Commit 83848fbe authored by Lv Zheng's avatar Lv Zheng Committed by Rafael J. Wysocki
Browse files

ACPICA: Tables: Mechanism to handle late stage acpi_get_table() imbalance 



Considering this case:

 1. A program opens a sysfs table file 65535 times, it can increase
    validation_count and first increment cause the table to be mapped:

     validation_count = 65535

 2. AML execution causes "Load" to be executed on the same
    table, this time it cannot increase validation_count, so
    validation_count remains:

      validation_count = 65535

 3. The program closes sysfs table file 65535 times, it can decrease
    validation_count and the last decrement cause the table to be
    unmapped:

     validation_count = 0

 4. AML code still accessing the loaded table, kernel crash can be
    observed.

To prevent that from happening, add a validation_count threashold.
When it is reached, the validation_count can no longer be
incremented/decremented to invalidate the table descriptor (means
preventing table unmappings)

Note that code added in acpi_tb_put_table() is actually a no-op but
changes the warning message into a "warn once" one. Lv Zheng.

Signed-off-by: default avatarLv Zheng <lv.zheng@intel.com>
[ rjw: Changelog, comments ]
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 186f0a0d

drivers/acpi/acpica/tbutils.c

+25 −9
Original line number Diff line number Diff line
@@ -416,9 +416,18 @@ acpi_tb_get_table(struct acpi_table_desc *table_desc, 
		}

	}



	if (table_desc->validation_count < ACPI_MAX_TABLE_VALIDATIONS) {

		table_desc->validation_count++;

	if (table_desc->validation_count == 0) {

		table_desc->validation_count--;



		/*

		 * Detect validation_count overflows to ensure that the warning

		 * message will only be printed once.

		 */

		if (table_desc->validation_count >= ACPI_MAX_TABLE_VALIDATIONS) {

			ACPI_WARNING((AE_INFO,

				      "Table %p, Validation count overflows\n",

				      table_desc));

		}

	}



	*out_table = table_desc->pointer;
@@ -445,13 +454,20 @@ void acpi_tb_put_table(struct acpi_table_desc *table_desc) 


	ACPI_FUNCTION_TRACE(acpi_tb_put_table);



	if (table_desc->validation_count == 0) {

	if (table_desc->validation_count < ACPI_MAX_TABLE_VALIDATIONS) {

		table_desc->validation_count--;



		/*

		 * Detect validation_count underflows to ensure that the warning

		 * message will only be printed once.

		 */

		if (table_desc->validation_count >= ACPI_MAX_TABLE_VALIDATIONS) {

			ACPI_WARNING((AE_INFO,

			      "Table %p, Validation count is zero before decrement\n",

				      "Table %p, Validation count underflows\n",

				      table_desc));

			return_VOID;

		}

	table_desc->validation_count--;

	}



	if (table_desc->validation_count == 0) {

include/acpi/actbl.h

+14 −0
Original line number Diff line number Diff line
@@ -374,6 +374,20 @@ struct acpi_table_desc { 
	u16 validation_count;

};



/*

 * Maximum value of the validation_count field in struct acpi_table_desc.

 * When reached, validation_count cannot be changed any more and the table will

 * be permanently regarded as validated.

 *

 * This is to prevent situations in which unbalanced table get/put operations

 * may cause premature table unmapping in the OS to happen.

 *

 * The maximum validation count can be defined to any value, but should be

 * greater than the maximum number of OS early stage mapping slots to avoid

 * leaking early stage table mappings to the late stage.

 */

#define ACPI_MAX_TABLE_VALIDATIONS          ACPI_UINT16_MAX



/* Masks for Flags field above */



#define ACPI_TABLE_ORIGIN_EXTERNAL_VIRTUAL  (0)	/* Virtual address, external maintained */

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