linux-kernel - [PATCH v2 1/2] iommu/vt-d: skip RMRR entries that fail the sanity check

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Message-Id: <20200107191610.178185-2-brho@google.com>
Date:   Tue,  7 Jan 2020 14:16:09 -0500
From:   Barret Rhoden <brho@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>,
        Yian Chen <yian.chen@...el.com>,
        Sohil Mehta <sohil.mehta@...el.com>
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        x86@...nel.org
Subject: [PATCH v2 1/2] iommu/vt-d: skip RMRR entries that fail the sanity check

RMRR entries describe memory regions that are DMA targets for devices
outside the kernel's control.

RMRR entries that fail the sanity check are pointing to regions of
memory that the firmware did not tell the kernel are reserved or
otherwise should not be used.

Instead of aborting DMAR processing, this commit skips these RMRR
entries and marks the firmware as tainted.  They will not be mapped into
the IOMMU, but the IOMMU can still be utilized.  If anything, when the
IOMMU is on, those devices will not be able to clobber RAM that the
kernel has allocated from those regions.

Signed-off-by: Barret Rhoden <brho@...gle.com>
---
 drivers/iommu/intel-iommu.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 0c8d81f56a30..a8bb458845bc 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -4319,12 +4319,18 @@ int __init dmar_parse_one_rmrr(struct acpi_dmar_header *header, void *arg)
 {
 	struct acpi_dmar_reserved_memory *rmrr;
 	struct dmar_rmrr_unit *rmrru;
-	int ret;
 
 	rmrr = (struct acpi_dmar_reserved_memory *)header;
-	ret = arch_rmrr_sanity_check(rmrr);
-	if (ret)
-		return ret;
+	if (arch_rmrr_sanity_check(rmrr)) {
+		WARN_TAINT(1, TAINT_FIRMWARE_WORKAROUND,
+			   "Your BIOS is broken; bad RMRR [%#018Lx-%#018Lx]\n"
+			   "BIOS vendor: %s; Ver: %s; Product Version: %s\n",
+			   rmrr->base_address, rmrr->end_address,
+			   dmi_get_system_info(DMI_BIOS_VENDOR),
+			   dmi_get_system_info(DMI_BIOS_VERSION),
+			   dmi_get_system_info(DMI_PRODUCT_VERSION));
+		return 0;
+	}
 
 	rmrru = kzalloc(sizeof(*rmrru), GFP_KERNEL);
 	if (!rmrru)
-- 
2.24.1.735.g03f4e72817-goog