 
> [ 228.608262][ C1] vprintk_emit (kernel/printk/printk.c:2288) 
> [ 228.608262][ C1] vprintk_default (kernel/printk/printk.c:2318) 
> [ 228.608262][ C1] vprintk (kernel/printk/printk_safe.c:50) 
> [ 228.608262][ C1] _printk (kernel/printk/printk.c:2331) 
> [ 228.608262][ C1] __ubsan_handle_out_of_bounds (lib/ubsan.c:209 lib/ubsan.c:343) 

This is a crash within the UBSAN handler! That's very unexpected.

> [ 228.608262][ C1] get_string (drivers/usb/gadget/composite.c:1314) 
> [ 228.608262][ C1] composite_setup (drivers/usb/gadget/composite.c:1871) 
> [ 228.608262][ C1] dummy_timer (drivers/usb/gadget/udc/dummy_hcd.c:?) 

And the out-of-bounds condition got triggered in dummy_hcd.

I also see this is happening in SOFTIRQ context. I wonder if there is a
problem with UBSAN vs SOFTIRQ. Again, I'd find that surprising...

I'll see what I can find...

-- 
Kees Cook