From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail05.groups.io (mail05.groups.io [45.79.224.7]) by spool.mail.gandi.net (Postfix) with ESMTPS id F3D2274003A for ; Wed, 15 Jan 2025 18:53:02 +0000 (UTC) DKIM-Signature: a=rsa-sha256; bh=mY0s7FDYzHAosT1ijI1ZOFWAjwiqphQyIoM/c9Q3Jwc=; c=relaxed/simple; d=groups.io; h=Message-ID:Date:MIME-Version:User-Agent:Subject:To:Cc:References:From:In-Reply-To:Precedence:List-Subscribe:List-Help:Sender:List-Id:Mailing-List:Delivered-To:Resent-Date:Resent-From:Reply-To:List-Unsubscribe-Post:List-Unsubscribe:Content-Language:Content-Type:Content-Transfer-Encoding; s=20240830; t=1736967182; v=1; x=1737226381; b=gLScR7PVu73Uvipd8dLi7CemXJ004Iv+EhHPMIPWYfYBXJT98OD5FB7gHdmXlkacrm+NlAEn wruMC9SvfmhunxS311uGOCwPR+ePBUNpEYgrAQiTBdRMSF4weLTDXLepmxzza/QWHlR50KxV/Th DDzoes0caD+p+TMf/0PI4j/8hjqnrfa5WPsKyjjEHbWU/mAAg3gH15TK88bJDAm+/T5vE64D+fM KeEP23zeTZrzSYbQsa+GAOLQb21ik/JsambqXcubjz8zPZ1oAE/qWeFSrk8VlFqI1UsleU888fP rT2NmSguUYhmK9fDJwAYsiQvK5eHupAnRo34kqQHWm0DA== X-Received: by 127.0.0.2 with SMTP id WIV3YY7687511xPYSS927Khz; Wed, 15 Jan 2025 10:53:01 -0800 X-Received: from mail-ed1-f42.google.com (mail-ed1-f42.google.com [209.85.208.42]) by mx.groups.io with SMTP id smtpd.web11.1127.1736440580829863505 for ; Thu, 09 Jan 2025 08:36:21 -0800 X-Received: by mail-ed1-f42.google.com with SMTP id 4fb4d7f45d1cf-5d90a5581fcso1747011a12.1 for ; Thu, 09 Jan 2025 08:36:20 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCXCkxBXijlmxWwuo4v3eNXNmXmVhdTd/SlSeYsiVv5YuXka/B/eJk2yibnv2Vg7StMqVUswUA==@edk2.groups.io X-Gm-Message-State: Kyik5vvSVTertVgtoJPzFv0wx7686176AA= X-Gm-Gg: ASbGncsKWPfeBkt2Qsg8USSW5yia/U27nEczACzdRNowtAOLp4hQT3bg34ROfWNZnA1 I8+5oT4ygLopnJ56J4S0/RnCNJ5PjRVGLegXCEvimDk8PFrEI099otIbgbkIIHgxdFgTo3qh1pq sKTiNEQ6PPHfFHuPY9FIHcS5SjqtONhEoHVB4EBtn3HVWJCbaxyJ3KgXNJXhveESEN7dfKy5Pdk xXbN/T/3BhVAl8j4a+J0RFbC9MHqlfZCNuaF+9tGVOpjxKbWupNCu5wKx6My5CoC8NhlCtc+emH YK3BiqDZ35E4hGD/ci0/tGrrzOij X-Google-Smtp-Source: AGHT+IFH4Mf4jMgpRx3khbxhhYmeEL2WA8ovuW6XBYno3NsJIZaj1ShKSo8fqHjrVfklGFxDEAk+6g== X-Received: by 2002:a05:6402:1ed4:b0:5d0:bcdd:ff8f with SMTP id 4fb4d7f45d1cf-5d972dfbcc3mr6581488a12.4.1736440578846; Thu, 09 Jan 2025 08:36:18 -0800 (PST) X-Received: from ?IPV6:2a03:83e0:1126:4:829:739b:3caa:6500? ([2620:10d:c092:500::5:337c]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5d9903c3333sm785494a12.47.2025.01.09.08.36.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Jan 2025 08:36:18 -0800 (PST) Message-ID: Date: Thu, 9 Jan 2025 16:36:17 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [edk2-devel] [RFC 1/2] efi/memattr: Use desc_size instead of total size to check for corruption To: Ard Biesheuvel Cc: linux-efi@vger.kernel.org, devel@edk2.groups.io, kexec@lists.infradead.org, hannes@cmpxchg.org, dyoung@redhat.com, x86@kernel.org, linux-kernel@vger.kernel.org, leitao@debian.org, gourry@gourry.net, kernel-team@meta.com References: <20250108215957.3437660-1-usamaarif642@gmail.com> <20250108215957.3437660-2-usamaarif642@gmail.com> From: "Usama Arif via groups.io" In-Reply-To: Precedence: Bulk List-Subscribe: List-Help: Sender: devel@edk2.groups.io List-Id: Mailing-List: list devel@edk2.groups.io; contact devel+owner@edk2.groups.io Resent-Date: Wed, 15 Jan 2025 10:52:52 -0800 Resent-From: usamaarif642@gmail.com Reply-To: devel@edk2.groups.io,usamaarif642@gmail.com List-Unsubscribe-Post: List-Unsubscribe=One-Click List-Unsubscribe: Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-GND-Status: LEGIT Authentication-Results: spool.mail.gandi.net; dkim=pass header.d=groups.io header.s=20240830 header.b=gLScR7PV; dmarc=pass (policy=none) header.from=groups.io; spf=pass (spool.mail.gandi.net: domain of bounce@groups.io designates 45.79.224.7 as permitted sender) smtp.mailfrom=bounce@groups.io On 09/01/2025 15:45, Ard Biesheuvel wrote: > On Wed, 8 Jan 2025 at 23:00, Usama Arif wrote: >> >> The commit in [1] introduced a check to see if EFI memory attributes >> table was corrupted. It assumed that efi.memmap.nr_map remains >> constant, but it changes during late boot. >> Hence, the check is valid during cold boot, but not in the subsequent >> kexec boot. >> >> This is best explained with an exampled. At cold boot, for a test >> machine: >> efi.memmap.nr_map=3D91, >> memory_attributes_table->num_entries=3D48, >> desc_size =3D 48 >> Hence, the check introduced in [1] where 3x the size of the >> entire EFI memory map is a reasonable upper bound for the size of this >> table is valid. >> >> In late boot __efi_enter_virtual_mode calls 2 functions that updates >> efi.memmap.nr_map: >> - efi_map_regions which reduces the `count` of map entries >> (for e.g. if should_map_region returns false) and which is reflected >> in efi.memmap by __efi_memmap_init. >> At this point efi.memmap.nr_map becomes 46 in the test machine. >> - efi_free_boot_services which also reduces the number of memory regions >> available (for e.g. if md->type or md->attribute is not the right valu= e). >> At this point efi.memmap.nr_map becomes 9 in the test machine. >> Hence when you kexec into a new kernel and pass efi.memmap, the >> paramaters that are compared are: >> efi.memmap.nr_map=3D9, >> memory_attributes_table->num_entries=3D48, >> desc_size =3D 48 >> where the check in [1] is no longer valid with such a low efi.memmap.nr_= map >> as it was reduced due to efi_map_regions and efi_free_boot_services. >> >> A more appropriate check is to see if the description size reported by >> efi and memory attributes table is the same. >> >> [1] https://lore.kernel.org/all/20241031175822.2952471-2-ardb+git@google= .com/ >> >> Fixes: 8fbe4c49c0cc ("efi/memattr: Ignore table if the size is clearly b= ogus") >> Reported-by: Breno Leitao >> Signed-off-by: Usama Arif >> --- >> drivers/firmware/efi/memattr.c | 16 ++++++---------- >> 1 file changed, 6 insertions(+), 10 deletions(-) >> >=20 > The more I think about this, the more I feel that kexec on x86 should > simply discard this table, and run with the firmware code RWX (which > is not the end of the world). By discard this table, do you mean kexec not use e820_table_firmware? Also a very basic question, what do you mean by run with the firmware RWX? Sorry for the very basic questions above! >=20 > The main reason is that the EFI memory map and the EFI memory > attributes table are supposed to be a matched pair, where each RTcode > entry in the former is broken down into multiple code and data > segments in the latter. The amount of mangling that the x86 arch code > does of the EFI memory map makes it intractable to ensure that they > remain in sync, and so it is better not to bother. >=20 >=20 >> diff --git a/drivers/firmware/efi/memattr.c b/drivers/firmware/efi/memat= tr.c >> index c38b1a335590..d3bc161361fb 100644 >> --- a/drivers/firmware/efi/memattr.c >> +++ b/drivers/firmware/efi/memattr.c >> @@ -40,21 +40,17 @@ int __init efi_memattr_init(void) >> goto unmap; >> } >> >> - >> /* >> - * Sanity check: the Memory Attributes Table contains up to 3 en= tries >> - * for each entry of type EfiRuntimeServicesCode in the EFI memo= ry map. >> - * So if the size of the table exceeds 3x the size of the entire= EFI >> - * memory map, there is clearly something wrong, and the table s= hould >> - * just be ignored altogether. >> + * Sanity check: the Memory Attributes Table desc_size and >> + * efi.memmap.desc_size should match. >> */ >> - size =3D tbl->num_entries * tbl->desc_size; >> - if (size > 3 * efi.memmap.nr_map * efi.memmap.desc_size) { >> - pr_warn(FW_BUG "Corrupted EFI Memory Attributes Table de= tected! (version =3D=3D %u, desc_size =3D=3D %u, num_entries =3D=3D %u)\n", >> - tbl->version, tbl->desc_size, tbl->num_entries); >> + if (efi.memmap.desc_size !=3D tbl->desc_size) { >> + pr_warn(FW_BUG "Corrupted EFI Memory Attributes Table de= tected! (version =3D=3D %u, table desc_size =3D=3D %u, efi.memmap.desc_size= =3D=3D %lu, table num_entries =3D=3D %u)\n", >> + tbl->version, tbl->desc_size, efi.memmap.desc_si= ze, tbl->num_entries); >> goto unmap; >> } >> >> + size =3D tbl->num_entries * tbl->desc_size; >> tbl_size =3D sizeof(*tbl) + size; >> memblock_reserve(efi_mem_attr_table, tbl_size); >> set_bit(EFI_MEM_ATTR, &efi.flags); >> -- >> 2.43.5 >> -=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#121005): https://edk2.groups.io/g/devel/message/121005 Mute This Topic: https://groups.io/mt/110517813/7686176 Group Owner: devel+owner@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io] -=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-