From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH 02/11] x86: tboot: avoid Wstringop-overread-warning Date: Mon, 22 Mar 2021 21:29:58 +0100 Message-ID: <20210322202958.GA1955909@gmail.com> References: <20210322160253.4032422-1-arnd@kernel.org> <20210322160253.4032422-3-arnd@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=7QH2qH8OXw7astC9J+hBZNIvd5jFa6HOZzbSlRf+8Ek=; b=T8MfESZQxe3NObZ/7MqvvJi28NxxdFf3ab07gERPhzLT804c2DkkhJkBMdizuiX7N5 CHF46uFWWZ0cEHLJOYnXTiyTVv5tLvjO1lmS5Ohg2XPP88nZmWW9F5ARG6cD601rZ5/K zoiBTqPm5H0nLHbAPcra7yZ3RbLdPm8oZKbWma9nQPHRlRk5CMs6B2AjWWGtpKPrvkGd rL5fFWVmWmq+K/IWUKd2YrrT8XNdUQvFpqJ+tfEUQNjkhvUoBFoAG9jEiozLdABWs7F1 P6ZC1gmMny9VZsWnwgXXF/Dsydybb92YeAKNqz04oOvYAWJ3XKyrs6O1pidMSVkxvnmE iM1A== Content-Disposition: inline In-Reply-To: <20210322160253.4032422-3-arnd@kernel.org> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" To: Arnd Bergmann Cc: dri-devel@lists.freedesktop.org, "H. Peter Anvin" , Will Deacon , linux-scsi@vger.kernel.org, x86@kernel.org, James Smart , tboot-devel@lists.sourceforge.net, Ingo Molnar , Kalle Valo , ath11k@lists.infradead.org, Serge Hallyn , Arnd Bergmann , "James E.J. Bottomley" , Ning Sun , Anders Larsen , Borislav Petkov , cgroups@vger.kernel.org, Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Martin Sebor , netdev@vger.kernel.org, linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Tejun Heo , Simon Kelley , Andrew Morton * Arnd Bergmann wrote: > From: Arnd Bergmann > > gcc-11 warns about using string operations on pointers that are > defined at compile time as offsets from a NULL pointer. Unfortunately > that also happens on the result of fix_to_virt(), which is a > compile-time constant for a constantn input: > > arch/x86/kernel/tboot.c: In function 'tboot_probe': > arch/x86/kernel/tboot.c:70:13: error: '__builtin_memcmp_eq' specified bound 16 exceeds source size 0 [-Werror=stringop-overread] > 70 | if (memcmp(&tboot_uuid, &tboot->uuid, sizeof(tboot->uuid))) { > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > I hope this can get addressed in gcc-11 before the release. > > As a workaround, split up the tboot_probe() function in two halves > to separate the pointer generation from the usage. This is a bit > ugly, and hopefully gcc understands that the code is actually correct > before it learns to peek into the noinline function. > > Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578 > Signed-off-by: Arnd Bergmann > --- > arch/x86/kernel/tboot.c | 44 ++++++++++++++++++++++++----------------- > 1 file changed, 26 insertions(+), 18 deletions(-) > > diff --git a/arch/x86/kernel/tboot.c b/arch/x86/kernel/tboot.c > index 4c09ba110204..f9af561c3cd4 100644 > --- a/arch/x86/kernel/tboot.c > +++ b/arch/x86/kernel/tboot.c > @@ -49,6 +49,30 @@ bool tboot_enabled(void) > return tboot != NULL; > } > > +/* noinline to prevent gcc from warning about dereferencing constant fixaddr */ > +static noinline __init bool check_tboot_version(void) > +{ > + if (memcmp(&tboot_uuid, &tboot->uuid, sizeof(tboot->uuid))) { > + pr_warn("tboot at 0x%llx is invalid\n", boot_params.tboot_addr); > + return false; > + } > + > + if (tboot->version < 5) { > + pr_warn("tboot version is invalid: %u\n", tboot->version); > + return false; > + } > + > + pr_info("found shared page at phys addr 0x%llx:\n", > + boot_params.tboot_addr); > + pr_debug("version: %d\n", tboot->version); > + pr_debug("log_addr: 0x%08x\n", tboot->log_addr); > + pr_debug("shutdown_entry: 0x%x\n", tboot->shutdown_entry); > + pr_debug("tboot_base: 0x%08x\n", tboot->tboot_base); > + pr_debug("tboot_size: 0x%x\n", tboot->tboot_size); > + > + return true; > +} > + > void __init tboot_probe(void) > { > /* Look for valid page-aligned address for shared page. */ > @@ -66,25 +90,9 @@ void __init tboot_probe(void) > > /* Map and check for tboot UUID. */ > set_fixmap(FIX_TBOOT_BASE, boot_params.tboot_addr); > - tboot = (struct tboot *)fix_to_virt(FIX_TBOOT_BASE); > - if (memcmp(&tboot_uuid, &tboot->uuid, sizeof(tboot->uuid))) { > - pr_warn("tboot at 0x%llx is invalid\n", boot_params.tboot_addr); > + tboot = (void *)fix_to_virt(FIX_TBOOT_BASE); > + if (!check_tboot_version()) > tboot = NULL; > - return; > - } > - if (tboot->version < 5) { > - pr_warn("tboot version is invalid: %u\n", tboot->version); > - tboot = NULL; > - return; > - } > - > - pr_info("found shared page at phys addr 0x%llx:\n", > - boot_params.tboot_addr); > - pr_debug("version: %d\n", tboot->version); > - pr_debug("log_addr: 0x%08x\n", tboot->log_addr); > - pr_debug("shutdown_entry: 0x%x\n", tboot->shutdown_entry); > - pr_debug("tboot_base: 0x%08x\n", tboot->tboot_base); > - pr_debug("tboot_size: 0x%x\n", tboot->tboot_size); This is indeed rather ugly - and the other patch that removes a debug check seems counterproductive as well. Do we know how many genuine bugs -Wstringop-overread-warning has caught or is about to catch? I.e. the real workaround might be to turn off the -Wstringop-overread-warning, until GCC-11 gets fixed? Thanks, Ingo