[PATCH v2] ACPI: GTDT: Tighten the check for the array of platform timer structures

[Zheng Zengkai]

As suggested by Marc and Lorenzo, first we need to check whether the
platform_timer entry pointer is within gtdt bounds (< gtdt_end) before
de-referencing what it points at to detect the length of the platform
timer struct and then check that the length of current platform_timer
struct is within gtdt_end too. Now next_platform_timer() only checks
against gtdt_end for the entry of subsequent platform timer without
checking the length of it and will not report error if the check failed.

Add check against table length (gtdt_end) for each element of platform
timer array in acpi_gtdt_init() early, making sure that both their entry
and length actually fit in the table.

For the first platform timer, keep the check against the end of the
acpi_table_gtdt struct, it is unnecessary for subsequent platform timer.

Suggested-by: Marc Zyngier <maz@xxxxxxxxxx>
Suggested-by: Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx>
Signed-off-by: Zheng Zengkai <zhengzengkai@xxxxxxxxxx>
---
Changes in v2:
- Check against gtdt_end for both entry and len of each array element

v1: https://lore.kernel.org/all/20241010144703.113728-1-zhengzengkai@xxxxxxxxxx/
---
 drivers/acpi/arm64/gtdt.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/arm64/gtdt.c b/drivers/acpi/arm64/gtdt.c
index c0e77c1c8e09..f5f62643899d 100644
--- a/drivers/acpi/arm64/gtdt.c
+++ b/drivers/acpi/arm64/gtdt.c
@@ -157,6 +157,8 @@ int __init acpi_gtdt_init(struct acpi_table_header *table,
 {
 	void *platform_timer;
 	struct acpi_table_gtdt *gtdt;
+	struct acpi_gtdt_header *gh;
+	void *struct_end;
 
 	gtdt = container_of(table, struct acpi_table_gtdt, header);
 	acpi_gtdt_desc.gtdt = gtdt;
@@ -177,11 +179,20 @@ int __init acpi_gtdt_init(struct acpi_table_header *table,
 	}
 
 	platform_timer = (void *)gtdt + gtdt->platform_timer_offset;
-	if (platform_timer < (void *)table + sizeof(struct acpi_table_gtdt)) {
-		pr_err(FW_BUG "invalid timer data.\n");
-		return -EINVAL;
+	struct_end = (void *)table + sizeof(struct acpi_table_gtdt);
+	for (int i = 0; i < gtdt->platform_timer_count; i++) {
+		gh = platform_timer;
+		if (((i == 0 && platform_timer >= struct_end) || i != 0) &&
+			platform_timer < acpi_gtdt_desc.gtdt_end &&
+			platform_timer + gh->length <= acpi_gtdt_desc.gtdt_end) {
+			platform_timer += gh->length;
+		} else {
+			pr_err(FW_BUG "invalid timer data.\n");
+			return -EINVAL;
+		}
 	}
-	acpi_gtdt_desc.platform_timer = platform_timer;
+
+	acpi_gtdt_desc.platform_timer = (void *)gtdt + gtdt->platform_timer_offset;
 	if (platform_timer_count)
 		*platform_timer_count = gtdt->platform_timer_count;
 
-- 
2.20.1