From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 11885C30658 for ; Fri, 5 Jul 2024 07:51:46 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sPdiH-0006Wh-Jn; Fri, 05 Jul 2024 03:50:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sPdiF-0006Vs-PU; Fri, 05 Jul 2024 03:50:35 -0400 Received: from mail-pg1-x534.google.com ([2607:f8b0:4864:20::534]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1sPdiD-0001ny-Uc; Fri, 05 Jul 2024 03:50:35 -0400 Received: by mail-pg1-x534.google.com with SMTP id 41be03b00d2f7-71884eda768so826680a12.1; Fri, 05 Jul 2024 00:50:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1720165831; x=1720770631; darn=nongnu.org; h=in-reply-to:references:to:from:subject:cc:message-id:date :content-transfer-encoding:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=MY8bhF0U0Adro05b1VbDAQUEpDRF9aukSPLeIwP4jL8=; b=AYTAnJK+tHMLj1Fiaoo0Hw3l2Uz/Qqn3h8VBF362N0sTKEfOs8LhzJIefDh1e2onXd kdAYLnSBei5zSAkrxZVNXykjkiMhZfWyaI0b/iMXbtVDKUfETy1iiKx5N6bJTk1qXTm5 ex4k+Zab6Flm1RAD1TDMTlXv5ETORFGYbHB1fb4DPMpIVAVse0oIET1eVfgC8ZO2FjIt XUJO0LACcCSx9zWR4SkZJqdXSHCC15ry0uFcDtHM4sza4tU4+Ma6vTFEMcA58Ycy7RH3 0APiyFu+tYOQJr6G81J2Z2ndLsSqZUbBCZX4Jjlz3QXInUBvcfCAqtcWGK+0rr9RPGnu nbUA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1720165831; x=1720770631; h=in-reply-to:references:to:from:subject:cc:message-id:date :content-transfer-encoding:mime-version:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=MY8bhF0U0Adro05b1VbDAQUEpDRF9aukSPLeIwP4jL8=; b=ZdyXmIDZ9oCSQS1nZAc6xPXufEH/nbrzY56vjrUDnDbn5eo7cM6AWO313A6ZE5Y5He Xixo6BZ6S7RXdzrbXzXwDF0DZaY5Kxof2B1CaCZMzEFbr1aJpxFLkGEMmKkX4BkhWUsF wPQCzp8h8poNNDx4GJamvEAZDnLTSVmZGRFWVzJyvwPDi21JJgYRbUNHIReE2Q+NODV9 xsTIqXYqzlzF/bTlOvnscy/owjqofBppWA66SgtKJl28E7EZIbNVFK8q2VgCW1Cj7UB8 PiF+kb10JLNGLDmgzi9od9m79no4xie5PUdjS83CLXSo9lWKb56H5lDOrGPhIDjAV26W DCXg== X-Forwarded-Encrypted: i=1; AJvYcCVD+P25+vV8RUcAxEWqCPTQIA3lBZgpXyEstHT3GmI3sQtbOKJ8R2AZ+D7o1AsrlFlRWu5uXdsuxRMK3ydFko2KoHNlW0iOI4kNgczjVn3Lpc34mbMDUZV+jDiHBcJYJsmlsKTb/Tu3aqlEvirSJ681oQ== X-Gm-Message-State: AOJu0Yz+lLdYzYJCliTmnutx17QWH/yqjhhij8pi9fJjxvXh00k7dB3A dCWhvorwm+OscJv73P91xhi6P+hH4ykPEVwXlQsOAxWDgiGdOJnT X-Google-Smtp-Source: AGHT+IEAAeRn3j2RhQE+wS5HhoNOmptKU2aSHpunMo1xUOHvMmP0CQ/UxqDQ0FQJ9W3XSG7qv6ZAoA== X-Received: by 2002:a05:6a20:9185:b0:1be:2e11:ab28 with SMTP id adf61e73a8af0-1c0cc728cd8mr4024923637.5.1720165831288; Fri, 05 Jul 2024 00:50:31 -0700 (PDT) Received: from localhost ([1.146.70.66]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fac1535e62sm134507865ad.154.2024.07.05.00.50.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 Jul 2024 00:50:29 -0700 (PDT) Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Fri, 05 Jul 2024 17:50:17 +1000 Message-Id: Cc: "Peter Maydell" , "Akihiko Odaki" , "Eduardo Habkost" , "Marcel Apfelbaum" , =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , "Yanan Wang" , "John Snow" , "BALATON Zoltan" , "Jiaxun Yang" , "Daniel Henrique Barboza" , "Harsh Prateek Bora" , "Alexey Kardashevskiy" , "Michael S. Tsirkin" , =?utf-8?q?Alex_Benn=C3=A9e?= , "Peter Xu" , "Fabiano Rosas" , "Paolo Bonzini" , "David Hildenbrand" , "Thomas Huth" , "Laurent Vivier" , , , Subject: Re: [PATCH v2 06/15] ppc/vof: Fix unaligned FDT property access From: "Nicholas Piggin" To: "David Gibson" X-Mailer: aerc 0.17.0 References: <20240627-san-v2-0-750bb0946dbd@daynix.com> <20240627-san-v2-6-750bb0946dbd@daynix.com> In-Reply-To: Received-SPF: pass client-ip=2607:f8b0:4864:20::534; envelope-from=npiggin@gmail.com; helo=mail-pg1-x534.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri Jul 5, 2024 at 3:12 PM AEST, David Gibson wrote: > On Fri, Jul 05, 2024 at 02:40:19PM +1000, Nicholas Piggin wrote: > > On Fri Jul 5, 2024 at 11:41 AM AEST, David Gibson wrote: > > > On Fri, Jul 05, 2024 at 11:18:47AM +1000, Nicholas Piggin wrote: > > > > On Thu Jul 4, 2024 at 10:15 PM AEST, Peter Maydell wrote: > > > > > On Sat, 29 Jun 2024 at 04:17, David Gibson wrote: > > > > > > > > > > > > On Fri, Jun 28, 2024 at 04:20:02PM +0100, Peter Maydell wrote: > > > > > > > On Thu, 27 Jun 2024 at 14:39, Akihiko Odaki wrote: > > > > > > > > > > > > > > > > FDT properties are aligned by 4 bytes, not 8 bytes. > > > > > > > > > > > > > > > > Signed-off-by: Akihiko Odaki > > > > > > > > --- > > > > > > > > hw/ppc/vof.c | 2 +- > > > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > > > > > diff --git a/hw/ppc/vof.c b/hw/ppc/vof.c > > > > > > > > index e3b430a81f4f..b5b6514d79fc 100644 > > > > > > > > --- a/hw/ppc/vof.c > > > > > > > > +++ b/hw/ppc/vof.c > > > > > > > > @@ -646,7 +646,7 @@ static void vof_dt_memory_available(voi= d *fdt, GArray *claimed, uint64_t base) > > > > > > > > mem0_reg =3D fdt_getprop(fdt, offset, "reg", &proplen)= ; > > > > > > > > g_assert(mem0_reg && proplen =3D=3D sizeof(uint32_t) *= (ac + sc)); > > > > > > > > if (sc =3D=3D 2) { > > > > > > > > - mem0_end =3D be64_to_cpu(*(uint64_t *)(mem0_reg + = sizeof(uint32_t) * ac)); > > > > > > > > + mem0_end =3D ldq_be_p(mem0_reg + sizeof(uint32_t) = * ac); > > > > > > > > } else { > > > > > > > > mem0_end =3D be32_to_cpu(*(uint32_t *)(mem0_reg + = sizeof(uint32_t) * ac)); > > > > > > > > } > > > > > > > > > > > > > > I did wonder if there was a better way to do what this is doi= ng, > > > > > > > but neither we (in system/device_tree.c) nor libfdt seem to > > > > > > > provide one. > > > > > > > > > > > > libfdt does provide unaligned access helpers (fdt32_ld() etc.),= but > > > > > > not an automatic aligned-or-unaligned helper. Maybe we should= add that? > > > > > > > > > > fdt32_ld() and friends only do the "load from this bit of memory" > > > > > part, which we already have QEMU utility functions for (and which > > > > > are this patch uses). > > > > > > > > > > This particular bit of code is dealing with an fdt property ("mem= ory") > > > > > that is an array of (address, size) tuples where address and size > > > > > can independently be either 32 or 64 bits, and it wants the > > > > > size value of tuple 0. So the missing functionality is something = at > > > > > a higher level than fdt32_ld() which would let you say "give me > > > > > tuple N field X" with some way to specify the tuple layout. (Whic= h > > > > > is an awkward kind of API to write in C.) > > > > > > > > > > Slightly less general, but for this case we could perhaps have > > > > > something like the getprop equivalent of qemu_fdt_setprop_sized_c= ells(): > > > > > > > > > > uint64_t value_array[2]; > > > > > qemu_fdt_getprop_sized_cells(fdt, nodename, "memory", &value_ar= ray, > > > > > ac, sc); > > > > > /* > > > > > * fills in value_array[0] with address, value_array[1] with si= ze, > > > > > * probably barfs if the varargs-list of cell-sizes doesn't > > > > > * cover the whole property, similar to the current assert on > > > > > * proplen. > > > > > */ > > > > > mem0_end =3D value_array[0]; > > > >=20 > > > > Since 4/8 byte cells are most common and size is probably > > > > normally known, what about something simpler to start with? > > > > > > Hrm, I don't think this helps much. As Peter points out the actual > > > load isn't really the issue, it's locating the right spot for it. > >=20 > > I don't really see why that's a problem, it's just a pointer > > addition - base + fdt_address_cells * 4. The problem was in > > This is harder if #address-cells and #size-cells are different, or if > you're parsing ranges and #address-cells is different between parent > and child node. > > > the memory access (yes it's fixed with the patch but you could > > add a general libfdt way to do it). > > Huh.. well I'm getting different impressions of what the problem > actually is from what I initially read versus Peter Maydell's > comments, so I don't really know what to think. If I'm not mistaken, the sanitizer caught an unaligned 64-bit load which is the bug. The tuple address calculation itself I think is not buggy. I suppose Peter was thinking of an accessor that takes care of addressing and alignment. I don't think we're at the point it warrants it here, but could be convinced (maybe a bunch of other code would use it). I think the API is a little dangerous for overflows though, hard to static check. sscanf() style could be checked by the compiler but seems overkill to implement. > If it's just the load then fdt32_ld() etc. already exist. Or is it > really such a hot path that unconditionally handling unaligned > accesses isn't tenable? Yeah that's true, hardly any point to adding the faster variant. It could just be fixed like this then? The original patch is a fix too, but I do prefer using the same style for both, and I think using the fdt accessor is nicer to read. Thanks, Nick --- diff --git a/hw/ppc/vof.c b/hw/ppc/vof.c index e3b430a81f..a666a133d7 100644 --- a/hw/ppc/vof.c +++ b/hw/ppc/vof.c @@ -646,9 +646,9 @@ static void vof_dt_memory_available(void *fdt, GArray *= claimed, uint64_t base) mem0_reg =3D fdt_getprop(fdt, offset, "reg", &proplen); g_assert(mem0_reg && proplen =3D=3D sizeof(uint32_t) * (ac + sc)); if (sc =3D=3D 2) { - mem0_end =3D be64_to_cpu(*(uint64_t *)(mem0_reg + sizeof(uint32_t)= * ac)); + mem0_end =3D fdt64_ld((fdt64_t *)(mem0_reg + sizeof(uint32_t) * ac= )); } else { - mem0_end =3D be32_to_cpu(*(uint32_t *)(mem0_reg + sizeof(uint32_t)= * ac)); + mem0_end =3D fdt32_ld((fdt32_t *)(mem0_reg + sizeof(uint32_t) * ac= )); } g_array_sort(claimed, of_claimed_compare_func);