[PATCH] tpm/eventlog: Don't abort tpm_read_log on faulty ACPI config

[Morten Linderud <morten@linderud.pw>]

Some vendors report faulty values in the acpi TPM2 table. This causes
the function to abort with EIO and essentially short circuits the
tpm_read_log function as we never even attempt to read the EFI
configuration table for a log.

This changes the condition to only look for a positive return value,
else hands over the eventlog discovery to the EFI configuration table
which should hopefully work better.

It's unclear to me if there is a better solution to this then just
failing. However, I do not see any clear reason why we can't properly
fallback to the EFI configuration table.

The following hardware was used to test this issue on:
    Framework Laptop (Pre-production)
    BIOS: INSYDE Corp, Revision: 3.2
    TPM Device: NTC, Firmware Revision: 7.2

Dump of the fault ACPI TPM2 table:
    [000h 0000   4]                    Signature : "TPM2"    [Trusted Platform Module hardware interface Table]
    [004h 0004   4]                 Table Length : 0000004C
    [008h 0008   1]                     Revision : 04
    [009h 0009   1]                     Checksum : 2B
    [00Ah 0010   6]                       Oem ID : "INSYDE"
    [010h 0016   8]                 Oem Table ID : "TGL-ULT"
    [018h 0024   4]                 Oem Revision : 00000002
    [01Ch 0028   4]              Asl Compiler ID : "ACPI"
    [020h 0032   4]        Asl Compiler Revision : 00040000

    [024h 0036   2]               Platform Class : 0000
    [026h 0038   2]                     Reserved : 0000
    [028h 0040   8]              Control Address : 0000000000000000
    [030h 0048   4]                 Start Method : 06 [Memory Mapped I/O]

    [034h 0052  12]            Method Parameters : 00 00 00 00 00 00 00 00 00 00 00 00
    [040h 0064   4]           Minimum Log Length : 00010000
    [044h 0068   8]                  Log Address : 000000004053D000

Signed-off-by: Morten Linderud <morten@linderud.pw>
---
 drivers/char/tpm/eventlog/acpi.c   | 5 +++--
 drivers/char/tpm/eventlog/common.c | 6 +++++-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/char/tpm/eventlog/acpi.c b/drivers/char/tpm/eventlog/acpi.c
index 1b18ce5ebab1..9ce39cdb0bd8 100644
--- a/drivers/char/tpm/eventlog/acpi.c
+++ b/drivers/char/tpm/eventlog/acpi.c
@@ -136,8 +136,10 @@ int tpm_read_log_acpi(struct tpm_chip *chip)
 
 	ret = -EIO;
 	virt = acpi_os_map_iomem(start, len);
-	if (!virt)
+	if (!virt) {
+		dev_warn(&chip->dev, "%s: Failed to map acpi memory\n", __func__);
 		goto err;
+	}
 
 	memcpy_fromio(log->bios_event_log, virt, len);
 
@@ -145,7 +147,6 @@ int tpm_read_log_acpi(struct tpm_chip *chip)
 
 	if (chip->flags & TPM_CHIP_FLAG_TPM2 &&
 	    !tpm_is_tpm2_log(log->bios_event_log, len)) {
-		/* try EFI log next */
 		ret = -ENODEV;
 		goto err;
 	}
diff --git a/drivers/char/tpm/eventlog/common.c b/drivers/char/tpm/eventlog/common.c
index 8512ec76d526..f64256bc2f89 100644
--- a/drivers/char/tpm/eventlog/common.c
+++ b/drivers/char/tpm/eventlog/common.c
@@ -83,7 +83,11 @@ static int tpm_read_log(struct tpm_chip *chip)
 	}
 
 	rc = tpm_read_log_acpi(chip);
-	if (rc != -ENODEV)
+	/*
+	 * only return if we found a log else we try look for a
+	 * log in the EFI configuration table
+	 */
+	if (rc > 0)
 		return rc;
 
 	rc = tpm_read_log_efi(chip);
-- 
2.33.0