[PATCH v4] 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 also valid, i.e. the length is not zero and within gtdt_end.
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 and the existing check in function
acpi_gtdt_init() is also not enough.

Modify the for_each_platform_timer() iterator and use it combined with
a dedicated check function platform_timer_valid() to do the check
against table length (gtdt_end) for each element of platform timer
array in function acpi_gtdt_init(), making sure that both their entry
and length actually fit in the table.

Suggested-by: Lorenzo Pieralisi <lpieralisi at kernel.org>
Co-developed-by: Marc Zyngier <maz at kernel.org>
Signed-off-by: Marc Zyngier <maz at kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai at huawei.com>
---
Changes in v4:
- remove the tmp pointer to make the code more concise.

Changes in v3:
- based on Marc's patch and reuse the for_each_platform_timer() loop
Link to v3: https://lore.kernel.org/linux-arm-kernel/20241015152602.184108-1-zhengzengkai@huawei.com/

Changes in v2:
- Check against gtdt_end for both entry and len of each array element
Link to v2: https://lore.kernel.org/linux-arm-kernel/20241012085343.6594-1-zhengzengkai@huawei.com/

Link to v1: https://lore.kernel.org/all/20241010144703.113728-1-zhengzengkai@huawei.com/

Link to previous related patches:
https://lore.kernel.org/all/20241008082429.33646-1-zhengzengkai@huawei.com/
https://lore.kernel.org/all/20240930030716.179992-1-zhengzengkai@huawei.com/
---
 drivers/acpi/arm64/gtdt.c | 29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/drivers/acpi/arm64/gtdt.c b/drivers/acpi/arm64/gtdt.c
index c0e77c1c8e09..d7c4e1b9915b 100644
--- a/drivers/acpi/arm64/gtdt.c
+++ b/drivers/acpi/arm64/gtdt.c
@@ -36,19 +36,25 @@ struct acpi_gtdt_descriptor {
 
 static struct acpi_gtdt_descriptor acpi_gtdt_desc __initdata;
 
-static inline __init void *next_platform_timer(void *platform_timer)
+static __init bool platform_timer_valid(void *platform_timer)
 {
 	struct acpi_gtdt_header *gh = platform_timer;
 
-	platform_timer += gh->length;
-	if (platform_timer < acpi_gtdt_desc.gtdt_end)
-		return platform_timer;
+	return (platform_timer >= (void *)(acpi_gtdt_desc.gtdt + 1) &&
+		platform_timer < acpi_gtdt_desc.gtdt_end &&
+		gh->length != 0 &&
+		platform_timer + gh->length <= acpi_gtdt_desc.gtdt_end);
+}
+
+static __init void *next_platform_timer(void *platform_timer)
+{
+	struct acpi_gtdt_header *gh = platform_timer;
 
-	return NULL;
+	return platform_timer + gh->length;
 }
 
 #define for_each_platform_timer(_g)				\
-	for (_g = acpi_gtdt_desc.platform_timer; _g;	\
+	for (_g = acpi_gtdt_desc.platform_timer; platform_timer_valid(_g);\
 	     _g = next_platform_timer(_g))
 
 static inline bool is_timer_block(void *platform_timer)
@@ -157,6 +163,7 @@ int __init acpi_gtdt_init(struct acpi_table_header *table,
 {
 	void *platform_timer;
 	struct acpi_table_gtdt *gtdt;
+	int cnt = 0;
 
 	gtdt = container_of(table, struct acpi_table_gtdt, header);
 	acpi_gtdt_desc.gtdt = gtdt;
@@ -176,12 +183,16 @@ int __init acpi_gtdt_init(struct acpi_table_header *table,
 		return 0;
 	}
 
-	platform_timer = (void *)gtdt + gtdt->platform_timer_offset;
-	if (platform_timer < (void *)table + sizeof(struct acpi_table_gtdt)) {
+	acpi_gtdt_desc.platform_timer = (void *)gtdt + gtdt->platform_timer_offset;
+	for_each_platform_timer(platform_timer)
+		cnt++;
+
+	if (cnt != gtdt->platform_timer_count) {
+		acpi_gtdt_desc.platform_timer = NULL;
 		pr_err(FW_BUG "invalid timer data.\n");
 		return -EINVAL;
 	}
-	acpi_gtdt_desc.platform_timer = platform_timer;
+
 	if (platform_timer_count)
 		*platform_timer_count = gtdt->platform_timer_count;
 
-- 
2.20.1