From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Mon, 7 Oct 2019 16:00:22 +0200 From: Ingo Molnar Subject: Re: [PATCH v2 5.4 regression fix] x86/boot: Provide memzero_explicit Message-ID: <20191007140022.GA29008@gmail.com> References: <20191007134724.4019-1-hdegoede@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191007134724.4019-1-hdegoede@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: To: Hans de Goede Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H . Peter Anvin" , Herbert Xu , Ard Biesheuvel , linux-crypto@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Arvind Sankar * Hans de Goede wrote: > The purgatory code now uses the shared lib/crypto/sha256.c sha256 > implementation. This needs memzero_explicit, implement this. > > Reported-by: Arvind Sankar > Fixes: 906a4bb97f5d ("crypto: sha256 - Use get/put_unaligned_be32 to get input, memzero_explicit") > Signed-off-by: Hans de Goede > --- > Changes in v2: > - Add barrier_data() call after the memset, making the function really > explicit. Using barrier_data() works fine in the purgatory (build) > environment. > --- > arch/x86/boot/compressed/string.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/arch/x86/boot/compressed/string.c b/arch/x86/boot/compressed/string.c > index 81fc1eaa3229..654a7164a702 100644 > --- a/arch/x86/boot/compressed/string.c > +++ b/arch/x86/boot/compressed/string.c > @@ -50,6 +50,12 @@ void *memset(void *s, int c, size_t n) > return s; > } > > +void memzero_explicit(void *s, size_t count) > +{ > + memset(s, 0, count); > + barrier_data(s); > +} So the barrier_data() is only there to keep LTO from optimizing out the seemingly unused function? Is there no canonical way to do that, instead of a seemingly obscure barrier_data() call - which would require a comment at minimum. We do have $(DISABLE_LTO), not sure whether it's applicable here though. Thanks, Ingo