On 5/7/25 10:42 AM, Rafael J. Wysocki wrote:
On Wed, May 7, 2025 at 5:25 PM Jeremy Linton jeremy.linton@arm.com wrote:
Hi,
On 5/6/25 8:13 AM, Heyne, Maximilian wrote:
Commit 7ab4f0e37a0f ("ACPI PPTT: Fix coding mistakes in a couple of sizeof() calls") corrects the processer entry size but unmasked a longer standing bug where the last entry in the structure can get skipped due to an off-by-one mistake if the last entry ends exactly at the end of the ACPI subtable.
The error manifests for instance on EC2 Graviton Metal instances with
ACPI PPTT: PPTT table found, but unable to locate core 63 (63) [...] ACPI: SPE must be homogeneousFixes: 2bd00bcd73e5 ("ACPI/PPTT: Add Processor Properties Topology Table parsing") Cc: stable@vger.kernel.org Signed-off-by: Maximilian Heyne mheyne@amazon.de
drivers/acpi/pptt.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c index f73ce6e13065d..4364da90902e5 100644 --- a/drivers/acpi/pptt.c +++ b/drivers/acpi/pptt.c @@ -231,7 +231,7 @@ static int acpi_pptt_leaf_node(struct acpi_table_header *table_hdr, sizeof(struct acpi_table_pptt)); proc_sz = sizeof(struct acpi_pptt_processor);
This isn't really right, it should be struct acpi_subtable_header, then once the header is safe, pull the length from it.
But then, really if we are trying to fix the original bug that the table could be shorter than the data in it suggests, the struct acpi_pptt_processor length plus its resources needs to be checked once the subtype is known to be a processor node.
Otherwise the original sizeof * change isn't really fixing anything.
Sorry, what sense did it make to do
proc_sz = sizeof(struct acpi_pptt_processor *);
here? As much as proc_sz = 0 I suppose?
No, I agree, I think the original checks were simplified along the way to that. It wasn't 'right' either.
The problem is that there are three subtypes of which processor is only one, and that struct acpi_pptt_processor doesn't necessarily reflect the actual size of the processor structure in the table because it has optional private resources tagged onto the end.
So if the bug being fixed is that the length check is validating that the table length is less than the data in the table, that's still a problem because its only validating the processor node without resources.
AKA the return is still potentially returning a pointer to a structure which may not be entirely contained in the table.
while ((unsigned long)entry + proc_sz < table_end) {
while ((unsigned long)entry + proc_sz <= table_end) { cpu_node = (struct acpi_pptt_processor *)entry; if (entry->type == ACPI_PPTT_TYPE_PROCESSOR &&And this checks if the current entry is a CPU one and goes to the next one otherwise, so it clearly looks for a CPU entry.
So the size check is logically correct now: It checks if there's enough space in the table to hold a CPU entry that's being looked for. The only problem with it is the assumption that the size of a CPU entry must be greater than sizeof(struct acpi_pptt_processor).
Previously, it didn't make sense at all.
cpu_node->parent == node_entry)@@ -273,7 +273,7 @@ static struct acpi_pptt_processor *acpi_find_processor_node(struct acpi_table_he proc_sz = sizeof(struct acpi_pptt_processor);
/* find the processor structure associated with this cpuid */
while ((unsigned long)entry + proc_sz < table_end) {
while ((unsigned long)entry + proc_sz <= table_end) { cpu_node = (struct acpi_pptt_processor *)entry; if (entry->length == 0) {