Hi Lorenzo,
On Tue, Jan 28, 2025 at 11:50:55AM +0100, Lorenzo Pieralisi wrote:
@@ -188,13 +188,17 @@ int __init acpi_gtdt_init(struct acpi_table_header *table, cnt++; if (cnt != gtdt->platform_timer_count) {
cnt = min(cnt, gtdt->platform_timer_count);Thank you for reporting this.
There is something I need to understand.
What's wrong cnt (because platform_timer_valid() fails for some reason on some entries whereas before the commit we are fixing was applied we *were* parsing those entries) or gtdt->platform_timer_count ?
I *guess* the issue is the following:
gtdt->platform_timer_count reports the number of GT blocks in the GTDT not including Arm generic watchdogs, whereas cnt counts both structure types (and that's what gtdt->platform_timer_count should report too if it was correct).
I've seen two different issues so far:
- In one case, the offset of the platform timer array is entirely beyond the GTDT
- In another, the GTDT has a timer array of length 2, but only the first structure falls within the length of the overall GTDT
Since cnt is the result of doing a bounds-checked walk of the platform timer array, both of these issues cause the sanity check to fail.
if (platform_timer_count)
*platform_timer_count = gtdt->platform_timer_count;
*platform_timer_count = cnt;I think this should be fine as things stand (but see above).
It is used in:
gtdt_sbsa_gwdt_init() - just to check if there are platform timers entries
arch_timer_mem_acpi_init() - to create a temporary array to init arch mem timer entries (the array is oversized because it includes watchdog entries in the count)
In both cases taking the
min(cnt, gtdt->platform_timer_count);
should work AFAICS
It was probably worth noting in the changelog that I did this to gracefully handle the reverse of this issue where we could dereference platform timer entries that are within the bounds of the GTDT but exceed gtdt->platform_timer_count.
(hard to grok though, we - as in ACPI maintainers - need to clean this up).
Heh, thought this smelled a little ripe ;-) Went for the minimal fix first.