From 83848fbe7e6af978c080a88c130a67178b1ac0e4 Mon Sep 17 00:00:00 2001 From: Lv Zheng Date: Wed, 7 Jun 2017 12:54:58 +0800 Subject: 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: Lv Zheng [ rjw: Changelog, comments ] Signed-off-by: Rafael J. Wysocki --- include/acpi/actbl.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'include') diff --git a/include/acpi/actbl.h b/include/acpi/actbl.h index d92543f3bbfd..bdc55c0da19c 100644 --- a/include/acpi/actbl.h +++ b/include/acpi/actbl.h @@ -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 */ -- cgit v1.2.3-59-g8ed1b