linux/drivers
Mario Limonciello f1324bbc40 tpm: disable hwrng for fTPM on some AMD designs
AMD has issued an advisory indicating that having fTPM enabled in
BIOS can cause "stuttering" in the OS.  This issue has been fixed
in newer versions of the fTPM firmware, but it's up to system
designers to decide whether to distribute it.

This issue has existed for a while, but is more prevalent starting
with kernel 6.1 because commit b006c439d5 ("hwrng: core - start
hwrng kthread also for untrusted sources") started to use the fTPM
for hwrng by default. However, all uses of /dev/hwrng result in
unacceptable stuttering.

So, simply disable registration of the defective hwrng when detecting
these faulty fTPM versions.  As this is caused by faulty firmware, it
is plausible that such a problem could also be reproduced by other TPM
interactions, but this hasn't been shown by any user's testing or reports.

It is hypothesized to be triggered more frequently by the use of the RNG
because userspace software will fetch random numbers regularly.

Intentionally continue to register other TPM functionality so that users
that rely upon PCR measurements or any storage of data will still have
access to it.  If it's found later that another TPM functionality is
exacerbating this problem a module parameter it can be turned off entirely
and a module parameter can be introduced to allow users who rely upon
fTPM functionality to turn it on even though this problem is present.

Link: https://www.amd.com/en/support/kb/faq/pa-410
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216989
Link: https://lore.kernel.org/all/20230209153120.261904-1-Jason@zx2c4.com/
Fixes: b006c439d5 ("hwrng: core - start hwrng kthread also for untrusted sources")
Cc: stable@vger.kernel.org
Cc: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Thorsten Leemhuis <regressions@leemhuis.info>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>
Tested-by: reach622@mailcuk.com
Tested-by: Bell <1138267643@qq.com>
Co-developed-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
2023-03-12 23:28:10 +02:00
..
accel
accessibility
acpi
amba
android
ata
atm
auxdisplay
base
bcma
block
bluetooth
bus
cdrom
char tpm: disable hwrng for fTPM on some AMD designs 2023-03-12 23:28:10 +02:00
clk
clocksource
comedi
connector
counter
cpufreq
cpuidle
crypto
cxl
dax
dca
devfreq
dio
dma
dma-buf
edac
eisa
extcon
firewire
firmware
fpga
fsi
gnss
gpio
gpu Merge tag 'amd-drm-fixes-6.3-2023-03-09' of https://gitlab.freedesktop.org/agd5f/linux into drm-fixes 2023-03-10 14:17:35 +10:00
greybus
hid
hsi
hte
hv
hwmon
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i2c i2c: dev: Fix bus callback return values 2023-03-09 22:07:52 +01:00
i3c
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iio
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input
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isdn
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media media: i2c: ov2685: convert to i2c's .probe_new() 2023-03-09 21:59:04 +01:00
memory
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misc misc: ad525x_dpot-i2c: Convert to i2c's .probe_new() 2023-03-09 21:58:45 +01:00
mmc
most
mtd * regression fix for the notifier handling of the I2C core 2023-03-11 09:24:05 -08:00
mux
net Networking fixes for 6.3-rc2, including fixes from netfilter, bpf 2023-03-09 10:56:58 -08:00
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scsi SCSI fixes on 20230310 2023-03-10 20:45:53 -08:00
sh
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spi
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ssb
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tc
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tty serial: sc16is7xx: Convert to i2c's .probe_new() 2023-03-09 21:58:53 +01:00
ufs
uio
usb
vdpa
vfio
vhost
video
virt
virtio
vlynq
w1 w1: ds2482: Convert to i2c's .probe_new() 2023-03-09 21:58:57 +01:00
watchdog
xen
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Kconfig
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