linux-kernel - Re: [PATCH v4 07/14] arm64: Add support for suppressing warning backtraces

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250318155946.GC13829@willie-the-truck>
Date: Tue, 18 Mar 2025 15:59:47 +0000
From: Will Deacon <will@...nel.org>
To: Alessandro Carminati <acarmina@...hat.com>
Cc: linux-kselftest@...r.kernel.org, David Airlie <airlied@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Maíra Canal <mcanal@...lia.com>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Kees Cook <keescook@...omium.org>,
	Daniel Diaz <daniel.diaz@...aro.org>,
	David Gow <davidgow@...gle.com>,
	Arthur Grillo <arthurgrillo@...eup.net>,
	Brendan Higgins <brendan.higgins@...ux.dev>,
	Naresh Kamboju <naresh.kamboju@...aro.org>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Maxime Ripard <mripard@...nel.org>,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Guenter Roeck <linux@...ck-us.net>,
	Alessandro Carminati <alessandro.carminati@...il.com>,
	Jani Nikula <jani.nikula@...el.com>,
	dri-devel@...ts.freedesktop.org, kunit-dev@...glegroups.com,
	linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
	linux-sh@...r.kernel.org, loongarch@...ts.linux.dev, x86@...nel.org,
	Linux Kernel Functional Testing <lkft@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH v4 07/14] arm64: Add support for suppressing warning
 backtraces

On Thu, Mar 13, 2025 at 05:40:59PM +0100, Alessandro Carminati wrote:
> On Thu, Mar 13, 2025 at 1:25 PM Will Deacon <will@...nel.org> wrote:
> >
> > On Thu, Mar 13, 2025 at 11:43:22AM +0000, Alessandro Carminati wrote:
> > > diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
> > > index 28be048db3f6..044c5e24a17d 100644
> > > --- a/arch/arm64/include/asm/bug.h
> > > +++ b/arch/arm64/include/asm/bug.h
> > > @@ -11,8 +11,14 @@
> > >
> > >  #include <asm/asm-bug.h>
> > >
> > > +#ifdef HAVE_BUG_FUNCTION
> > > +# define __BUG_FUNC  __func__
> > > +#else
> > > +# define __BUG_FUNC  NULL
> > > +#endif
> > > +
> > >  #define __BUG_FLAGS(flags)                           \
> > > -     asm volatile (__stringify(ASM_BUG_FLAGS(flags)));
> > > +     asm volatile (__stringify(ASM_BUG_FLAGS(flags, %c0)) : : "i" (__BUG_FUNC));
> >
> > Why is 'i' the right asm constraint to use here? It seems a bit odd to
> > use that for a pointer.
> 
> I received this code as legacy from a previous version.
> In my review, I considered the case when HAVE_BUG_FUNCTION is defined:
> Here, __BUG_FUNC is defined as __func__, which is the name of the
> current function as a string literal.
> Using the constraint "i" seems appropriate to me in this case.
> 
> However, when HAVE_BUG_FUNCTION is not defined:
> __BUG_FUNC is defined as NULL. Initially, I considered it literal 0,
> but after investigating your concern, I found:
> 
> ```
> $ echo -E "#include <stdio.h>\n#include <stddef.h>\nint main()
> {\nreturn 0;\n}" | aarch64-linux-gnu-gcc -E -dM - | grep NULL
> #define NULL ((void *)0)
> ```
> 
> I realized that NULL is actually a pointer that is not a link time
> symbol, and using the "i" constraint with NULL may result in undefined
> behavior.
> 
> Would the following alternative definition for __BUG_FUNC be more convincing?
> 
> ```
> #ifdef HAVE_BUG_FUNCTION
>     #define __BUG_FUNC __func__
> #else
>     #define __BUG_FUNC (uintptr_t)0
> #endif
> ```
> Let me know your thoughts.

Thanks for the analysis; I hadn't noticed this specific issue, it just
smelled a bit fishy. Anyway, the diff above looks better, thanks.

Will