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[84.3.50.134]) by smtp.gmail.com with ESMTPSA id x1sm10321496eji.8.2021.03.22.13.30.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Mar 2021 13:30:01 -0700 (PDT) Sender: Ingo Molnar Date: Mon, 22 Mar 2021 21:29:58 +0100 From: Ingo Molnar To: Arnd Bergmann Cc: linux-kernel@vger.kernel.org, Martin Sebor , Ning Sun , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, Arnd Bergmann , Jani Nikula , Kalle Valo , Simon Kelley , James Smart , "James E.J. Bottomley" , Anders Larsen , Tejun Heo , Serge Hallyn , Imre Deak , linux-arm-kernel@lists.infradead.org, tboot-devel@lists.sourceforge.net, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, ath11k@lists.infradead.org, linux-wireless@vger.kernel.org, netdev@vger.kernel.org, linux-scsi@vger.kernel.org, cgroups@vger.kernel.org, linux-security-module@vger.kernel.org, "H. Peter Anvin" , Andrew Morton , Lu Baolu , Will Deacon Subject: Re: [PATCH 02/11] x86: tboot: avoid Wstringop-overread-warning 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-Disposition: inline In-Reply-To: <20210322160253.4032422-3-arnd@kernel.org> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org * 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