Date: Wed, 10 Jun 2020 08:30:47 +0100 From: Will Deacon <will@...nel.org> To: Kees Cook <keescook@...omium.org> Cc: Alexander Popov <alex.popov@...ux.com>, Emese Revfy <re.emese@...il.com>, Miguel Ojeda <miguel.ojeda.sandonis@...il.com>, Masahiro Yamada <masahiroy@...nel.org>, Michal Marek <michal.lkml@...kovi.net>, Andrew Morton <akpm@...ux-foundation.org>, Masahiro Yamada <yamada.masahiro@...ionext.com>, Thiago Jung Bauermann <bauerman@...ux.ibm.com>, Luis Chamberlain <mcgrof@...nel.org>, Jessica Yu <jeyu@...nel.org>, Sven Schnelle <svens@...ckframe.org>, Iurii Zaikin <yzaikin@...gle.com>, Catalin Marinas <catalin.marinas@....com>, Vincenzo Frascino <vincenzo.frascino@....com>, Thomas Gleixner <tglx@...utronix.de>, Peter Collingbourne <pcc@...gle.com>, Naohiro Aota <naohiro.aota@....com>, Alexander Monakov <amonakov@...ras.ru>, Mathias Krause <minipli@...glemail.com>, PaX Team <pageexec@...email.hu>, Brad Spengler <spender@...ecurity.net>, Laura Abbott <labbott@...hat.com>, Florian Weimer <fweimer@...hat.com>, kernel-hardening@...ts.openwall.com, linux-kbuild@...r.kernel.org, x86@...nel.org, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, gcc@....gnu.org, notify@...nel.org Subject: Re: [PATCH 5/5] gcc-plugins/stackleak: Don't instrument vgettimeofday.c in arm64 VDSO On Tue, Jun 09, 2020 at 12:09:27PM -0700, Kees Cook wrote: > On Thu, Jun 04, 2020 at 02:58:06PM +0100, Will Deacon wrote: > > On Thu, Jun 04, 2020 at 04:49:57PM +0300, Alexander Popov wrote: > > > Don't try instrumenting functions in arch/arm64/kernel/vdso/vgettimeofday.c. > > > Otherwise that can cause issues if the cleanup pass of stackleak gcc plugin > > > is disabled. > > > > > > Signed-off-by: Alexander Popov <alex.popov@...ux.com> > > > --- > > > arch/arm64/kernel/vdso/Makefile | 3 ++- > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile > > > index 3862cad2410c..9b84cafbd2da 100644 > > > --- a/arch/arm64/kernel/vdso/Makefile > > > +++ b/arch/arm64/kernel/vdso/Makefile > > > @@ -32,7 +32,8 @@ UBSAN_SANITIZE := n > > > OBJECT_FILES_NON_STANDARD := y > > > KCOV_INSTRUMENT := n > > > > > > -CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny -fasynchronous-unwind-tables > > > +CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny -fasynchronous-unwind-tables \ > > > + $(DISABLE_STACKLEAK_PLUGIN) > > > > I can pick this one up via arm64, thanks. Are there any other plugins we > > should be wary of? It looks like x86 filters out $(GCC_PLUGINS_CFLAGS) > > when building the vDSO. > > I didn't realize/remember that arm64 retained the kernel build flags for > vDSO builds. (I'm used to x86 throwing all its flags away for its vDSO.) > > How does 32-bit ARM do its vDSO? > > My quick run-through on plugins: > > arm_ssp_per_task_plugin.c > 32-bit ARM only (but likely needs disabling for 32-bit ARM vDSO?) On arm64, the 32-bit toolchain is picked up via CC_COMPAT -- does that still get the plugins? > cyc_complexity_plugin.c > compile-time reporting only > > latent_entropy_plugin.c > this shouldn't get triggered for the vDSO (no __latent_entropy > nor __init attributes in vDSO), but perhaps explicitly disabling > it would be a sensible thing to do, just for robustness? > > randomize_layout_plugin.c > this shouldn't get triggered (again, lacking attributes), but > should likely be disabled too. > > sancov_plugin.c > This should be tracking the KCOV directly (see > scripts/Makefile.kcov), which is already disabled here. > > structleak_plugin.c > This should be fine in the vDSO, but there's not security > boundary here, so it wouldn't be important to KEEP it enabled. Thanks for going through these. In general though, it seems like an opt-in strategy would make more sense, as it doesn't make an awful lot of sense to me for the plugins to be used to build the vDSO. So I would prefer that this patch filters out $(GCC_PLUGINS_CFLAGS). Will
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