linux-kernel - Re: [PATCH v1 1/1] ACPI: NFIT: Import GUID before use

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Message-ID: <CAPcyv4jpkZNsQEvCe_dLoq0DOTrEX36vhkJg+zqEacUkJtvWiQ@mail.gmail.com>
Date:   Thu, 15 Apr 2021 22:17:09 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>
Subject: Re: [PATCH v1 1/1] ACPI: NFIT: Import GUID before use

On Thu, Apr 15, 2021 at 6:59 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> Strictly speaking the comparison between guid_t and raw buffer
> is not correct. Import GUID to variable of guid_t type and then
> compare.

Hmm, what about something like the following instead, because it adds
safety. Any concerns about evaluating x twice in a macro should be
alleviated by the fact that ARRAY_SIZE() will fail the build if (x) is
not an array.

diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index 8c5dde628405..bac01eec07a6 100644
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -681,7 +681,7 @@ int nfit_spa_type(struct acpi_nfit_system_address *spa)
        int i;

        for (i = 0; i < NFIT_UUID_MAX; i++)
-               if (guid_equal(to_nfit_uuid(i), (guid_t *)&spa->range_guid))
+               if (guid_equal(to_nfit_uuid(i), cast_guid(spa->range_guid)))
                        return i;
        return -1;
 }
diff --git a/include/linux/uuid.h b/include/linux/uuid.h
index 8cdc0d3567cd..cec1dc2ab994 100644
--- a/include/linux/uuid.h
+++ b/include/linux/uuid.h
@@ -33,6 +33,9 @@ typedef struct {
 extern const guid_t guid_null;
 extern const uuid_t uuid_null;

+#define cast_guid(x) ({ BUILD_BUG_ON(ARRAY_SIZE(x) != 16); (guid_t *)&(x); })
+#define cast_uuid(x) ({ BUILD_BUG_ON(ARRAY_SIZE(x) != 16); (uuid_t *)&(x); })
+
 static inline bool guid_equal(const guid_t *u1, const guid_t *u2)
 {
        return memcmp(u1, u2, sizeof(guid_t)) == 0;