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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 <lv.zheng@intel.com>
[ rjw: Changelog, comments ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Lv Zheng 2017-06-07 12:54:58 +08:00 committed by Rafael J. Wysocki
parent 186f0a0d8e
commit 83848fbe7e
2 changed files with 39 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
drivers/acpi/acpica/tbutils.c
View File

@ -416,9 +416,18 @@ acpi_tb_get_table(struct acpi_table_desc *table_desc,
}
}
table_desc->validation_count++;
if (table_desc->validation_count == 0) {
table_desc->validation_count--;
if (table_desc->validation_count < ACPI_MAX_TABLE_VALIDATIONS) {
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) {
ACPI_WARNING((AE_INFO,
"Table %p, Validation count is zero before decrement\n",
table_desc));
return_VOID;
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 underflows\n",
table_desc));
return_VOID;
}
}
table_desc->validation_count--;
if (table_desc->validation_count == 0) {

14
include/acpi/actbl.h
View File

@ -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 */