On 5/7/25 11:38 AM, Jeremy Linton wrote:
On 5/7/25 11:31 AM, Jeremy Linton wrote:
On 5/7/25 11:12 AM, Rafael J. Wysocki wrote:
On Wed, May 7, 2025 at 5:51 PM Jeremy Linton jeremy.linton@arm.com wrote:
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 homogeneous > > Fixes: 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.
Right.
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.
Admittedly, it is not my code, but I understand this check as a termination condition for the loop: If there's not enough space in the table to hold a thing that I'm looking for, I may as well bail out.
AKA the return is still potentially returning a pointer to a structure which may not be entirely contained in the table.
Right, but this check should be made anyway before comparing cpu_node->parent to node_entry, when it is known to be a CPU entry because otherwise why bother.
Right, but then there is a clarity because really its walking the table+subtypes looking for the cpu node. Exiting early because its not big enough for a cpu node makes sense but you still need the cpu node check to avoid a variation on the original bug.
Roughly something like this:
proc_sz = sizeof(struct acpi_pptt_processor);
while ((unsigned long)entry + entry->length <= table_end) {
Here your reading the entry, without knowing its long enough. For the leaf check just using struct acpi_pptt_processor is fine, but for the acpi_find_processor_node():
proc_sz = sizeof(struct acpi_subtable_type);
Although, maybe I just wrote code that justifies using acpi_pptt_processor here because the entry->num_of_priv_resources length check isn't being made without it. So ok, use proc_sz = sizeof(struct acpi_subtable_type) and assume that we don't care if the subtable type is less than proc_sz.
Sorry for the noise, scratch that, a better solution is just to swap the length checking in the 'if' statement. Then its clear its iterating subtable types not processor nodes.
while ((unsigned long)entry + proc_sz <= table_end) { if (entry->type == ACPI_PPTT_TYPE_PROCESSOR && entry->length == sizeof(struct acpi_pptt_processor) + entry->number_of_priv_resources * sizeof(u32) && entry + entry->length <= table_end && acpi_pptt_leaf_node(...)) return (...)entry;
Although at this point the while loops entry + proc_sz could just be < table_end under the assumption that entry->length will be > 0 but whichever makes more sense.