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Date: Wed, 14 Feb 2024 17:39:27 +0000
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Robert Richter <rrichter@....com>
CC: Alison Schofield <alison.schofield@...el.com>, Vishal Verma
<vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, Dan Williams
<dan.j.williams@...el.com>, Dave Jiang <dave.jiang@...el.com>, "Davidlohr
Bueso" <dave@...olabs.net>, "Rafael J. Wysocki" <rafael@...nel.org>, "Andrew
Morton" <akpm@...ux-foundation.org>, <linux-cxl@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, Len Brown <lenb@...nel.org>,
<linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] lib/firmware_table: Provide buffer length
argument to cdat_table_parse()
On Fri, 9 Feb 2024 20:26:47 +0100
Robert Richter <rrichter@....com> wrote:
> There exists card implementations with a CDAT table using a fix
There exist ... fixed size buffer,
> buffer, but with entries filled in that do not fill the whole table
> length size. Then, the last entry in the CDAT table may not mark the
> end of the CDAT table buffer specified by the length field in the CDAT
> header. It can be shorter with trailing unused (zero'ed) data. The
> actual table length is determined while reading all CDAT entries of
> the table with DOE.
>
> If the table is greater than expected (containing zero'ed trailing
> data), the CDAT parser fails with:
>
> [ 48.691717] Malformed DSMAS table length: (24:0)
> [ 48.702084] [CDAT:0x00] Invalid zero length
> [ 48.711460] cxl_port endpoint1: Failed to parse CDAT: -22
>
> In addition, a check of the table buffer length is missing to prevent
> an out-of-bound access then parsing the CDAT table.
>
> Hardening code against device returning borked table. Fix that by
> providing an optional buffer length argument to
> acpi_parse_entries_array() that can be used by cdat_table_parse() to
> propagate the buffer size down to its users to check the buffer
> length. This also prevents a possible out-of-bound access mentioned.
>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: Len Brown <lenb@...nel.org>
> Signed-off-by: Robert Richter <rrichter@....com>
> Reviewed-by: Dave Jiang <dave.jiang@...el.com>
I think we should scream a bit about this if we see it
as I'm unconvinced the spec allows for an implementation like this.
If the spec is unclear, lets seek a clarification.
I'm fine with this as a defensive measure, I just don't want
device vendors to keep doing it!
Jonathan
> ---
> drivers/acpi/tables.c | 2 +-
> drivers/cxl/core/cdat.c | 6 +++---
> include/linux/fw_table.h | 4 +++-
> lib/fw_table.c | 15 ++++++++++-----
> 4 files changed, 17 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
> index b07f7d091d13..b976e5fc3fbc 100644
> --- a/drivers/acpi/tables.c
> +++ b/drivers/acpi/tables.c
> @@ -253,7 +253,7 @@ int __init_or_acpilib acpi_table_parse_entries_array(
>
> count = acpi_parse_entries_array(id, table_size,
> (union fw_table_header *)table_header,
> - proc, proc_num, max_entries);
> + 0, proc, proc_num, max_entries);
>
> acpi_put_table(table_header);
> return count;
> diff --git a/drivers/cxl/core/cdat.c b/drivers/cxl/core/cdat.c
> index 6fe11546889f..012d8f2a7945 100644
> --- a/drivers/cxl/core/cdat.c
> +++ b/drivers/cxl/core/cdat.c
> @@ -149,13 +149,13 @@ static int cxl_cdat_endpoint_process(struct cxl_port *port,
> int rc;
>
> rc = cdat_table_parse(ACPI_CDAT_TYPE_DSMAS, cdat_dsmas_handler,
> - dsmas_xa, port->cdat.table);
> + dsmas_xa, port->cdat.table, port->cdat.length);
> rc = cdat_table_parse_output(rc);
> if (rc)
> return rc;
>
> rc = cdat_table_parse(ACPI_CDAT_TYPE_DSLBIS, cdat_dslbis_handler,
> - dsmas_xa, port->cdat.table);
> + dsmas_xa, port->cdat.table, port->cdat.length);
> return cdat_table_parse_output(rc);
> }
>
> @@ -511,7 +511,7 @@ void cxl_switch_parse_cdat(struct cxl_port *port)
> return;
>
> rc = cdat_table_parse(ACPI_CDAT_TYPE_SSLBIS, cdat_sslbis_handler,
> - port, port->cdat.table);
> + port, port->cdat.table, port->cdat.length);
> rc = cdat_table_parse_output(rc);
> if (rc)
> dev_dbg(&port->dev, "Failed to parse SSLBIS: %d\n", rc);
> diff --git a/include/linux/fw_table.h b/include/linux/fw_table.h
> index 95421860397a..3ff4c277296f 100644
> --- a/include/linux/fw_table.h
> +++ b/include/linux/fw_table.h
> @@ -40,12 +40,14 @@ union acpi_subtable_headers {
>
> int acpi_parse_entries_array(char *id, unsigned long table_size,
> union fw_table_header *table_header,
> + unsigned long max_length,
> struct acpi_subtable_proc *proc,
> int proc_num, unsigned int max_entries);
>
> int cdat_table_parse(enum acpi_cdat_type type,
> acpi_tbl_entry_handler_arg handler_arg, void *arg,
> - struct acpi_table_cdat *table_header);
> + struct acpi_table_cdat *table_header,
> + unsigned long length);
>
> /* CXL is the only non-ACPI consumer of the FIRMWARE_TABLE library */
> #if IS_ENABLED(CONFIG_ACPI) && !IS_ENABLED(CONFIG_CXL_BUS)
> diff --git a/lib/fw_table.c b/lib/fw_table.c
> index c3569d2ba503..16291814450e 100644
> --- a/lib/fw_table.c
> +++ b/lib/fw_table.c
> @@ -127,6 +127,7 @@ static __init_or_fwtbl_lib int call_handler(struct acpi_subtable_proc *proc,
> *
> * @id: table id (for debugging purposes)
> * @table_size: size of the root table
> + * @max_length: maximum size of the table (ignore if 0)
> * @table_header: where does the table start?
> * @proc: array of acpi_subtable_proc struct containing entry id
> * and associated handler with it
> @@ -148,18 +149,21 @@ static __init_or_fwtbl_lib int call_handler(struct acpi_subtable_proc *proc,
> int __init_or_fwtbl_lib
> acpi_parse_entries_array(char *id, unsigned long table_size,
> union fw_table_header *table_header,
> + unsigned long max_length,
> struct acpi_subtable_proc *proc,
> int proc_num, unsigned int max_entries)
> {
> - unsigned long table_end, subtable_len, entry_len;
> + unsigned long table_len, table_end, subtable_len, entry_len;
> struct acpi_subtable_entry entry;
> enum acpi_subtable_type type;
> int count = 0;
> int i;
>
> type = acpi_get_subtable_type(id);
> - table_end = (unsigned long)table_header +
> - acpi_table_get_length(type, table_header);
> + table_len = acpi_table_get_length(type, table_header);
> + if (max_length && max_length < table_len)
> + table_len = max_length;
if (max_length)
table_len = min(max_length, table_len);
> + table_end = (unsigned long)table_header + table_len;
>
> /* Parse all entries looking for a match. */
>
> @@ -208,7 +212,8 @@ int __init_or_fwtbl_lib
> cdat_table_parse(enum acpi_cdat_type type,
> acpi_tbl_entry_handler_arg handler_arg,
> void *arg,
> - struct acpi_table_cdat *table_header)
> + struct acpi_table_cdat *table_header,
> + unsigned long length)
> {
> struct acpi_subtable_proc proc = {
> .id = type,
> @@ -222,6 +227,6 @@ cdat_table_parse(enum acpi_cdat_type type,
> return acpi_parse_entries_array(ACPI_SIG_CDAT,
> sizeof(struct acpi_table_cdat),
> (union fw_table_header *)table_header,
> - &proc, 1, 0);
> + length, &proc, 1, 0);
> }
> EXPORT_SYMBOL_FWTBL_LIB(cdat_table_parse);
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