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    SubjectRe: [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@amd.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@kernel.org>
    > Cc: Len Brown <lenb@kernel.org>
    > Signed-off-by: Robert Richter <rrichter@amd.com>
    > Reviewed-by: Dave Jiang <dave.jiang@intel.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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