Re: [PATCH v4 0/5] Provide better MADT subtable sanity checks

From: Rafael J. Wysocki
Date: Fri Sep 25 2015 - 19:01:41 EST

On Wednesday, September 16, 2015 05:26:40 PM Al Stone wrote:
> Currently, the BAD_MADT_ENTRY macro is used to do a very simple sanity
> check on the various subtables that are defined for the MADT. The check
> compares the size of the subtable data structure as defined by ACPICA to
> the length entry in the subtable. If they are not the same, the assumption
> is that the subtable is incorrect.
> Over time, the ACPI spec has allowed for MADT subtables where this can
> never be true (the local SAPIC subtable, for example). Or, more recently,
> the spec has accumulated some minor flaws where there are three possible
> sizes for a subtable, all of which are valid, but only for specific versions
> of the spec (the GICC subtable). In both cases, BAD_MADT_ENTRY reports these
> subtables as bad when they are not. In order to retain some sanity check
> on the MADT subtables, we now have to special case these subtables. Of
> necessity, these special cases have ended up in arch-dependent code (arm64)
> or an arch has simply decided to forgo the check (ia64).
> This patch set replaces the BAD_MADT_ENTRY macro with a function called
> bad_madt_entry(). This function uses a data set of details about the
> subtables to provide more sanity checking than before:
> -- is the subtable legal for the version given in the FADT?
> -- is the subtable legal for the revision of the MADT in use?
> -- is the subtable of the proper length (including checking
> on the one variable length subtable that is currently ignored),
> given the FADT version and the MADT revision?
> Further, this patch set adds in the call to bad_madt_entry() from the
> acpi_table_parse_madt() function, allowing it to be used consistently
> by all architectures, for all subtables, and removing the need for each
> of the subtable traversal callback functions to use BAD_MADT_ENTRY.
> In theory, as the ACPI specification changes, we would only have to add
> additional information to the data set describing the MADT subtables in
> order to continue providing sanity checks, even when new subtables are
> added.
> These patches have been tested on an APM Mustang (arm64) and are known to
> work there. They have also been cross-compiled for x86 and ia64 with no
> known failures.
> Changes for v4:
> -- Remove extraneous white space change (Graeme Gregory)
> -- acpi_parse_entries() changes also needed a check to make sure that
> only MADT entries used bad_madt_entry() (Sudeep Holla)
> -- inadvertent use of 01day build noted that bad_madt_entry() can be
> static, so added it (Sudeep Holla, Fengguang Wu)
> Changes for v3:
> -- Reviewed-and-tested-by from Sudeep Holla for arm64 parts
> -- Clearer language in error messages (Graeme Gregory, Timur Tabi)
> -- Double checked that inserting call to bad_madt_entry() into the
> function acpi_parse_entries() does not impact current behavior
> (Sudeep Holla)
> Changes for v2:
> -- Acked-by on 2/5 from Marc Zyngier and Catalin Marinas for ARM
> -- Correct faulty end of loop test found by Timur Tabi
> Al Stone (5):
> ACPI: add in a bad_madt_entry() function to eventually replace the
> macro
> ACPI / IA64: remove usage of BAD_MADT_ENTRY
> ACPI / X86: remove usage of BAD_MADT_ENTRY
> ACPI: remove definition of BAD_MADT_ENTRY macro

I've queued this up for v4.4, but I had to rebase it on top of some previous
changes in my linux-next branch.

Can you please look at my bleeding-edge branch and see if the result of the
rebase is as intended? In particular, I'm not sure if we really need to return
-EINVAL from acpi_parse_entries_array() when we find a bad MADT entry or it
will be sufficient to simply go to the next entry in that case?


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