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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id e20sm6740048pfi.35.2019.06.22.17.00.13 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 22 Jun 2019 17:00:13 -0700 (PDT) Date: Sat, 22 Jun 2019 17:00:12 -0700 From: Kees Cook To: Matthew Garrett Cc: jmorris@namei.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Linn Crosetto , David Howells , Matthew Garrett , linux-acpi@vger.kernel.org Subject: Re: [PATCH V34 16/29] acpi: Disable ACPI table override if the kernel is locked down Message-ID: <201906221700.B1CA4EF77E@keescook> References: <20190622000358.19895-1-matthewgarrett@google.com> <20190622000358.19895-17-matthewgarrett@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190622000358.19895-17-matthewgarrett@google.com> Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Fri, Jun 21, 2019 at 05:03:45PM -0700, Matthew Garrett wrote: > From: Linn Crosetto > > From the kernel documentation (initrd_table_override.txt): > > If the ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible > to override nearly any ACPI table provided by the BIOS with an > instrumented, modified one. > > When lockdown is enabled, the kernel should disallow any unauthenticated > changes to kernel space. ACPI tables contain code invoked by the kernel, > so do not allow ACPI tables to be overridden if the kernel is locked down. > > Signed-off-by: Linn Crosetto Reviewed-by: Kees Cook -Kees > Signed-off-by: David Howells > Signed-off-by: Matthew Garrett > cc: linux-acpi@vger.kernel.org > --- > drivers/acpi/tables.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c > index 8fccbe49612a..41d9ccd0e075 100644 > --- a/drivers/acpi/tables.c > +++ b/drivers/acpi/tables.c > @@ -34,6 +34,7 @@ > #include > #include > #include > +#include > #include "internal.h" > > #ifdef CONFIG_ACPI_CUSTOM_DSDT > @@ -539,6 +540,11 @@ void __init acpi_table_upgrade(void) > if (table_nr == 0) > return; > > + if (security_locked_down(LOCKDOWN_ACPI_TABLES)) { > + pr_notice("kernel is locked down, ignoring table override\n"); > + return; > + } > + > acpi_tables_addr = > memblock_find_in_range(0, ACPI_TABLE_UPGRADE_MAX_PHYS, > all_tables_size, PAGE_SIZE); > -- > 2.22.0.410.gd8fdbe21b5-goog > -- Kees Cook